Medical Entrance 2012

Animal Tissues

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:58:00 +0000

Body of a multicellular animal is formed of many cells. Group of cells similar in structure , function and origin form a "Tissue". Branch of Biology that deals with the study of tissues is known as 'Histology'.
Animal cells have narrow space around them which contains fluid called as Extra cellular fluid/ Intercellular fluid.

ORIGIN OF TISSUES: All tissues originate from the cells of any of the three germ layers - ectoderm, mesoderm and endoderm.

TYPES OF TISSUES: 4 major types of tissues are there- Epithelial tissues, Connective tissues, Muscular Tissue and Nervous Tissue.

1.1. Epithelial Tissues : ( Gr. Epi - Upon thele - nipple)
Epithelial tissues are the tissues composed of one or more layers of cells covering the external surface of the body and internal organs or lining the cavities in the body and viscera
There are no blood vessels supplying nourishment to these tissues but they receive nutrients from underlying connective tissues.

Structure: These tissues consist of variously shaped cells arranged closely in one /more layers. There is little intercellular material between the cells and cells are held together by intercellular junctions. Epithelia rests on a thin basement membrane which is made up of Glycoproteins and collagen fibres.

Types: On the basis of arrangement and shape of cells, the epithelia are classified into two groups:-
Covering & Glandular Epithelia

A. COVERING EPITHELIA: These cover the external surface or lining or the cavities. It is of 2 types - Simple & Compound.

(i) Simple Epithelia: They consist of single layer of cells resting on basement membrane. These cover the surface where there is lesser wear & tear. These are further of five types: -

(a) Simple Squamous Epithelium : Consist of thin flat, polygonal closely fitted cells like the floor tiles. So it is also known as ' pavement epithelium'. It has round/oval nucleus. Present on inner lining of lung alveoli, blood vesse;s and peritoneum of bodyearity. Function: protection , excretion, gaseous exchange

(b) Simple Cuboidal Epithelium : Consists of polygonal cells which appear cuboidal . These are found in proximal tubules of kidneys, salivary glands, pancreatic ducts, thyroid follicles & ovary. Function: Protection, secretion of juices, excretion, absorption.

(c) Simple Columnar Epithelium: In this, cells are tall and placed side by side like column. Nucleus is oval . Found in inner surface of intestine, gall bladders, stomach, gastric & intestinal glands. Function : Secretion , absorption

(d) Simple Ciliated Epithelium: These consist of cells that bear fine , cytoplasmic process 'cilia' on the free surface. It lines the inner surface of some hollow organs like fallopian tubes, nasal passage, bronchioles etc. Function: Cilia help in movement of particles, free cells or mucus over the epithelial surface

(e) Pseudo-Stratified Epithelium : consist of ciliated or non-ciliated epithelium in which columnar cells are arranged in single layer but appear multilayered because some cells are shorter than others. It covers the inner lining of trachea, large bronchi. Functions: Protection, movement of secretion from glands

(ii) Compound Epithelium : It consists of many layer of cells which may be different in shape. Deepest layer rests on basement membrane. Layers of cells give a stratified appearance . So, it is also known as 'Stratified Epithelium'. Based upon the shape of cells in outer layer, compound epithelium is mainly of four types:-

(a) Stratified Squamous: Cells have different shapes in different layers. Deepest layer have columnar or cuboidal cells with oval nuclei. These divide by mitosis & add new cells to outer layers. It is called 'Germinative layer'. Middle layer cells are polyhedral with round nuclei. It is called ' Intermediate layer' Superficial layers are flat with elongated nuclei. These layers are called Squamous layers. It is of two types - keratinized & non- keratinized.
Keratinized squamous epithelium has Keratin in place of cytoplasm in few outer layers. It forms epidermis of skin in land vertebrates. Cells in outer layers ( with keratin) are dead. Non-keratinized squamous epithelium does not have keratin. So cells on outer layer are living . It covers moist surfaces like buccal cavity, pharynx, oesophagus, cornea of eye. It provides moderate protection against abrasion.

(b) Stratified Cuboidal Epithelium : Outer layer has cuboidal cells .Basal layer has columnar cells. It forms epidermis of fish , lines the sweat gland ducts, salivary ducts and pancreatic ducts.

(c) Stratified Columnar Epithelium : It has columnar cells in outermost & innermost layers. It covers epiglottis , lines the mammary gland ducts and parts of urethra.

(d) Stratified Ciliated Columnar Epithelium : Outer layer has ciliated columnar cells. Basal layer has columnar cells. It lines the larynx & upper part of soft palate.

Other types of compound epithelia is
Transitional Epithelium : Superficial layer has blood, rectangular/oval cells. Middle layer has polygonal or pear shaped cells. Basal layer has cuboidal cells. Cells can change from simple to compound epithelium i.e. they are in transitional phase. It lines inner surface of ureter, urinary bladder etc. and can stretch . It prevents loss of water & helps in expansion of organs by stretching.
Other types of epithelia which are neither simple nor compound type are

Neuroepithelial cells: These perform sensory function, e.g. cells of taste bud
Myoepithelial cells: Branched cells and contain muscle protein ( myosin & actin) . These play role in contraction of muscles.

B. GLANDULAR EPITHELIA : It has columnar cells which secrete useful materials like secretions of glands. The epithelia forms glands also. Glands can be of following types:-

(i) Unicellular: These consist of isolated glandular cells. e.g. goblet cells & alimentary canal.

(ii) Multicellular: - These glands consists of a cluster of cells.

(iii) Simple Gland: -A gland with single unbranched duct is called Simple gland. e.g. Tubular gland in human intestine. The secretory part of the gland consists of epithelial cells arranged as tubes (tubular) or sacs (acini, alveoli) or both.

(v) Compound Gland: - A gland with branched system of ducts is called as compound gland. e.g. Gland in Pancreas and sub-mandibular salivary glands. In these tubules/acinus of secretory duct may be coiled or branched and opens in to single duct.

(v) Exocrine Glands: -These glands transport their seceretions to the site of action by ducts. e.g. Salivary gland, tear gland, Gastric gland, Intestinal gland.

(vi) Endocrine Glands: - (Ductless glands): These discharge their seceretions called 'hormones' into blood which carries them to the site of action. e.g. Pituitary gland, Thyroid gland, Adrenal gland.

(vii) Mixed Gland: -When a gland performs both, exocrine and endocrine functions, it is called Mixed Gland. e.g. Pancreas.

(viii) Holocrine Glands: -In these, whole cell fills with seceretion and later breaks down and is shed as secretion. e.g. Sebaceous Glands.

(ix) Merocrine Glands: -The secretion leaves the cell through cell membrane and cell contents remain intact. e.g. Pancreas.

(x) Apocrine Glands: -In these, only apical portion of the cytoplasm is discharged along with secretory product. e.g. Mammary Glands.

1.2 CONNECTIVE TISSUE: - It is made up of variously shaped, loosely arranged cells lying in the extra cellular matrix.
Extra cellular matrix has protein fibres, tissue fluid and amorphous ground substance (glycoaminoglycans+glycoproteins).
Connective tissue play a role in defence, tissue repair, fat storage etc.

Types: - 8 types of connective tissues are there:-

(i) Areolar Tissue : - (Loose connective Tissue). It is found beneath epithelia of many viscenal organs. It joins different tissues and forms packing between them. Three types of cells are present in this tissue: -

(a) Fibroblast: -are main cells, have irregular flat cells with protoplasmic processes. These synthesize proteins collagen and elastin.

(b) Macrophages: -These destroy microbes, foreign particles and cells of damaged tissues by phagocytosis.

(c) Mast Cells: -large, irregular, ovoid cells. These store inflammation producing substances which are released at the place of injury.

Two types of fibres are present in this tissue: -

(a) White collagen fibre: - made of collagen protein, occur as bundles, lack elasticity.

(b) Yellow elastic fibre: -made of elastin protein, don't occur as bundles, are elastic in nature. Both fibres prevent displacement and injury of tissues and organs. Collagen fibres are formed at the site of injury.

(ii) Adipose Tissue: -It is a fat-storing connective tissue-found beneath skin, around kidneys & other places. It contains fat cells 'adipocytes' , fibroblasts, macrophages, collagen fibres & elastic fibres. Function: -synthesizes and stores fat, acts as shock absorber and prevents heat loss by forming insulating layer.

(iii) White tissue: - It has few fibroblasts scattered in the dense network of thick collagen fibre bundles. Function: -As it has great strength, it provides strong attachment between various structures.

(iv) Tendon: -It is formed of bundles of collagen fibres arranged parallely. Fibroblast cells occur in these. Function: -These connect skeletal muscles with bone.

(v) Ligament: - It is made of yellow elastin fibres which forms densely crowded matrix. Fibroblasts lie scattered in these. Function: -It connects the bones at joints and provides movability.

(vi) Cartilage: -It is solid, semi-rigid connective tissue. It contains matrix made of Chondrin (consists proteoglycans). Cartilage cells 'Chondriocytes' lie scattered in the matrix in small spaces called 'lacunae' in the clusters of two or three: -

Four types of cartilages are there: -

(a) Hyaline: -blue in colour, matrix is clear, translucent & lacks fibres. Present in sternum, hyoid & ribs.

(b) Fibrous: -contains matrix rich in bundles of collagen fibres & chondrocytes. Found in intervertebral disc.

(c) Elastic: -It consists of yellow elastin fibres and is elastic in nature. Seen in pinna, tip of nose, epiglottis.

(d) Calcified: -initially like hyaline cartilage. Later it gets hardened due to deposition of calcium salts. e.g. pubis of pectoral gindle of frog.

(vii) Bone: -It is solid, rigid and hardest connective tissue. It has matrix (made of protein 'Ossein', sulphates, carbonates and fluoride salts of Ca & Mg), irregular spaces 'lacunae' in the matrix and osteocytes (bone cells) in the lacunae.
Compact bone forms dense outer layer of all the bones and is made of parallely & longitudinally arranged column like structures-Haversian system. Each Haversian system has a central canal (Haversian canal) and many lamellae surround it. This canal has blood vessels & nerves. Hollow cavities are called 'Marrow cavities' and are filled with bone marrow.

Types: -2 types -Compact & Spongy.
Shaft of long bones are compact bones. These have lamellae around canal without gaps.
Spongy bones have trabeculae, forming network with small spaces between them. Spaces have red bone marrow, which forms WBC & RBC.

(viii) Blood: -It is fluid connective tissue composed of plasma and blood corpuscles. Blood is also called 'Vascular tissue' because it is part of the vascular system of many animals.

Plasma-is yellow, slightly alkaline (pH 7.4) , somewhat viscous fluid. It has 92% water & 8% solid. There are three plasma proteins-albumin, globulin, fibrinogen. Solutes present in plasma are glucose protein, amino acids, cholesterol, fatty acids, vitamins, enzymes, hormones, antibodies etc. Inorganic salts present in plasma are ions of Na, Mg, K, Ca, etc. Normal blood-sugar level is 90-120 mg/100 ml blood. Blood Corpuscles are of three types-RBC, WBC and Platelets.

RBCs (Erythrocytes) are red in colour due to red pigment haemoglobin. It may be nucleated/non-nucleated. Shape varies, size ranges from 7-8 m in diameter. Adult woman has 4-5 million RBCs/cu mm of blood. Adult man has 5.5 million/cu mm of blood.

Haemoglobin (Hb) is a protein made of protein globin and ferrous (Fe²⁺) containing tetrapyrole porphyrin ring called 'Haeme'. 1 molecule of HB binds to four molecules of oxygen.

RBCs have an average life span of about 120 days. WBCs (leucocytes) are colourless & nucleated. Their number in adult human is 7.5 3.5 × 10³ per cubic mm of blood. These are of two types - Granulocytes (with granules in cytoplasm) and Agranulocytes (without granules).

Platelets: - (Thrombocytes.)
There are very small (2-3 m), non-nucleated, oval, biconvex disc like structures which secrete thromboplastin. Their number varies from 0.15 to 0.40 million/cu mm blood. During injury these get clumped at injured spot and release chemicals called 'Platelet factors' . These help in blood coagulaton.
Serum is blood without corpuscles & fibrin protein.

(ix) Lymph: - is translucent alkaline fluid present between capillaries and tissues. It contains plasma and.leucocytes.
Function: -Lymph carries materials from tissues into the blood stream and vice-versa.

1.3 MUSCLE TISSUE: - Muscle tissues are thin and elongated cells made up of diffetentiated cells containing contractile proteins.
Muscle cells are called 'Myocytes'.

Types: -Muscles are of three types: -Skeletal muscles, Cardiac muscles and Smooth muscles.

(a) Skeletal muscles: -These consist of bundles of very long cylindrical, multinucleated cells/ fibres (diameter 10-100 mm). Skeletal muscles are attached to bones by tendons. Each fibre has elastic outer covering 'Sarcolemma', cytoplasm called 'Sarcoplasm' filled and Myofibrils lying in the sarcoplasm. Each muscle fibre shows alternate light and dark bands called I-bands (Isotropic bands) and A-bands (anisotropic bands) respectively under light microscope. Each I-band has a dark membrane (Z-line) at its center.
Myofibrils are of 2 types-Thick filaments & Thin filaments.
Thick filaments occur in A-band only and are made up of protein 'myosin'. Their both ends are free.
Thin filaments occur in I-band butextend to some distance in A-band also. This partial overlapping of thin & thick filaments in A-band gives A-band a dark appearance. Thin filaments are made of protein actin, troponin and tropomysin. Their one end is attached to Z-line and the outer end is free.

(b) Cardiac muscle: -These are found in the wall of heart and large veins. Cardiac muscle consists of short, cylindrical fibres joined end to end and interconnected by oblique bridges forming a complex 3-dimensional network. They are mostly uninucleate, contain actin & myosin and show cross-striations. Intercalated discs are seen at places. These are specialized regions of cell membranes at the ends of adjoining cardiac muscle fibres forming dense junctions. Cardiac muscles can contract.

(c) Smooth muscle: -These are found in walls of hollow viscera. These are long (20 m-500 m), spindle shaped and have a single oval nucleus surrounded by sarcoplasm. There are fewer mitochondria and no striations. These can not contract voluntarily. Function: -These help in peristalsis.

1.4 NERVOUS TISSUE: -It forms the nervous system of animals. It has 2 types of cells-Nerve cells/Neurons and Glial cells. Neurons have many long processes and transmit nerve impulse. Glials have short processes and support the neurons.

Structure of neuron: -It has a cell body (cyton) and two/more cytoplasmic process (neurites) arising from it. Cell body varies in size & form. It has cytoplasm, nucleus and cell membrane. Nissl bodies/granules (rough endoplasmic reticulum with free ribosomes) are also present. Neurites are of 2 types:- Axons and Dendrons/dendrites. Axon is long and carries nerve impulses away from cell body. Dendron conducts nerve impulse towards cell body. Junction between axon of one neuron and dendrite of another neuron is called Synapse. Nerve impules pass between neurons through the synapse with the help of chemicals like Acetylcholine.

Types of Neurons: -
(a) Unipolar: -have only one axon and no dendron. Found in early embryos.
(b) Bipolar: -These have one axon and no dendron. Found in olfactory epithelium and retina of eye.
(c) Multipolar: -These have many processes arising from the cell body. Longest one acts as axon and remaining are dendrons. Found in brain and spinal cord.

Nerve Fibres: -Extended axons/dendrons of a neuron are called nerve fibres. Each nerve fibre is covered by neurolemma (made of Schwann cells).
Nerve fibres are of two types: -

Nerve Impulse : -Potential changes propagated along the membrane of the nerve fibre is called 'Nerve Inpulse' It carries message to neurons or muscles or glands.

MORPHOLOGY

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:56:00 +0000

Morphology is the study of general appearance and structure of an organism or its parts.
External Morphology deals with external features of an organism without dissecting it.
Internal Morphology deals with internal structure of an organism seen after dissecting it.
Animals are grouped as chordates and non - chordates. Earthworm & Cockroach are non - chordates. Frog and Rat are chordates.

1.1 EARTHWORM:-
Earthworms belong to phylum Annelida, Genus - Pheretima and species - Posthuma. There are about 500 sps. out of which 13 are found in India
(a) Habitat:- These are found in moist soil, living in upper layer to a depth of about 30 - 45 cm In dry climate, they come out on the ground

(b) Habit:- These are nocturnal, feed upon decaying organic matter in the soil, leave their faecal deposit as 'Warm Castings', dig their burrows and move by muscular contractions.

(c) External morphology:-

Shape:- Cylinderical, elongated, pointed arteriorly and slightly rounded posteriorly.

Size:- full grown worm is about 150 mm long and 3 - 5 mm wide

Colour:- Reddish brown. Dorsal surface is darker than ventral surface and has a dark median line

Segmentation:- Entire body has 100 - 120 segments / metameres Externally the segments are separated / divided by annuli & internally by Septa. Each annuli corresponds to a septa except the first four. This type of segmentation, which is both, external and internal is called 'Metameric Segmentation' or 'Metamerism'.

Mouth:- It is present at the anterior end of first segment 'Peristomium'. A small fleshy 'Prostomium' hangs over mouth.

Anus:- It is slit like opening in the last segment 'Anal segment' (Pygidium).

Female genital pore:- It is a small opening on ventral side of 14th segment. Eggs pass out of this

Male genital pores:- A pair of openings present on ventral side of 18th segment. Male reproductive fluid and sperms come out of this.

Nephridiopores:- These are numerous, very fine openings of excretory organs, scattered irregularly over all the segments except the first two.

Clitellum:- A band of glandular skin called 'clitellum' covers the segments 14, 15, 16. It secretes mucus and albumen which helps in fertilization. On the basis of clitellum, body of earthworm is divisible into preclitellar, clitellar and post - clitellar regions

Setae:- In all the segments, except first, last and clitellum, there is a ring of s - shaped setae which are made of chitin. These help in holding the substratum and during copulation.

(d) Internal Morphology:-

(1) The body wall comprises of cuticle, Epidermis Muscular layer and Peritoneum - Cuticle is thin, non - cellular membrane covering the entire body.
- Epidermis is made of single layer of columar epithelial cells and contains other cells also like secretory gland cells
- Muscle layer has circular & longitudinal muscle fibres
- Peritoneum lines the body cavity and secretes coelomic fluid. It is also called 'Parietal Peritoneum'.

(2) Digestive System:- It includes alimentary canal (tube like, runs from 1st to last segment), mouth (1st segment), buccal cavity (1 - 3rd segments), pharynx (4th segment), oesophagus (5 - 7th segment), gizzard (8 - 9th segment), Stomach (9 - 14th segment), intestine (15 - last segment) and anus (last segment). Gizzard grinds the food, stomach has calciferous glands which neutrilize humic acid. Dorsal wall of intestine has folds known as 'Typhlosole'.

(3) Circulatory System:- It is closed type. Blood is red. Blood glands are present on 4th, 5th and 6th segments. Haemoglobin remains dissolved in blood plasma.

(4) Nervous System:- Not very well developed. It is represented by ganglia (mass of nerve cells) arranged segment wise on ventral nerve cord. Nerve cord, in the region of 3rd & 4th segment bifureates to form Nerve ring. Nerve ring and central ganglia together form brain.

(5) Excretory System:- Main excretory organs are Nephridia. These can be septal nephridia (present on both sides of septa & opening into intestine), integumentary nephridia (attached on body wall living and opening on body surface) or pharyngeal nephridia (found in 4, 5, 6 segments as three paired tufts)

(6) Sense organs:- Poorly developed and represented by epidermal, buccal and photoreceptors.

(7) Reproductive System:- Earthworm is hermaphrodite. There are 2 pairs of testes (in 10th & 11th segments) and one pair of ovary (present at septum of 12th & 13th segments). Duct of testes ie vas deferens runs upto 18th segment. 4 pairs of sac like structures - sepermathecae are found, one in each - 6, 7, 8 & 9th segments. These receive and store sperms during copulation Development is direct.

Interaction with Mankind:-

(1) Earthworms make soil porous, enrich the soil and facilitate respiration and penetration of developing plant roots. So they are known as 'Friends of farmers'. The digested and decayed vegetation and fine soil is deposited by earthworm as 'worm castings'. The nitrogenous waste of the earthworm as added to soil. The process of increasing soil fertility by earthworm is called 'Vermicomposting'.

(2) These are used to cure piles, Jaundice, diarrhoea, bladder stones etc.

(3) Used as food

(4) Used as fishing bait

(5) Damage the land by making burrows & thus causing seepage and erosion.

1.2 COCKROACH:- (Periplaneta ammericana)

It belongs to class - Insecta, phylum - Arthropoda, genus - Periplaneta and species - americana
There are about 2600 sps in world

(a) Habitat:- Found in warm and damp places like sewage, pipes, kitchens, restaurants, bakeries, warehouses.

(b) Habit:- They are nocturnal & become active during night. These are cursorial ie run very fast. They feed on almost everything food, paper, leather, cloth, dead remains of other cockroaches

(c) External Morphology:-

Shape:- elongated, dorso - ventrally flat and bilaterally symmetrical body.

Size:- Males - 35 - 40mm long and about 10 - 12 mm wide females are slightly smaller

Colour:- Reddish brown

Exoskeleton:- It is formed of hard, brown chitinous plates called 'Sclerites'. Adjacent sclerites are joined by thin, flexible and soft 'Articular Membrane'.

Body division:- body is segmented externally and divided into three parts - head, thorax & abdomen.

(i) Head:- It is triangular and lies at right angle to long axis. It is formed by fusion of six segments. It can move due to flexible neck. It has mouth with appendages, sessile eyes, a pair of antenna. Mouthparts consists of mandibles and maxillae, labium (forms lower lip). Hypopharynx acts like tongue.

(ii) Thorax:- It has 3 ssegments - prothorax, mesothorax and metathorax. Neck connects head with thorax. Sclerites are present on thorax. There are 3 pairs of walking legs (one pair on each segment) . Each leg has 5 segments-coxa, trochanter, femur, tibia and tarsus. First pair of wings (Tegmina) arise from mesothorax.
Second pair of wings (Tegmina) arise from metathorax.
Tegmina are dark & leathery and cover the hind wings. Hindwings are transparent and are used in flight.

(iii) Abdomen: - Made up of 10 segments: In females, sclerite of 7th segment overlaps the sclerite of 8th & 9th segment.
7th sternum is boat-like and along with 8th & 9th sternum, it forms 'brood/genital pouch'.
Inmales: -7th segment overlaps 8th. 10th segment has a pair of jointed filamentous structures-Cerci. 9th segment has anal styles which is absent in females.

(d) Internal Morphology: -
(i) The body wall has cuticle (made up of chitin), epidermis (made up of single layer of columnar cells) and basement membrane (made of flat cells).

(ii) Body cavity is not lined by peritoneum and is filled with blood. So it is called 'Haemocoel'.

(iii) Digestive system is well developed. Alementary canal has 3 regions-foregut, midgut & hindgut. Mouth opens into pharynx which leads into oesophagus. Oesophagus opens into crop which is followed by Gizzard (Proventriculus) . Gizzard grinds the hard food particles. Mouth to gizzard form foregut. Midgut is tube like. Hepatic caeca which secretes digestive juices is present at junction of foregut & midgut. 150 malphigian tubules are present at junction of midgut and hindgut. Hindgut opens out by anus.

(iv) Respiration occurs by system of branching tubes the 'tracheae' which deliver oxygen directly to tissues. Tracheae open out by 10 pairs of spiracles (2 pairs lie in meso and metathorax, 8 pairs in abdomen).

(v) Circulatory system is open. There are no blood vessels. Heart is tubular and 13-chambered. Blood is colourless and called Haemolymph. It contains irregular, colourless corpuscles called Haemocytes.

(vi) Excretion is performed by Malphigian Tubules. Each tubule is lined by glandular, ciliated cells. They absorb nitrogenous waste product and convert it into uric acid which is excreted through hindgut.

(vii) Nervous system consists of series of fused ganglia joined by paired longitudinal connectives on the ventral sides. 3 ganglia lie in thorax and 6 in abdomen. Brain is represented by supra-oesophageal ganglion.

(viii) Sense organs are antenna, eyes, maxillary palps, labial palps and anal cirri etc. Antennae, palps and cirri are sensitive to touch. Compound eye consists of about 200 hexagonal ommatidia covered externally by transparent cornea. These receive several images of an object. This kind of vision is known as Mosaic Vision.

(ix) Reproductive System: -Males have a pair of testes lying one of each lateral side in 4-5th segment. Vas
deferens arises from testes and opens into ejaculating duct through seminal vesicle. An accessory reproductive gland is present in 6-7th abdominal segments. Male gonapophysis/phallomere is the external genitalia. Sperms are stored in seminal vesicle as bundles called Spermatophores. Female have 2 large ovaries lying in 4,5,6th segments. Each ovary has 8 ovarian tubules which contain chain of ova. Vagina opens into genital chamber.

Interaction with mankind: -
(1) Causes damage to household materials.
(2) Destroy the foodstuffs.
(3) Carries harmful germs of cholera, diarrhoea, T.B, typhoid.
(4) Serves as food.
(5) Used in experiments in laboratories.

1.3 FROG: -(Rana tigrina)
Frog belongs to phylum-chordata, sub-phylum vertebrata class Amphibia. Genus-Rana and species-tigrina. The most common frog found in India is Indian bull frog. Scientific name of common toad is Bufo melanostictus.

(a) Habitat: - Found in fresh water marshes, ditches, pounds and shallow lakes. Frog is called amphibious because it can live on land as well as in water.

(b) Habit: -They rest in squatting posture, are carnivorous, poikilothermous (body temp. changes with environment), swim, leap, make croaking sound for mating, breed in rainy season, undergo hibernation in winter and aestivation in summer.

(c) External Morphology: -

Form: -Frog has ovoid, slightly flattened body, streamlined for swimming in water.
Size: -Generally 18-20 cm long and 5-8 cms wide.
Colour: -dorsal skin is olive green with dark irregular lines and spots. Ventral side is pale yellow.
Body divisions: -Body is divided into head and trunk. Neck is absent.

(i) Head: -It is triangular, has mouth, external naris for breathing, eyes with eyelids, nictitating membrane for protecting eyes, Brow spot (light coloured spot in the median lines between eyes.)

(ii) Trunk: -It is flat and has a bulge called 'hump'. Trunk is divided into anterior small thorax and posterior large abdomen. Forelimbs and hindlimbs are present on the trunk. At the posterior end of trunk there is a small opening called 'Cloacal aperture' for eliminating faeces.

(d) Internal Morphology: -

(i) Skin: - It is olive green with pigments in it.

(ii) Body cavity is True coelom. It is lined by parietal peritoneum externally and visceral peritoneum internally.

(iii) Digestive system includes alimentary canal and digestive glands. Mouth opens into buccopharyngeal cavity which has many teeth. Eustachian tube, vocalsac and glottis open into buccopharyngeal cavity. Tongue is bilobed. Oesophagus is short. Stomach is tubular and is followed by small intestine (with folds called 'villi'). Intenstine continues into rectum which opens out by cloaca. `Digestive glands are Gastric glands (present in stomach, secrete intestinal juice), liver (secrets bile) and Pancreas (secretes pancreatic juice).

(iv) Respiration is pulmonary (by lungs), cutaneous (through skin) and buccopharyngeal. (v) Circulatory system is closed and consists of Blood vascular system and Lymphatic system. Blood vascular system comprises of Heart, blood vessels and blood, hymphatic system consists of lymph, lymph channels and lymph nodes. Heart is 3-chamibered and comprises of sinus venosus, two auricles, single ventricle and truncus arteriosus. RBCs, WBCs and leucocyctes and seen in the blood. Red-coloured pigment Haemoglobin is also present.

(vi) Nervous system has 3 divisions: Central Nervous system (brain & spinal cord), Peripheral nervous system (cranial & spinal nerves), Autonomic nervous system (sympathetic & parasympathetic system). There are 10 pairs of cranial nerves. Brain is enclosed in cranium. Brain is divided into Forebrain (olfactory lobes, cerebral hemispheres, diencephalon), Midbrain(pair of optic lobes) and Hind brain (includes cerebellum and Medulla oblongata).

(vii) Excretion occurs by a pair of bean shaped, red coloured kidneys. Each kidney has several uriniferous tubules/nephrons. Frog exeretes urea. Ureters coming out from kidneys open into cloaca.

(viii) Frog has 5 types of sense organs: - organs of Touch (sensory papillae), organs of Taste (Taste buds), organs of smell (nasal epitheluim), organs of vision (Eyes) and organs of Hearing (Tympanum and Internal ears).

(ix) Sexes are separate. Males have vocal sacs and nuptial pads which help in mating.

Males have a pair of testes attached to upper part of kidney by mesorchium. 10-12 vasa efferentia arise from testes and open into Bidder's canals present in the kidneys. Bidder's canals open into urinogenital duct which opens into cloaca and release sperms outside.
Females have a pair of ovaries which have their oviducts opening into cloaca. 2500-3000 ova are produced at a time. Fertilization is external. Development is indirect and has larval stage-'Tadpole'.

Interaction with mankind: -
1. Used as an experimental material for teaching & research.
2. Muscular legs of frog are used as food.
3. Small froglets are used as fish-bait.
4. It maintains ecological balance because it serves as food-link in ecosystem.

1.4 RAT: -(Rattus rattus)
It belongs to phylum-chordata, sub-phylum-vertebrata super class-Gnathostomata and class-Mammalia.
There are about 137 species of rat.

(a) Habitat: -Almost everywhere. It is found in holes and burrows in fields, indoors, hills, plains, rivers etc.

(b) Habit: -Rats are herbivorous, fossorial (live in burrows), nocturnal and undergo hibernation.

(c) External Morphology: -
Shape: -Body is elongated and covered with hair, tapered head, neck, slender trunk and long tail.
Size: -Adult rat is about 20 cms long.
Colour: -Colour varies. Rats living in open have bright colour coat whereas those living indoors have dull coat.
Body division: -Their body is divided into head, neck, Trunk and tail.

(1) Head: - It has nares (for respiration), mouth, eyes (with cyclids & reduced nictitating membrane), teeth, ears and tactile hairs called 'Pili tactiles' or 'Vibrissae' on both sides of nostrils.
(2) Neck : -It is short and connects head with trunk.
(3) Trunk: -Trunk has 2 forelimbs and 2 hindlimbs, anus & sex organs. Each limb is made up of stylopoduim, Zeugopoduim and autopoduim. Walking pads are present in palm. Anus is outlet situated at the base of tail. In females, urinary & genital apertures are located beneath anus & open separately into vulva.
In males , urinary & genital apertures open through urethra into penis.
In females, six pairs of nipples are present on the ventral surface of trunk.

(d) Internal Morphology: -

(i) Skin/Integument: - It has multilayered epidermis and a dermis. Outermost layer of epidermis is Stratum corneum & lowermost layer is Stratum germinativum. Dermis contains blood vessels, nerve fibres, receptors etc Glands like sweat glands, mammary glands are present in the skin.

(ii) Body cavity is true coelom.

(iii) Digestive system includes mouth which opens into buccal cavity. Food passes into pharynx. Oesophagus is short tube like and opens into sac-shaped. Stomach which leads into small intestine, S.Intestine has 3 parts-duodenum, jejunum & ileum. Ileum opens into caecum which opens into large intestine (colon). Colon leads into rectum which opens out through anus. There are 4 pair of salivary glands. Other glands are liver and pancreas.

(iv) Circulatory system is closed. Heart has 2 auricles and 2 ventricles. There is double circulation i.e. Oxygenated & deoxygenated blood circulates separately. Blood has RBCs (6-7 lac/cubic micro litre), WBCs (6-10 thousands/cubic micro litre) & platelets.

(v) Respiration is pulmonary. Lungs are spongy, lie in thoracic cavity and are lined by visceral pleura. Trachea is long.

(vi) Nervous system comprises of central Nervous system (Brain + Spinal cord) and Peripheral Nervous system. There are 12 pairs of cranial nerve and 33 pairs of spinal nerve. Brain is inside cranium. Autonomic nervous system comprises of chains of sympathetic & parasympathetic ganglia. Brain has large cerebral hemispheres and cerebellum.

(vii) Urinary system includes a pair of kidneys, ureters and a urinary bladder. Urine from kidneys passes through ureters and is stored in urinary bladder. Finally, it is carried out through urethra. In Males, urethra is common urino-genital passage. In females, urinary & genital tracts are separate.

(viii) Sense organs are Cutaneous (found in skin like tangorcceptors for touch, thermoreceptors for temperature, vibroreceptors for vibrations etc), Olfactory (for smell, present in epithelium of nasal chambers, jacobsons organs), Gustatoreceptors (for taste, found in tongue), Photoreceptors (eyes). Eye has cornea, iris, pupil, lens, eyeball, retina. Single image is formed on retina. Ear has 3 parts-pinna, middle ear & internal ear.

(ix) Male reproductive organs are pair of testes, epididymis, vasa deferens, urethra, penis & spermatic cord. Five glands-Ampullary, vesicular, prostate, preputial and cowper's are associated with male reproductive system. Sperms are produced in seminiferous tubules. Female reproductive organs are -pair of ovaries, fallopian tubes, uterus, vagina and clitoris. Three accessory glands - uterine, vestibular bartholins and preputial glands arer associated with reproductive system. Fertilization is internal, placenta is present and parental care is shown

Interaction with mankind:-
(i) Rat destroys fields by making burrows and tunnels
(ii) They damage 20% crop every year
(iii) They damage household goods also like books, clothes, food, vegetables etc.
(iv) It is a carrier of flea which spreads plague
(v) It is important component in food chain
(vi) Used in teaching & research
(vii) Used as an experimental animal to test drugs

Internal Structure of Angiospermous Plants

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:55:00 +0000

The plant body is made up of cells which organize themselves to form Tissues. Tissues organize to form tissue system. The study of the internal structure of plants is known 'Plant Anatomy'.

1.1 Tissue: -It is a group of similar or dissimilar cells performing a common function and having a common origin.
Types of tissues:-Two types -Meristematic and Permanent.

1. Meristematic Tissues(Meristems): -These are a group of cells which are in a continous state of division. These tissues divide to form new cells which differentiate to give rise to permanent tissues.

Types of meristems: -
A. On the basis of origin & development, these are of three types:
i. Promeristem: -It is a group of initial cells that lay down the foundation of an organ or plant part.
ii. Primary meristem: -It is formed from promeristem. Primary body, tissue differentiation and their organization' results from activity of primary meristem.
iii. Secondary meristem: -These are formed secondarily from permanent tissues which acquire the power of division.
B. Depending on their position in plant body, these are of three types:
i. Apical meristem: -Present at the tips of stem, root and their branches. Responsible for growth in length. It is dome like with outer layer-Tunica& inner mass-Corpus. It has promeristem which differentiates into three regions: -
* Dermatogen: -Outermost layer; gives rise to epidermis of the stem. In roots, it forms 'Calyptrogen' which is a mass of tissues which forms root cap. In dicots-it forms epilema of roots.
* Periblem: -next to dermatogen. Forms cortex of root and stem.
* Plerome: -lies internal to periblem. Cells elongate here and form procambuim which later forms Xylem & Phloem.
ii. Intercalary Meristem: -It is located in between the regions of permanent tissues. These cells divide and continue to add new cells. These are responsible for growth in length. Present at bases of node, internodes and leaves.
iii. Lateral Meristem:-These occur on sides & increase the girth of plant.

2. Permanent Tissues: -These are the tissues whose cells have lost the capacity to divide and attained a permanent shape, size and function.
Types:- 2 main types -Simple tissues & Complex tissues.
1. Simple Tissues: -are made up of structurally and functionally similar cells. They are of three types: -Parenchyma, Collenchyma and Sclerenchyma.
Parenchyma: -It is most abundant & common tissue in plants & is made up of similar isodiametric (all sides equal) cells. Cells may be oval, rounded or polygonal enclosing a large central vacuole and peripheral cytoplasm. Adjacent parenchyma cells are connected by Plasmodesmata. It forms cortex, pith, leaf mesophyll and floral parts.
Collenchyma: -Cells of this tissue contain protoplasm and are living. The cells are generally elongated with oblique end walls. Cell walls show localized thickenings due to the presence of pectin, cellulose and hemicellulose. These provide mechanical strength and elasticity to the plant.
Sclerenchysma: -It consists of thick-walled dead cells which vary in shape, size and origin. They have thick and hard secondary walls due to the deposition of lignin. These can be fibres or Sclereids. Fibres are pointed, needle like and occur in groups (as sheets or cylinders). Sclereids are thick, dead cells with narrow cavities. Cell walls have pits

2. Complex issues: -are the permanent tissues which contain more than one type of cells. These are of two types-Xylem & Phloem. Xylem & phloem, together are called Vascular Tissues.
A. Xylem: -It is conducting tissue, conducts water and mineral salts upwards from the root. It is of 4 kinds-Tracheids, Vessels, Wood fibres and Wood parenchyma.
Tracheids: -These are elongated dead cells with hard and lignified walls and a large cavity. Ends are tapering, blunt or chisel like. The walls have thickenings which can be annular, Spiral, reticulate, scalariform or pitted. These provide mechanical support and transport water, hormones and solutes from roots to stem, leaves and floral parts.
Vessels: -These are much elongated tubes with dead cells, lignified walls and a wide central cavity. End walls have simple (one pore) or multiple (many pores) performations. Found in majority of angiosperms, few pteridophytes & gymnosperms. Provide mechanical support to plant and transport water & minerals.
Xylem (wood) Parenchyma: -made of small thin/thick walled parenchyma cells having pits. It stores food, sometimes tannin and helps in lateral conduction of water/sap.
Xylem (wood) fibers: -These are sclerenchyma fibres associated with xylem. Can be septate/aseptate and may possess simple/bordered pits. These are mainly mechanical in function.
The first formed xylem is called 'Protoxylem'. It lies towards center of stem and has annular, spiral and scalariform vessels.
The latter formed Xylem is called 'Metaxylem'. It lies away from center and has tracheids with reticulate and pitted vessels.

B. Phloem:-Also known as 'Bast'. It is a conducting tissue which conducts prepared food from the leaf to the storage organs or growing regions of the plant. It consists of four types of cells:-Sieve tubes, campanion cells, phloem parenchyma and phloem fibres.
Sieve Tubes: -are long tube like structures associated with companion cells. Their end walls have performations (like sieve) and form a sieve plate. Later callose deposits here. They don't have nucleus but possess cytoplasm and a vacuole. Nucleus of companion cell controls its functioning. 'P-proteins'. (P-phloem) are present in the lumen of sieve tube which help in sealing a wound. Sieve cells replace sieve tubes in lower plants & gymnosperms.
Companion cells: -These are narrow, elongated and thin walled living cells lying on the sides of sieve tubes. These contain nucleus & cytoplasm. Its nuclei controls the activities of sieve tubes through plasmodesmata. Death of one results in death of another. Both are derived from same meristematic cells. These maintain pressure gradient in the sieve tube.
Phloem Parenchyma: -These are parenchyma cells associated with phloem. Their wall is made of cellulose, has pits, interconnecting axial parenchyma cells and ray cells. It stores food, resins mucilage, latex etc.
Phloem fibres: -(Bast fibres) -these are sclerenchyma fibres in phloem, occurs as sheets/cylinders, have pointed apex, thick cell wall with pits. At maturity, they loose protoplasm and die.
Protophloem: -It is the outer part of phloem containing narrow tube elements.
Metaphloem: -The inner part of phloem made of broader sieve tube elements.

1.2 THE TISSUE SYSTEM: -
Plants also have organized systems to perform functions. These are called 'Tissue System'. Sachs (1875) identified three tissue systems in plants based on morphological characters, development and function. These are:
A. Epidermal System.
B. Ground (fundamental) system.
C. Vascular (store/conducting) system.

A. Epidermal System: -It consists of: -
* Epidermis: -(epi-upon; derma-skin)-Outermost protective layer of plant organs, usually single layered, made up of compactly arranged living cells without intercellular spaces. Each cell has central vacuole surrounded by thin layer of cytoplasm. Root epidermis is called 'Epiblema'/Piliferous layer'. These have root hairs. Outer wall of epidermis is thick & covered by waxy 'Cuticle'.
* Stomata: -Epidermis of all green aerial parts of plant have minute openings called 'Stomata'. They are abundant in leaves (more on lower surface). In aquatic plants, these are more on upper surface. These are sunken in pits in xerophytes. Each stoma is surrounded by two live guards cells which have chloroplast. Their outer walls are thin and inner thick. Sometimes, guard cells are surrounded by less modified epidermal cells called 'Subsidiary Cells'.
Stomatal aperture, guard cells and subsidiary cells together constitute 'Stomatal Apparatus'.
* Epidermal Appendages: -e.g. Trichomes: -these are unicellular/multicellular epidermal outgrowths. Unicellular Trichomes are simple & unbranched.
* Root Hair: -These are unicellular structures formed due to elongation of epidermal cells. Found in Root Hair zone. Root hair cells have vacuolated protoplasm, nucleus lies in apical part of hair, wall is thin and pectocellulosic. They are short lived and help the plant in anchoring in the soil.

Functions of Epidermal System: -
- Provides protection to the plant parts.
- Cuticle checks the rate of water loss.
- Epidermal hair form insulating layer.
- Stomata take part in exchange of gases & transpiration.
- Trichomes help in seed/fruit dispersal.

B. Ground Tissue System:-It forms the main bulk of plant body, includes all tissues except epidermal and vascular and originates from periblem & plerome.In root and dicot stem, it has following parts: -
* Hypodermis: -Lies below epidermis. It is few layered thick madeup of collenchymatous/sclerenchymatous cells. It provides mechanical strength and rigidity.
* Cortex: -Lies between Epidermis/hypodermis and endrous. It is made of thin walled parenchyma cells. It is distinct in dicots but not in monocots. It stores food, performs photosynthesis (if chlorenchymatous), helps in retentation of gases (if aerenchymatous) and transfer of absorbed water & minerals to the interior.
* Endodermis: -Innermost layer, present between cortex and pericycle. It has tightly packed, barrel shaped cells without intercellular spaces. Waxy material 'Suberin' is deposited on the cells in the form of strips/bands called 'Casparian Strips' or 'Casparian bands'. It acts as check post between cortex and vascular strand.
* Pericycle: -It is multilayered & lies between endodermis & vascular bundles. In dicot stem, it encircles vascular bundle and pith like a cylinder. Made of parenchyma & Sclerenchyma cells. Absent in root & stems of aquatic plants.
* Pith (Medulla): -It is the central part of ground tissue and is often parenchymatous. It is well-developed in dicot stems & monocot roots. Intercellular spaces may be present or absent Stores food reserves.
* Medullary Rays: -Present between adjacent vascular bundles in primary structure of dicot stem. It is made of parenchyma cells and helps in lateral transport.

C. Vascular Tissue System:-It is formed by Xylem and phloem and their elements. These are arranged in bundles called 'Vascular Bundles'. In dicots, vascular bundles are open type i.e. Infrafascicular cambium is present between xylem and phloem. In monocots, cambium is absent and so vascular bundles are closed type.
Types: -Depending upon the arrangement of xylem and phloem, these are of two types-Radial and Conjoint.
1. Radial bundles: -Xylem and phloem alternate with each other. Mainly found in roots.
2. Conjoint bundles: -A vascular bundles, having xylem & phloem, both together. So both are at same radius. Mainly found in stem and leaves.
These are of 3 types: -
i. Collateral: -Phloem lies outside & xylem inside. It can be open or closed.
ii. Bicollateral: -Phloem occurs on outer side as well as inner side of xylem. Always open type & found in members of family Cucurbitaceae.
iii. Conjoint/Concentric:-A vascular bundle in which one type of tissue completely surrounds the another. It is of two types: -
Amphicribal:-Xylem is in the centre surrounded by phloem. e.g. Fern.
Amphivasal: -phloem lies in the center and is surrounded by xylem. E.g. Dracaena.
Position of Protoxylem in relation of metaxylem
Exarch: -Protoxylem lies towards periphery, Metaxylem towards center.
Endarch: -Protoxylem lies towards center and metaxylem towards periphery.
Mesarch: -Protoxylem is surrounded by metaxylem.

1.3 Internal Structure of Dicot and Monocot Plants: -

DICOT ROOTS: -e.g. young root of sunflower, pea or Gram. A transverse section of sunflower root shows: -
* Epiblema(Piliferous layer) : -Single layered, made up of living parenchymatous cells. A few cells elongate to form root hair. Cuticle & Stomata absent.
* Cortex: -Multilayered, present next to epiblema. It is made up of parenchyma cells with intercellular spaces.
* Endodermis: -It is single layered, made up of compactly arranged barrel shaped cells with no intercellular spaces. Radial walls of cells have casparian thickenings. Endodermis is usually considered innermost layer of cortex.
* Stele: -All tissues inside the epidermis form stele. These include pericycle, vascular bundle and pith.
Pericycle: -It is made up of thick walled parenchyma cells. It forms lateral roots or root branched.
Vascular bundles: -Radial type, Xylem has both, Protoxylem and Metaxylem. Xylem is exarch. Number of xylem & phloem bundles may be 2-6 (diarch to hexarch). Phloem & xylem bundles are separated from each other by one/more layers of thin walled cells called 'Conjuctive tissues'.
Pith: -Often absent. If present, it is quite small.

MONOCOT ROOT: -e.g. Maize.
T.S. of a monocot root shows: -
* Epiblema(Piliferous layer): -Outermost layer made of single row of thin walled cells. No intercellular spaces, no cuticle. Few cells elongate to from root hairs.
* Cortex: -Very wide region, made up of thin walled parenchyma cells with intercellular spaces. In older roots, epiblema dies off and few outer layers of cortex become cutinised and form exodermis.
* Endodermis: -Single layered consicting of barsel shaped cells with casparian thickenings. Few cells, present opposite to xylem, remain thin walled and are known as 'Passage Cells'. These transfer water and salts from cortex to xylem.
* Stele: -It is made up of one or few layers of parenchymatous cells and gives rise to lateral roots.
Vascular bundle: -Radial, Polyarch (many xylem & phloem bundles) and Exarch. Conjuctive tissue present.
Pith: -Very well developed. Made of parenchymatous cells. It stores food.

DICOT STEM: -e.g. Sunflower.
T.S of sunflower stem shows following structure:
* Epidermis: -Outermost layer, made up of compactly arranged parenchymatous cells. On its outer side, a thin layer of cuticle is present. Trichomes present.
* Cortex: -It has 2 parts-Hypodermis & general cortex.
Hypodermis: -just below epidermis. It is made up of 3-4 layers of collenchymatous cells. It has thickenings & chloroplast. Provides mechanical strength.
General cortex: -Consists of multilayered parenchymatous cells. Intercellular spaces and oil ducts present.
* Endodermis: -Innermost layer made up of barrel shaped cells which contain starch grains. So it is also called as 'Starch Sheath'.
* Pericycle: -Present between endodermis and vascular cylinder. It occurs as semilunar patches of sclerenchyma. Patch associated with phloem of vascular bundle is called 'Hard bast'.
* Vascular bundles: -Many vascular bundles are arranged in the form of a ring. Each vascular bundle is conjoint, collateral, endarch and open. It has xylem, phloem and cambium.
Phloem: -It is made up if thin walled polygonal cells and lies on outerside. It has sieve tube elements, campanion cells, phloem parenchyma & fibres.
Xylem: -Lies below phloem. It has vessels, tracheids, xylem parenchyma and fibres.
Cambuim: -Present between xylem & phloem. It has 2-3 layered thin walled cells.
* Medullary Rays: -These are parenchymatous areas between two vascular bundles.
* Pith: -Central part consisting of round parenchymatous cells with lots of intercellular spaces.

MONOCOT STEM: -e.g. Maize.
T.S. of maize shows following structure.
* Epidermis: -is the outermost layer of parenchymatous cells. It has a thick cuticle and few stomata.
* Hypodermis: -is present below epidermis and is made of sclerenchymatous cells.
* Ground Tissues: -It does not show distinction into cortex, endodermis, pericycle, pith and pith rays. Entire mass from hypodermis to the ventre is called Ground tissue and is made up of parenchymatous cells with inter cellular spaces.
* Vascular Bundles: -Many in number, oval in shape, conjoint, collateral, endarch and closed. Lie scattered in the ground tissue and each bundle is surrounded by sheath of sclerenchymatous cells called 'Bundle Sheath'.
Xylem is in the form of letter 'Y'. Two big oval metaxylem form divergent arms of Y. Protoxylem forms lower arm of Y. Water containing lysigenous cavity is at the end of protoxylem.
Phloem has sieve tube elements and companion cells. Phloem parenchyma is absent.

DICOT LEAF: -(Dorsiventral leaf)
V.S. (Vertical section) of a dicot leaf shows following: -
* Upper Epidermis: -is made of single layer of parenchymatous cells. Thick cuticle is present on outer side. Stomata, if present, are very few in number.
* Lower Epidermis: -is made of single layer of parenchyma cells covered by thin cuticle. Large number of stomata are present.
* Mesophyll: -Entire tissue between upper and lower epidermis is Mesophyll. It is differentiated into Palisade Parenchyma & Spongy Parenchyma.
Palisade Parenchyma :-Consists of 1-3 layers of vertically elongated, closely placed cells with little intercellular spaces. They have a vacuole, chloroplasts and perform photosynthesis.
Spongy Parenchyma: -have oval, loosely arranged cells with many air spaces/cavities which open out by stomata. Contain chloroplast. Perform photosynthesis and help in diffusion of gases.
* Vascular bundles: -Conjoint, collateral and endarch. Each vascular bundles is surrounded by Bundle Sheath(a layer of thick walled, compactly arranged cells). Xylem lies towards lower epidermis.

MONOCOT LEAF: -(Isobilateral leaf) .
A section of monocot leaf shows following: -
* Epidermis: -Single layered epidermis occurs on both the sides of leaf. It consists of compactly arranged parenchymatous cells. Cuticle is present on outer side. Equally distributed stomata are present on both sides. Bulliform cells (empty, colourless cells) are seen in grasses on upper surface.
* Mesophyll: -is made up of thin walled, parenchymatous cells with few intercellular spaces. Not differentiated into palisade & spongy parenchyma. Contains chloroplast.
* Vascular Bundles: -Conjoint, collateral, endarch and closed. Many vascular bundles are there, each surrounded by bundle sheath. Xylem lies towards upper side and phloem towards lower side.

1.4 SECONDARY GROWTH: -
Primary growth involves growth in length. Secondary growth is the formation of secondary tissues to increase the diameter. Secondary Growth is seen in most dicot stems and roots.
In DICOT STEM: -The process of secondary growth and structures associated with secondary growth are following: -
* Formation of Cambial ring: -In dicot stems, intrafascicular cambium is present between primary xylem and primary phloem. Secondary growth starts by formation of medullary ray. It is formed by division of parenchymatous cells of each medullary ray which become meristematic. Intrafascicular and interfascicular cambium join to form a complete ring of vascular cambium.
* Activity of Cambial ring: -Cells of cambium divide continuously. Out of the two cells produced from single cell, one becomes secondary tisues and other remains cambial cells.
* Formation of secondary Xylem & Secondary Phloem: -Vascular cambium has 2 types of cells: -Fusiform initials and Ray initials. Fusiform initials divide and ad new cells, both on inner side as well as outerside,. New cells on outer side form Secondary phloem. New cells on inner side form Secondary xylem. So xylem is formed more rapidly than phloem. Gradually xylem crushes primary & Secondary phloem of earlier years.
* Formation of Secondary medullary rays: -Ray initials divide and add new cells. New cells remain meristematic for some time & then differentiate into parenchymatous cells of rays. Secondarymedullary rays are formed by these cells in between secondary xylem & secondary phloem.
* Formation of Annual Rings: -Activity of cambium is affected by seasonal variations.
During Summer & Spring: -Temperature is high, relative humidity is high, duration of sunshine is long and new leaves supply hormones. These factors favour cambial activity, cells divide rapidly and several layers of undifferentiated cells can be seen. So large volume of xylem is produced which has larger, thin walled, light-staining components. It forms wood known as 'Early or Spring wood'.
In Winter & Autumn: -Temp. is low, sunshine is for lesser time. So cambial activity slows down. Lesser xylem is produced which has smaller, thick walled, dark-staining components. It forms wood known as 'Late or Autumn Wood'.
Spring wood has light colour and Autumn wood has dark colour. One light and one dark coloured zone forms an Annual Ring/Growth Ring. Each annual ring corresponds to the growth of one year. So age of plant can be easily calculated.
* Activity of cork Cambuim(Phellogen): -When secondary growth continues for many years, stem becomes thick. This may crack or break the outer tissues. To avoid this, plants develop a new cambium called 'Cork cambium/Phellogen' on the outer side.
Phellogen divides on its outer side and produces dead cells which form 'Phellem'. On inner side, phellogen divides and forms living cells which make 'Phelloderm'. Phellem (cork) + phellogen (cork cambuim) + Phelloderm (Secondary cortex) together form 'Periderm'.
Bark: -All the tissues outside vascular cambium form Bark. It includes secondary. phloem, elements of primary phloem, primary & secondary cortex in crushed state.
* Lenticels: -These are openings in the cork tissue which look like raised spots on surface of stem. Found in woody trees but not in climbers. There is a pore with loose mass of parenchymatous cells below it. This mass is called as 'Complementary Tissue'. These help in exchange of gases.
* Heart wood and Sapwood: -After certain years, older xylem becomes non-functional as it gets filled with oils, resins, gums, tannins, phenols etc. It becomes dead, darker in colour with lignified walled cells. This is called 'Heart Wood or Duramen'.
The outer young xylem which is lighter in colour and is functional is known as 'Sapwood or Alburnum'.

IN DICOT ROOT: -Secondary growth in dicot root is almost similar to dicot stem but the manner of formation of cambium & tissue differentiation differs.
* Formation of Vascular Cambuim: -
A part of cojuctive-tissue below phloem bundle becomes meristematic and divides to form brick shaped cells of cambium. This extends between xylem & phloem.
A part of pericycle above protoxylem also becomes meristematic and forms cambium. Both cambiums join to form a complete ring.
* Activity of Vascular cambium: -Cambial ring below phloem cuts off cells on inner side. Because of this overproduction, cambium & primary phloem are pushed outwards and so cambium ring becomes circular in shape. Entire cambium, now forms cells. Cells formed on inner side form secondary xylem. Cells formed on outer side form secondary phloem. Secondary tissues corresponding to each protoxylem bundle modify into parenchyma and form primary Medullary rays.
* Formation and activity of cork cambium: -Cells of pericycle become meristematic & form Phellogen. It divides on outer side to form Pheloem. Cells formed on the innerside consitute phelloderm. Lenticels are also present.

CHROMOSOMAL BASIS OF INHERITANCE

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:52:00 +0000

In heredity, genes are transmitted from parents to the off springs. Certain principles of genetics are followed in this. Genes are located on chromosomes. So, the genetic material is transmitted from one generation to the other by chromosomes. This is inheritance on the basis of chromosomes.
Sometimes genes present on same chromosome do not assort independently but remain linked together and pass on to next generation together. This is linkage.

(1.1) PARALLELISM BETWEEN GENES AND CHROMOSOMES:-
There is a perfect parallelism between genes & chromosomes which can be indicated by following facts:-
1 - Each species has a specific number of chromosomes in its somatic cell. In diploid cell, chromosomes occur in pairs (homologous pairs), one member of pair comes from paternal and other comes from maternal parent. Similarly genes also occur in pairs (Allelomorphic pair); genes in pair are contributed by both parents.
2 - During mitosis, the two chromatids of a chromosome separate into 2 daughter nuclei which later form 2 daughter cells. Similarly, each gene of allelomorphic pair goes into each daughter cell
3 - AT meiosis, chromosomes of each kind (homologous chromosome) separate. Similarly, genes of each kind also separate in meiosis
4 - Chromosomes unite & form a diploid pair after fertilization. Similarly, genes also form a pair after fertilization.

(1.2) CHROMOSOMAL THEORY OF INHERITANCE:-
According to this theory, chromosomes carry the hereditary information, possess Mendelian factors/ genes, seggregate & assort independently during transmission from one generation to next. So chromosomes are the vehicles of heredity.
Chromosome theory was proposed by Sutton and Boveri in 1902. It was later confirmed and expanded by Thomas H. Morgan, Alfred Sturtevant and Calvin bridges on Drosophila.
Chromosomes were seen in nuclei of Salamander cells by William Flemming in 1879.Salient features of chromosomal theory are:-
1 - Sperms & ovum carry all hereditary characters.
2 - Both, sperms and ovum contribute equally in heredity of offspring. Sperm provides only nuclear part to egg. This means, nucleus governs hereditary characters
3 - Nucleus contains chromosomes. There fore, chromosomes must carry hereditary traits
4 - Every chromosomes has a definite role in development of an individual. Loss of complete chromosome or a part of it produces deficiency in an organism.
5 - Both, chromosomes & genes occur in pairs in somatic or diploid cells.
6 - A gamete contains only one chromosome of a type and only one out of two alleles of a trait
7 - Paired condition of chromosomes & mendelian factors get restored during fertilization.
8 - Homologous chromosomes synapse during meiosis and then separate or seggregate independently into different cells.
9 - In many organisms, sex of an individual is determined by specific chromosomes called 'sex- chromosomes'.

(1.3) INDEPENDENT ASSORTMENT Vs. LINKAGE:-
Linkage is the phenomenon of certain genes staying together during inheritance through generations without any change or separation due to their being present on the same chromosome.
Thus Mendel's law of Independent Assortment is not universal and holds good for only those genes which are present on different chromosomes.
Linkage was first suggested by Sutton and Boveri(1902-1903). The genes present on same chromosome are called 'Linked Genes' and the genes present on different chromosomes are called Unlinked Genes' Morgan gave chromosomal theory of Linkage which states that
(a) Linked genes occur in same chromosome
(b) Genes lie in linear sequence in the chromosome
(c) There is tendency to maintain the parental combination of genes except for occasional crossovers.
(d) Strength of the linkage between two genes is inversely proportional to the distance between the two.

(1.4) COMPLETE AND INCOMPLETE LINKAGE:-
Linkage is of two types:- Complete and Incomplete
(a) Complete Linkage:- The genes located in the same chromosome do not separate and are inherited together to next generation because of no crossing over. This is complete linkage and parental traits are inherited as such. This is rare
Eg, A red eyed- normal winged (wild type) RRWW female Drosophila is crossed to recessive purple eyed- vestigial winged male, rrww
The progeny of F₁ generation is all heterozygous Red Eyed- normal winged (RrWw). When F₁ males are test crossed to recessive female (rrww), only two types of individuals are produced- Red eyed normal winged and purple eyed- vestigial in the ratio of 1:1 Recombinants are absent.

(b) Incomplete Linkage:- Crossing over occur in genes present in same chromosome. The genes remain incompletely linked, separate by crossing over and go to different gametes and off springs.
Eg, A red eyed normal winged dominant homozygous female Drosophila (RRWW) is crossed to recessive purple eyed vestigial winged male (rrww). F1 produced are heterozygous red eyed normal winged (RrWw). F1 females are test crossed with homozygous recessive males. It does not yield ratio of 1:1:1:1 but ratio comes out to be 9:1:1:8. Recombinants are produced.

(1.5) CROSSING OVER:-
Definition:- The phenomenon of exchange of genetic material between two homologous chromosomes is called as Crossing-over
The chromatids resulting from, exchange of segments are known as 'Cross- overs' or 'Recombinants'
Chromatids in which no crossing -over occurs are called 'Non-Cross overs' or Parental chromatids.
Janssens (1909) was the first person to discover chiasma formation and related process of Crossing over. Morgan used fruit fly Drosophila for his monohybrid and dihybrid crosses to deduce genetic information.
e.g. He performed a dihybrid cross between yellow body white eyed mutant female and grey body red eyed normal male. F1 females were all wild (normal) types and males had mutant characters. On crossing these females & males, F2 consisted of
98.7% yellow bodied white eyed files and wild files (Parental type ) 1.3% were yellow boded red eyed, and grey bodied white eyed (Recombinant type)
Recombinants were produced as a result of crossing over. Janssen observed chiasma formation during prophase I of meiosis I. Morgan proposed that chiasma are the points of crossing over.

(1.6) RECOMBINATION:- It is a meiotic process that results in a haploid product which is different in genetic constitution from both the parents. The product of recombination is called a 'Recombinant' Recombinants are formed by crossing over in Meiosis I. This can be explained by Chiasma -type hypothesis as follows.
1 - Synapsis :- During Zygotere of Prophase I, homologous chromosomes pair (synapsis). Each chromosome consists of two chromatids. The paired homologous chromosomes are called Bivalents'.
2 - During pachytene, two non- sister chromatids break & then rejoin.
3 - The rejoining occurs between non- sister chromatids thus leading to exchange of segments.
4 - Exchange causes reshuffling of genes and thus recombination occurs.

(1.7) CHROMOSOME MAPPING:-
Definition:- A chromosome map is a linear graphic representation of the sequence of genes on a chromosome and relative distances of various genes present on a chromosome. It is also called 'Genetic Map' or 'Linkage map'
Basis;- Based on 2 genetic principles

* The genes are arranged in linear order in the chromosome
* The frequency of crossing over between two genes is directly proportional to the distance between them on a chromosome. Closer the genes, lesser the crossing over. Farther the genes, more is the crossing over Relative distance between genes is indicated by percentage of their recombination or crossing over.

Map Units:- 1% crossing over between two linked genes is equal to 1 map units or 1 centimorgan (CM) in honor of T.H Morgan.

Preparation of a chromosome Map:-
e.g, Frequencies of crossing over or recombination between three genes- yellow body (y), white eye (w) and miniature wing (m) are:-
Yellow body- white eye: (y-w) 1.5%
White eye-miniature wing (w-m) 34.5%
Yellow body - miniature wing (y-m) 36.1%
Now what can be the order of genes? As genes lie in a linear order, so there distances should be additive let us put maximum frequency/ distance first.

(Distance between w-m automatically becomes 34.5)

Importance:-
(i) Gives exact location of genes on a chromosome
(ii) Indicates strength of linkage between two genes
(iii)Tells chances of crossing over between two genes
(iv) Predicts number of cross-overs
(v)Confirms the linear arrangement of genes on a chromosome

(1.8) SEX- LINKED INHERITANCE:-
In sexually differentiated organisms, a specific pair of chromosome determines the sex of an individual. These are called 'sex-chromosomes' or 'Allosomes' or 'Heterosomes'. All other chromosomes are called 'Autosomes'
In humans, males have XY and females have XX as sex chromosomes. Inheritance of a trait linked to sex- chromosomes is called sex- linked Inheritance.
e.g. Morgan studied a mutant allele which was located on X- chromosome in Drosophila. This mutant allele gave white eye phenotype (w) which was recessive to its wild type red eye(w⁺) allele. His results showed that inheritance of white eye was related to sex of parent carrying mutant allele. It can be explained by following cross.
(a) First Cross
(b) Second Cross:- (Reciprocal of first),

According to Mendel, both crosses should show similar results in F₁& F₂. But in the above two , results are different. Mrogan suggested that X- linked recessive allele shows criss- cross pattern of inheritance ie, recessive genes are transmitted from homozygous mothers to all male off springs.

(1.9) BASIS OF SEX DETERMINATION:-
Establishment of male or female individuals is called sex determination.
(i) Humans have autosomes (2A) and sex chromosomes. Females have 2A +XX, Males have 2A+XY.
Studies have shown that Y chromosome carries a gene 'sry' (sex-determining region) which codes for a product 'TDF' (Testis- determining factor). TDF is required for development of male sex. Its absence results in female sex. So Y chromosome determines maleness.
(ii) In Drosophila, work of Calvin Bridges tells that sex determining factor is number of X chromosomes /set of autosomes. Thus

-In 2A+2X or 3A+3X, ratio is 2/2 &3/3 which equal to 1.0. If ratio is 1.0, the sex is female and is fertile

-If ratio is more than 1.0 (3X+2A), sex is metafemale which is weak and infertile.
- 2A+XY and 2A +XO are males. 2A+XY are fertile. 2A+XO are sterile.

-When ratio decreases (e.g.3A+XY, ratio is 0.33), infertile metamales are produced.
- Flies with X/A ratio between 0.5 and 1.0 were 'intersexes' & had lots of abnormalities.

(iii) In birds & butterflies, male is ZZ and female is ZY. Female produces 2 different gametes instead of male as in above cases. So, egg, determines sex.

(1.10) GENETIC VARIATION:-
Whole set of characters are transmitted from parents to off springs. Still off springs look different from each other and from parents also. These are variations which occur due to recombinations, gene mutations, gene- environment interaction and chromosomal aberrations.

1 -Recombinations:- New combinations occur during independent assortment, crossing over and random fertilization of gametes. This results in reshuffling of genes & genetic variations.

2 - Gene Mutations:- Term 'mutation' was first introduced by Hugo de Varies in 1901 in plant Evening Primrose (oenthera lamarckiana)
Gene Mutations can be defined as sudden, random and discrete change in genetic material which is heritable. Most of the existing variations are due to gene mutations. Mutations occurring is germ cells are called 'Germinal Mutations' and those occurring in somatic cells are 'somatic Mutations'.
Mutations arising suddenly are called 'spontaneous Mutations'. When mutations are induced by certain agents then these are known as Induced Mutations. Agents inducing mutations are called 'Mutagens' e.g. radiations, chemicals.
Mutations cause variations which help in natural selection and thus lead to biological evolution. Geneticists study the modified genes & their transmission. Thus mutations provide 'Markers' which help in genetic analysis.

(a) Chromosomal Aberrations:- Alternation in chromosomes takes place in this. The structure or number of chromosome gets altered. So these are also called 'chromosomal Mutations'.

(i) Change in Chromosome structure:- Every living cell has a specific ser of chromosome with specific size & structure. Change in structure can occur by 4 ways- Deletion, Duplication, Inversion & Translocation.

Deletion:- A part of chromosome is lost either from end (terminal) or between ends (Interstitial ).
e.g. Cri-du- chat syndrome (cry of infant resembles sound of cat)- half of short arm of chromosome 5 is lost in humans.

Duplication- A portion of chromosome is repeated. It can be in tandem sequence or reverse order.
e.g. Development of bar eye in Drosophila.

Inversion:- In this, a segment of chromosome breaks, rotates at 180˚ and rejoins. When Centromere is included in rotated (inverted) segment, it is known as

pericentric inversion . When only arms are there in inverted segment & Centromere is not induded, it is called Paracentric inversion.

Translocation:- A segment of chromosome breaks off and rejoins a non- homologous chromosome. Chromosome suffering breakage becomes shorter and the other non-homologous chromosome to which the broken segment joins becomes longer than normal. This is simple translocation. In Reciprocal translocation, two non-homologous chromosomes exchange segments. So the chromosomes remain same in length but have rearranged gene blocks.e.g., In chronic myloid leukemia (CML), malignant cells have chromosome 22 shortened due to translocation of piece of its long arm.

(ii) Changes in Chromosomes Number :-
Every organism has a specific number of chromosome. Basic set of chromosomes for any individuals is called haploid (X). When 2 gametes unite, it produces an individual with double set of chromosomes called Diploid (2X). When change in chromosome number occurs, more than usual two sets of chromosomes are formed. This is called 'Polyploid'. Polyploids can be Triploids (3X), Tetraploids (4X), pentaploids (5X), hexaploids (6X) etc.
Polyploids are of two types- Autopolyploids (increase in number of same set of chromosome) and Allopolyploids (increase in number of same chromosomes of hybrids of different species).

e.g. of Autopolyploids - Maize, Rice, Gram.

e. g. of Allopolyploids- Wheat, cotton, Triticale(Man-Made)

When changes occur in an individual chromosome instead of whole set of chromosome, it is called 'Aneuploidy' and organism as 'Aneuploid'.
Aneupoploidy can be Hyperploidy (addition of chromosome) or Hypoploidy (loss of chromosome). Hyperploidy:- Trisomic (2n+1)-: It has 1 extra chromosome.
e. g. Down's syndrome (chromosome 21 is extra)
Tetrasomic (2n+2):– It has 2 extra chromosomes.
Hypoploidy:- Monosomic (2n-1) -:It has 1 less chromosome
Eg, Turner's syndrome
Nullisomic (2n-2)-: complete pair of homologous chromosome is absent. These don't survive.

Applications of Polyploids & Aneuploids:-
1 - Polyploids are used in crop breeding and horticulture.
2 - Allopolyploidy helps to pool genetic information from 2 different species to create a new species.
3 - Aneuploidy is used in crop engineering
4 - Aneuploidy is used to find roles of certain chromosomes in human development
(13.11) PROKARYOTIC CHROMOSOME:-
Chromosome of prokaryotes is long (approx 1.2 mm), lies in nucleoid which is a compact structure (as prokaryotes lack cell membrane), is made up of DNA and proteins.
Size of chromosome is long as compared to size of cell, so it lies coiled and super coiled.

(1.12) EUKARYOTIC CHROMOSOME:-
Chromosome of Eukaryotes is complex because of more number of chromosomes (46 in humans), more DNA/chromosome and large number of histone proteins. Length of 46 human chromosomes together is 2 metres. These lie in nucleus (size of nucleus-: upto 5 metres in diameter)
DNA associates with histone proteins to form Nucleosomes. (DNA is wrapped around histones , H1 histone lies outside DNA)
Chromatin fibre (10nm thick) condenses to form solenoid (30nm diameter) which coils to form chromatin fibre of 200 nm diameter and then a chromatid of 700 nm diameter.

(1.13) HUMAN GENETICS:-
The branch of genetics which deals with the study of inheritance of characters in man is called as 'Human Genetics'. Sir Archibald Garrod is regarded as 'Father of human Genetics'.
Human Genetics cannot be studied by breeding experiments as families are small & generation time is long. Various techniques are used to study it Pedigree analysis is one of the most important techniques. In this, a diagrammatic record of inheritance of a particular trait over two or more generations is maintained by using standard symbols. Then this record is analyzed. Transmission of a particular disease like albinism, Dwarfism, colour- blindness from parents to off springs can be found out by studying a pedigree

GENETIC DISORDERS:- After the rediscovery of Mendel's laws of Inheritance, human genetic analysis were done more extensively. Many genetic disorders were found in humans. In many cases, there was an error in a metabolic step which caused these disorders. Some disorders are :-

(i) Sickle- Cell Anaemia:- In this diseases, RBCs of the affected individuals become sickle shaped under low oxygen situation (Normal RBCs are biconcave). These individuals suffer attacks as RBCs aggregate in capillary system of venous side. Tissues also get damaged. This is called Sickle- cell crisis. Single pair of alleles Hb^A &Hb^s control it. Three genotypes are seen Hb^A/ Hb^A, Hb^sHb^s, Hb^AHb^s exhibiting sickle cell trait. Heterozygotes (Hb^A Hb^s) are carriers of defective gene.
These disease occurs due to substitution of value for glutamine at 6^th position is b-chain of globin molecule of Haemoglobin.

(ii) Phenylketonuria:- It is inborn metabolic disorder in which individuals lack enzyme to convert phenylalanine to tyrosine. So there is overproduction of phenylalanine which then accumulates in cerebrospinal fluid causing mental retardation.(some phenyl alanine changes to phenylpyruvic acid which comes out in urine).

(iii) Down's Syndrome:- (Mongolism or Trisomy-21).
First reported in 1866 by Langdon Down. It is due to imbalance is chromosome number or chromosome rearrangement. In it chromosome 21 is extra (Both the chromosomes of pair number 21 pass into single egg). Thus egg has 24 chromosomes instead of 23. Offspring then has 47 chromosomes instead of 46 (45+XY in males, 45 +XX in females)

Symptoms:- Small round head, protruding furrowed tongue, partially opened mouth, short broad hands, mentally retarded.

Note:- 1 chromosome is extra as paired homologous fail to separate at anaphase.

(iv)Alzheimer's Disease:- In this, memory and judgment ability is lost. There is physical impairment. Amyloid protein plaques accumulate in brain and degenerate the neurons causing this disease.

(v) Sex- Chromosomes linked genetic disorders:- Alteration in sex chromosomes is seen in these disorders which are:-

Turner's Syndrome:- (XO). Individual has 45 chromosome instead of 46. Formed by union of X sperm & abnormal O egg. or X egg and abnormal O sperm.
They are sterile females with rudimentary ovaries, undeveloped breasts, small uterus & abnormal intelligence.

Klinfelter's Syndrome:- (XXY). Individual has 47 chromosomes formed by union of XX egg & normal Y sperm OR normal X egg & abnormal XY sperm. They are sterile males with undeveloped testes, sparse body hair, long limbs & some female characteristics.

Super females:- Have 47(44+XXX), 48(44+XXXX), 49(44+XXXXX) chromosomes. Such females have abnormal sexual & mental development. More the number of 'X' chromosome, severe are the symptoms.

Super males:- Have 47 chromosomes with genotype XYY. There is overproduction of male hormones. These people are more aggressive, have unusual height, are mentally retarded with criminal bent of mind.

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Inheritance

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:49:00 +0000

There are different life forms which may be similar at cellular level of organization but at organismal level, a lot of diversity can be seen. Members of a particular species resemble closely & have a set of similar characters by which they are identified. Genetics deals with the study of these characters how these are passed on from one generation to another (ie, parents to offsprings)

(1.1) Inheritance: Heredity and Variation
Genetics (GK. 'genesis'-descent) is the branch of biology that deals with the study of heredity and variations. The term 'Genetics' was coined by William Bateson in 1906.
Offspring resemble their parents. This resemblances might not be 100% which means that difference among the members of a species can also be seen.
These differences shown by individual of a species and also by offspring of same parent are called 'VARIATIONS'.
The transmission of characters, resemblances and variations, from one generation to the next is called Heredity.

Heredity:-
So there appears to be a continuity of life which can be summed up in the phrase 'Like begets like'. Heredity & variation are also associated with the mode of reproduction. Higher forms reproduce sexually, there are two patents & character are received from both whereas in lower forms which reproduce asexually, characters are received from one parent only.

(1.2) Pre- Mendelian Ideas about inheritance
Many ideas were put forward before Mendel to explain the transmission of characters from parents to offspring's. They are often called as 'THEORIES OF BLENDING INHERITANCE' as they believed that characters of parents blended (got mixed) during their transmission to the offspring's.

(i) Vapour Theory:- Pythagoras (500 B.C) believed that each organ of body produces vapours which combine to form body part of embryo.

(ii) Fluid Theory:- Empedocles (504-433 B.C.) said that each body part produces a fluid, fluid from both parents mixes up 2 forms embryo. Any defect in mixing results in missing of characters.

(iii) Particulate theory:- maupertius (1689-1759) proposed that each animal produces minute particles for reproduction and a new individual is formed by union of particles of two parents.

(iv)Theory of Pangenesis:- Proposed by Charles Darwin in 1868. According to it, every part of the body produces a representative 'gemmule' which gets collected in semen by the help of blood circulation. These 'gem mules' theta transmitted the characteristics to the offspring's.
In 1892, August Wiseman rejected this concept and said that lining organisms consist of 2 types of materials- somatoplasm and germplasm. Somatoplasm makes the whole body, grows & develops & ultimately dies. Germplasm is immortal & is passed to next generation.

(1.3) Gregor Mendel and his theory of Inheritance:-
Gregor Jonann Mendel (1822-1884) is known as 'Father of Genetics'. In 1856, he observed the occurrence of two types of seeds in pea plant growing in his monastry garden at Brno. He started experimenting on these & gave some results in 1865 which went unnoticed. Meadel died in 1884 & his work was renoticed in 1900 independently by twice geneticists. They were Hugo de vries (Holland), carl correns of Germany & Erich von Tschermark of Austria.

MENDEL'S EXPERIMENT:-
Experimental Material:-
Mendel close garden pea (Pisum satervum) for his experiments. He chose this plant because-
1 - It had number of contrasting characters.
2 - It is small & easy to grow.
3 - It reproduces a large number of offspring's and completes its life cycle in one season.
4 - A large number of true breeding varieties are available
5 - It can be cross -bred manually
6 - It is bisexual & self fertilizing in nature.

Experimental Method:-

Mendel's experiment involved cross- breading of two pea plants with different contrasting traits. He noted 7 contrasting characters in pea plant which are-

S. NO	Characters	Dominant	Recessive
1.	Stem height	Tall (T)	Dwarf (t)
2.	Flower colour	Violet	White
3.	Flower position	Axial (A)	Terminal (a)
4.	Pod shape	Inflated/Full (I)	Constricted (i)
5.	Pod shape	Green(G)	Yellow (g)
6.	Seed shape	Round (R)	Wrinkled (y)
7.	Seed colour	Yellow (Y)	Green (y)

Mendel's experiment had 3 types:-

(i) Selection of pure parents:- All T characters noticed by Mendel were true-breeding i.e, were passed from parents to offspring's eg. Tall parent will give rise to a tall offspring. So, plants with these true characters formed pure parents (p) for next step.

(ii) Hybridization:- In this step, pure parents with contrasting characters like Tall & Dwarf, Green &yellow pod colour were crossed. Pollen grains from one type of plant. Were used to fertilize the egg of other. Offspring's in the form of seeds were collected. These seeds constitute next generation termed as 'FIRST FILIAL' orF1 generation.

Monohybrid Cross:- the cross in which two contrasting forms of a single character are taken into consideration eg. Height of plant (character). Tall or Dwarf (contrasting characters).

Dihybrid Cross:- the cross involving contrasting forms of two characters
Eg. Height and seed colour.

Trihybrid Cross:- cross involving contrasting forms of three characters.

(iii) Self- Breeding:- the plants of F₁ generation were allowed to self- pollinate. New seeds were produced which formed new plants. These were 'SECOND FILIAL' or F₂ Generation. Further self pollination produced 'THIRD FILIAL' or F₃

Results of the Experiments:-
Mendel first performed Monohybrid crosses and then Dihybrid. He considered single character-stem height contrasting pairs were Tall (T) & Dwarf (t). When two parents (Tall & Dwarf) were crossed, the F1 generation produced all tall plants.
When these F1 tall plants were self-crossed then out of total 1064 F2 plants, 787 were tall and 277 were dwarf. Many tall & dwarf plants were crossed and every time same results were seen. The ratio was 787:277 ie, 2.84 :1 or approx,. 3:1 (3 tall and 1 dwarf)
The results were same even when reciprocal crosses were performed. A Reciprocal cross involves the same trait but carried by sexes opposite to those in the original cross. Eg. In original cross, pollens from tall plants × stigmas from dwarf plant. In reciprocal cross:-
Pollens from dwarf plant × stigmas from tall plants

Mendel's Monohybride cross

The consist result obtained from different non hybrid crosses led Mendel to propose four postulates which are called 'PRINCIPLES OF INHERITANCE'.

POSTULATE 1. LAW OF UNIT OR PAIRED FACTORS:-
According to this law, the various characters are controlled by a pair of factors'. An individual receives one factor from each parent and thus has 2f. These factors are called 'Alleles' or allelomorphs'.
Eg, these are 2 unit factors for Tallness and 2 unit factors for dwarfness. So, these combinations are possible when these are crossed, either there are 2 factors for tall (TT) or two factors for dwarf (tt) or 2 factors- one from tall & one from dwarf (Tt).

POSULATE 2: LAW OF DOMINANCE:-
Each character has two contrasting factors which are called alleles. According to this law. Out of 2 alleles, one factor is able to express itself and the other is not. The one, which expresses itself is called 'Dominant unit factor' & the other which fails to express is called 'Recessive unit factor' eg, Tall is dominant & dwarf is recessive. These 'unit factors' are now called as 'Genes'.

POSTULATE 3: LAW OF SEGGRE GATION:-
According to this law, the factors of each character segregate (separate) during gamete formation so that each gamete receives only one factor for each character.
When tall & dwarf parents are crossed factors get segregated. Each gamete hill receive one factor, either tall or dwarf. When these gametes fertilize, F1 plants will have one factor for tall & one for dwarf but as Tall is dominant, so all F1 plants will be tall.

When F1 plants are self crossed, then again gametes will be formed. Factors will segregate and each ganete will receive factors rand only (either tall or dwarf).
On fertilization, which is a chance event, F2 generation will have 4 combinations of factors.
Tall/Tall. , Tall/ Dwarf, dwarf/tall, and dwarf/dwarf

Phenotypically, three will look tall (TT, Tt, Tt) and one will look dwarf (t). Ratio :3:1. Genotopically, one will be homozygous tall (TT), two will be heterozygous tall (Tt) and one will be homozygous dwarf (tt). Ratio 1:2:1

POSTULATE 4: PRINCIPLE(LAW) OF INDEPENDENT ASSORTMENT
According to this principle, the two factors of each character assort or separate' independently of the factors of other characters at the time of gamete formation and get randomly rearranged in the offspring.
The above can be explained by a dihybrid cross conducted by Mendel. He crossed plant with round &yellow seeds (RRYY) with plants producing wrinkled & green seeds (rryy). The F1 plants were all round & yellow (RrYy) according to law of Dominance (Round is dominant over wrinkled and yellow is dominant over green).
When F1 plants were self - crossed, Mendel noticed that one pair of unit factors segregates independently of the other pair of unit factors. This also means that these assort independently. During fertilization, factors distributed randomly & four combinations were produced.
9 yellow-round, 3 yellow-wrinkled, 3 green-round and 1 green wrinkled. Ratio :9:3:3:1

(1.4) GENETIC TERMS & SYMBOLS:-
F1 generation:- 'First filial. It is the generation of hybrids produced in a cross between two genetically different but pure parents.
Eg. F1 generation produced by crossing TT and tt parent plant has Tt individuals.
F2 Generation:- It is the 'second filial ' generation of young ones produced in a genetic cross between two F1 organisms
Reciprocal Cross:- It is a cross involving two types of individuals where the male of one type is crossed with the female of second type and vice-versa.
Back Cross:- A cross performed between hybrid and one of its parent.
Test Cross:- A cross between an individual and its recessive parent. This is done to find out whether individual is homozygous or heterozygous for dominant character

(1.5) METHODS OF ANALYSIS:-
PUNNETT SQUARE:-
It is a checker board type square devised by Regthald.c. Punnett (1875-1967) to show the results of a cross between two organisms. It tells both, genotype and phenotype, of a progeny.
In Punnett square, each gamete is placed in individual column, vertical column represents female & horizontal represents male parent. Possible combinations are made and entered in boxes.

TEST CROSS:-
It is a cross between F1 individual and a recessive parent to fine out whether as individual (F1) is homozygous or heterozygous for dominant trait.
In monohybrid cross, when F1 is test crossed, the ratio come out to be 1:1. In Dihybrid cross, when F1 is test crossed, ratio comes out to be 1:1:1:1. (It offspring is 100% dominant then it means F1 was homozygous dominant . If offspring are 50% dominant and 50% recessive, then F1 was heterozygous dominant)

(1.6) REDISCOVERY OF MENDEL'S WORK:-
Mendel started his work in 1856, presented for first time in 1865. But his work was not noticed for about 35 years because
- His ideas on heredity appeared too simple
-His algebraic (mathematical ) method of calculating combinations & was alien for other scientists.
&Wallace's continuous variations postulates
-At that time lot of emphases was on organic evolution.
In early twentieth centaury, hybridization experiments were performed independently by Hugo devoies, carl correns &Erich Tschermak. These were similar to Mendel's experiments. The results led to rediscovery of Mendel's work &science of Genetics.

(1.7) POST -MENDELIAN ERA:-
After rediscovery of Mendel's laws in 1900, geneticists started performing Mendel's experiments on other organisms. Many important principles & discoveries were made. These were described as Post-Mendelian Genetics.
Genes control the phenotype but sometimes the influence or interaction of other genes can alter the phenotype. Gene interactions can be of two types:-

(i) Intragenic:- Intractions between 2 alleles of same gene. It produces phenotype different from normal phenotypes. Eg. Incomplete dominance, co dominance, Multiple alleles.
(ii) Intergenic:- Interaction between alleles of different genes present on same or different chromosomes. These also after the phenotype. Eg, Epistasis, pleiothropy, Polygenes, complementary & Supplyementary genes, lethal genes

INCOMPLETE DOMINANCE:-
In this phenomenon, the F1 hybrid produced is intermediate or mixture of the two factors of parents. Dominant allele is not able to suppress recessive allele completely.
Eg. Incomplete dominance can be seen in Mirabilis jalapa (4'o'clock plant) and Antirrhinum majus (snapdragon).
In 4 'o' clock plant, there are plants with red flowers (RR) and with white flowers (rr). When the two are crossed, F1 produced are all pink (rr) flowered generation are of these types-Red, pink, white in the ratio of 1:2:1. pink colour appears due to incomplete dominance of red colour or mixing of red& white coloures.

CO- DOMINANCE:-
it is a phenomenon in which alleles do not show dominant- recessive relationship but express themselves independently when present together. Symbols used for co- dominant genes are different. These are capital letters with superscripts.
Eg. Alleles for blood group A (IA) and blood group B(IB) are co- dominant so that when they come together they produce blood group AB.

MULATIPLE ALLELES:-

Two alleles govern a character but three or more alleles can also be found. So, more than two alternate forms of a gene present on same touce are called 'Multiple alleles'.
These are formed when mutation occurs in same gene but different directions. Each allele produces different phenotype & different combinations of alleles also produce different phenotype.
Eg: 4 Blood groups in humans -A, B, AB, O. These letters represent antigens. 3 alleles -I^A, I^B, I^O - produce the above 4 phenotypes

Eg. Eye colour in Drosophila is also governd by multiple alleles.

(1.8) TWO GENE INTERACTIONS:-
These interactions take place between alleles of 2 different genes. Two gene interactions produce-
-Different phenotypes
-Homozygotes & heterozygoters governed by dominant allele.
-F1 indiciduals which are heterozygous for 2 gene pairs
-F2 genetypes in the ratio of 9:3:3:1.
Epistasis is the best example of gene interactions

EPISTASIS:-
Epistasis is the phenomenon of masking or suppressing the action of one gene by another non-allelic gene
The gene which masks the other gene is called 'Epistatic Gene' and the gene which gets masked is called 'Hypostatic Gene'.
Dominant or Recessive , any gene can mask the other.
Eg. Coat colour in Mice:- In mice agouti (grey) colour is dominant over black. Coat colour is determined by A/a pair (A-gives agouti, aa gives black phenotype). In B/b allele pair, recessive allele 'b' is epistatic over A/a. This means when bb is present, the effect of A- and aa gets masked and both produce the same phenotype with no colour ie, albino.

(1.9) POLYGENIC TRAITS:-
These are also called 'Quantitative traits'. These don't exhibit just 2 distant contrasting characters but show a wide range of phenotypes, usually controlled by more than one pair of gene(polygenes) and environmental factors.
The inheritance of polygenic traits is called 'polygenic inheritance'. In this kind of inheritance , F1 individuals are very similar to one another and intermediate between the 2 parents. On selfing F1, a wide variety of F2 is produced in which few individuals look like one grand parent few look like parent, few are intermediates.
Eg. Skin colour in Humans. It is controlled by three genes-A, B, C. A cross between pure Negro i.e, very dark (AABBCC) and a pure white cevery light (aabbcc) produces F1 with genotype AaBbCc with mulatto skin colour. On selfing F1 from 8 gametes in each sex thus producing 64 combinations in F2 generation.
Ratio is

1:	6:	15:	20:	15:	6:	1
Pure white:	Very light brown:	Light brown:	Mulatto:	Dark brown:	Very: dark brown	Pure black

(1.10) PLEITROPY:-
Generally, one gene controls one phenotype but in some cases , one gene may control several phenotypes. Such a gene with multiple phenotypic effect is called 'pleiotropic genes'. The ability of a gene to have multiple henotypic effect is called 'Pleiotropy'. Ex: In Drosophila, a single gene influences the size of wings, character of balancers, position of dorsal bristles eye colour, fertility, longevity
Eg: In humans the gene which causes the disease sickle cell Anaemia also alters the type of Haemoglobin & changes the form of RBC.

Understanding Life

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:47:00 +0000

INTRODUCTION: Some organisms are living e.g. Bacteria, animals whereas some organisms are non-living. e.g. bricks ,stones. The main difference between the two is of ‘life’. Defining ‘life’ is difficult. Example of virus supports it. A virus doesn't have a life but when it is inside a cell, it becomes active and multiplies showing that it has life.

(1.1) ORGANISMS SHARE SOME BASIC AND UNIFIED CHARACTERISTICS :
Living organisms differ from each other in many aspects but they have many things in common like all are built up of cells, which have same structure and function. All have same basic characteristics governed by same physical laws like order, energy utilization, regulation, growth, development, reproduction etc.

Common feature of living organisms:
* Have fixed shape and size.

* Are highly organized. It is because of this organization that living being is called ‘organism’. Cell is the basic structure of organization and there are different levels of organization.

* All show metabolism i.e. series of biochemical reactions keep going inside cell. Reactions involving breakdown of compounds are ‘catabolic reactions. Reactions involving synthesis of compounds are ‘anabolic reactions’.

* Use energy for metabolism and growth.

* Show development and reproduce.

* Maintain constant body temperature (Homeostasis)

* Adapt to environmental changes.

* Gradually evolve into new species.

(1.2) ANALYSING THE LIVING THINGS :
All living organisms have organized structure. Lower organisms have simpler
Structure and higher organisms have complex structural level. Plants don’t have similar organization as that of animals.
Levels of Biological organization: Organization can be defined as the manner in which smaller units are arranged into larger ones and each level co-ordinates with each another.
In living organisms, lowest unit of organization is ‘Atom’. Atoms combine to from ‘Molecules’. Molecules undergo chemical reactions and form ‘organelles’ which are contained in a ‘Cell’. Organisms can have single cell (unicellular) or many cells (multicellular). Group of cells performing common function is ‘Tissues’. Many tissues combined together form ‘Organs’ (stomach, lungs). Many organs together, performing a specific function forms ‘Organ System’ (e.g. digestive system). Such living things with higher levels of organization are called ‘Individuals/ Organisms’. Group of individuals, which can interbreed sexually form ‘Species’. Group of organisms belonging to same species forms ‘Population’. Population of different species in an area is ‘Community’. Community with its abiotic (non-living) environment forms ‘Ecosystem’. All the ecosystems of world interact and form ‘Biosphere’.

Molecular organization: A shift in approach
In early days, when techniques were not advanced, the knowledge of living organism was based only on its morphology. But now, when scientists have advanced techniques, they study finer details of organism up to molecular level. Their observation tells-
-Basically, all living organisms are made up of similar atoms and molecules.
-Life is governed by same physical and chemical laws as seen in non-living things.
-There is interaction between living things of Biosphere and non-living things in land, water and air.
All living and non-living things are made up of matter. ‘Matter’ is something, which has, mass and occupies space. It is made up of atoms. Similar atoms form ‘Elements’. There are more than 100 elements in nature. 25 are essential to life. Six elements (C, H, O N, P, S) form 98% of the mass of living organism. Other elements are required in small amounts and are called ‘Trace Elements’ (K, Ca, Mg, I, Na). These are also very important e.g. Iodine is very important for normal functioning of Thyroid gland.

Chemical bonds:
Covalent Bond – Two or more atoms link together to form a molecule. The linkage is due to chemical bonds. When pair of valence electron is shared between two atoms, it forms covalent bond.
If single electron pair is shared    – Single bond e.g. H-H
If two electron pair is shared     - Double bond e.g. O=O
If many electron pair is shared    - Multiple bond e.g. in CH₂

Hydrogen Bond – when molecules show separate charges, these are called ‘Polar molecules’. e.g.H₂O (water). It has two atoms of hydrogen and one atom of oxygen. H has positive charge and O has negative charge. In liquid water, negative oxygen atom of one water molecule is attracted to positive hydrogen atom of another water molecule. This force of attraction is called Hydrogen bond. It is a weak bond and has only 10% strength of a covalent bond. Weak H-bonds are very important in biological systems because:
--Contact between molecules remains brief.
--Molecules separate after interacting.
Importance of weak H- bonds can be explained by a situation- Transmission of chemical signals to molecules in brain. Molecules send signals to brain using weak bonds. After this, they separate (because of weak H-bonds). Receiving cells in brain receive signal and initiate reaction.
If, there is a strong covalent bond instead of weak H- bond, the receptor cells will keep responding for a long time even after the signal cells have stopped sending signals (because strong bond will not let them separate faster.)

Ionic Bonds: Ions are charged particles when atom gains/ looses electrons to attain stability. Ions with positive charge are called cations. Ions with negative charge are Anions. A bond formed due to attraction between these two oppositely charged ions is known as Ionic Bond.
e.g. in NaCl   , Na atom has 11 electrons ( 2 in inner energy level, 8 in next level and 1 in outermost i.e. valence level). It is unstable because of unpaired outer electron. To become stable, it should loose this electron and then it becomes positively charged ion i.e. Na+.
Cl has 17 electrons (2 in inner energy level, 8 in next and 7 in outermost valence level). To become stable, it should gain 1 electron to make total of 8 electrons. In doing so, it becomes a negatively charged ion i.e. Cl‾ .Electro negativity of Cl atom is more (3.1) than Na atom (0.9), so electrons will be closer to Cl nucleus. Na donates electrons to Cl forming Na+ and Cl^- ions, which link by ionic bond to form NaCl crystals.

Importance of NaCl: -
(i) It is given as saline drip to patients with low B.P. as it retains water in body.
(ii) Na+ and Cl^- help in transportation of materials into cell membrane.
(iii) Na⁺ is important for conduction of nerve impulse.
(iv) NaCl maintains R.B.C.
(v) Cl^- are important constituents of blood plasma.

Water is cradle of life- It is the only molecule existing as liquid at low temp.
Importance of H₂O :-

* 70-80% of cells and 70% of human body is made up of water.

* Life originated in water and evolved in it for 3 billion years.

* It speeds up metabolic reactions.

* In most biochemical reactions, water is either substrate or product.

* It maintains turgidity of cells.

* It is a natural solvent for most nutrients. This can be explained by dissolving salt in water. H₂O molecules form H-bond very fast. They gather around charged molecule (NaCl). The electrical attraction of H₂O molecule breaks the forces/ bond between Na+ and Cl‾. Then it forms H-bonds around individual Na+ and Cl‾ ions, forming Hydration Shell around each so that they cannot reassociate.

Carbon :-
It is the main structural element of the cell. Source of C is inorganic CO₂. Our atmosphere has only 0.003% of CO₂. To take part in a chemical reaction, it should dissolve in water. All cells have film of water, which is enough to dissolve CO₂ and form Carbonic acid.

Oxygen :- It is essential for life .Our atmosphere has 21% of oxygen.

Importance of oxygen:
* Most animals and plants need O₂ to get energy.

* It accepts electrons.

* Efficiency of cell decreases in absence of O₂ (are only 5% efficient of their normal efficiency)

* It is weakly soluble in water but for aquatic organisms, this small amount of O₂ is enough.

Building Blocks of Life :- All the living organisms are made up of C, H ,O and N. These elements can group to form smaller molecules called ‘Micro molecules’.
Micro molecules can group further to form a bigger molecule called ‘Macromolecule’. Life depends on both the molecules.
e.g. Micro molecules – water , salt , sugar.
Macromolecules- Lipids, Proteins etc.

* Carbohydrates – These are compounds containing C, H & O in the ratio of 1: 2:1. These can be sub-divided into –

* Monosaccharides- (single sugars) these are simple sugars. e.g. Glucose

* Disaccharides- (double sugars) When two monosaccharides join by bonds, they form disaccharides. e.g. Sucrose, Lactose.

* Polysaccharides- when many monosaccharides join, they form polysaccharides. e.g. Starch, Cellulose. These molecules join by C-H or C=O bonds, which store a lot of energy. When these bonds break, energy is released. So these are ‘energy storage molecules.’

* Lipids – These are the esters of fatty acid and alcohol. Lipids:-

* Have –COOH group (carboxyl).

* Are hydrophobic i.e. insoluble in water.

* Are soluble in organic solvents like ether.

* Act as shock absorbers of the body.

* Provide insulation.

* Store a lot of energy.

* Form structural element of cell membrane e.g. phospholipids.

* Act as hormones e.g. Steroids.

* Constitute biological pigments. e.g. Chlorophyll.

* Act as local chemical messengers in the cell. e.g. Prostaglandin

* Proteins- is made up of amino acids, which have amino group (-NH₂) and a carboxyl group (-COOH). There are 20 different amino acids which link by peptide bonds to form proteins.20 different amino acids can arrange in any sequence. Amino acids are also called ‘Peptides’, so when many peptides link together, we call it as ‘Polypeptide chain’ also. Proteins are formed of many polypeptide chains.

Proteins-
* Are structural and functional components of the cell.

* Collagen in bone cells is made up of proteins.

* Helps in muscle contraction. e.g. Actin, Myosin.

* All enzymes are proteins.

* Help in defense system of the body e.g. Antibodies which fight diseases are proteins.

* Act as oxygen transporters. e.g. Hemoglobin.

iv) Nucleic Acids – are also called as ‘Polynucleotides’. Many nucleotides join together by phosphodiester bonds. Each nucleotide contains-

(1.3) ENERGY TRANSFER DEVICES OF LIFE :
Energy is the capacity to do work and is essential requirement of all the organisms. All the activities like growth, transport etc. going on in the cell need energy. Cells cannot manufacture energy on their own but get it from outside. Then they transform (change) it into the form in which they need it.
e.g. .In Plants, they take solar energy and transform it into chemical energy for their activities.
E.g. In Animals, they take food from outside and break it down to release energy.
Energy Flow takes place through chemical reactions. In chemical reactions, electrons are transferred from one atom to another. Energy is captured in the electrons. When electron is lost, reaction is called ‘Oxidation’. When electron is gained, reaction is called ‘Reduction’.

Enthalpy: The total energy in the biological system is called ‘enthalpy’. It includes the usable energy as well as the unusable energy. Usable energy is used for performing work and unusable energy is lost to disorder.

Free Energy: The amount of usable energy, which can perform work at constant temperature and pressure, is called ‘Free energy’.

Activation Energy: The minimum amount of energy required to initiate a chemical reaction by destabilizing the bonds is called ‘Activation Energy’.

Spontaneous Reactions: Reactions, which occur on their own, release energy and perform work, are ‘Spontaneous reactions’.

Exergonic reactions: Reactions, which release energy and do not need energy from outside, are called ‘Exergonic Reactions’.

Endergonic Reactions:  Reactions, which require energy from outside to start are termed as ‘Endergonic Reactions’.

Energy Flow: Chemical reactions are important for constant flow of energy. Energy can neither be created nor destroyed but can be changed from one form to another (energy transformation). All daily activities like running etc. involve energy transformation. This energy change is explained by LAWS OF THERMODYNAMICS.

First law of thermodynamics- The total amount of energy in the universe is constant. It can neither be created nor destroyed but can be changed from one form to another.
Explanations:-
a) In plants,

Second law of thermodynamics- For any process, physical or chemical to occur, there is increase in entropy (disorder) and decrease in free energy of the system.
Explanation: - This is because energy flows from higher energy area to lower energy area. During this, molecules collide, which increases disorder. When disorder increases, energy is lost in the form of heat, which cannot be restored.

Open System: Systems in which materials and energy are freely exchanged with the surroundings.
e.g. Living organisms. In living organisms, energy and materials are freely exchanged between cells and surroundings. If this will not happen, entropy will increase and organism will die.

Closed System :  Systems in which materials and energy are not exchanged with the surroundings.
e.g. Non living materials like Thermos Flask.
In Thermos flask, exchange cannot take place with the surroundings. So energy remains same for a certain period of time (depending upon the efficiency of flask) and liquid remains warm.

(1.4) METABOLISM : All living things need continuous supply of energy and materials. Energy keeps flowing from one cell to another and from one organism to another. Metabolism can be defined as sum total of all the chemical reactions, which occur due to molecular interactions in a cell of an organism.

Enzymes – A catalyst is a substance that speeds up a chemical reaction but remains unchanged itself at the end of the reaction. Cells also require catalysts for specific reactions. These specialized catalysts are called as ‘Enzymes’. An organism has thousands of enzymes. Reactions in a cell occur in a sequence called ‘Biochemical pathway’. A particular enzyme acts on a particular substrate. Most enzymes are protein molecules with pockets on their surface. These pockets are called ‘Active Sites’ and a particular substrate binds here. Enzyme-Substrate complex is formed which forms products.

Regulation of Biochemical Pathways:
Anabolic reactions and catabolic reactions never occur simultaneously otherwise there would be chaos. Lot of energy and material would be wasted. Cells have regulatory system to control biochemical reactions. All biochemical reactions need enzymes, which bind to particular substrate. Activity of enzymes depends upon specific substances also which bind to it. A substance which binds and decreases its activity is called an ‘Inhibitor’. A substance which binds and increases the activity is called an ‘Activator’.
In a biochemical pathway, product of one reaction can serve as substrate for next reaction. So, enzymes selectively accelerate a reaction when necessary. The product itself becomes an inhibitor and stops enzyme activity. This regulatory mechanism is called ‘Feedback Mechanism’. (Enzymes have active sites where substrates attach& have ‘allosteric sites’ where an inhibitor attaches. this inhibitor then changes the shape of active sites and enzyme cannot bind to the substrate and the reaction stops.) So, regulation of biochemical reaction depends upon allosteric site of an enzyme.

Homeostasis :
Organisms need to maintain a constant internal condition so that biochemical reactions go on. They themselves regulate and adjust to the fluctuations in the external environment. So, such a self-regulated mechanism of maintaining a steady internal environment by an organism despite changes in external environment is called as ‘Homeostasis’.
e.g. Vigorous exercise raises the body temperature. Sweating brings it back to normal.

Thermoregulation:
Regulation of body heat by an organism is called Thermoregulation.

* Some animals like vertebrates and plants loose their thermal energy to the environment. Such animals are called ‘Ectothermic animals’. They are also called ‘Poikilothermous’ as they depend upon environment for its temp. regulation. If their environment is warm, their skin will be warm. If environment is cold, their skin will be cold.

* Some animals like mammals, birds, fish don’t loose but retain their thermal Energy for use. These animals have fats, feathers, furs, hairs etc. which act
as insulators. Such animals are called ‘Endothermic’. They are also called As ‘Homeothermous’ as their body temp. remains constant. If outside is very cold, their superficial vessels contract and warm blood stays in deeper vessels. If outside is very hot, the superficial vessels dilate and extra warmth of blood is lost by radiation.

Homeothermy in Humans:
Humans are endothermic and homeothermic. Their constant body temp. is 37 degrees Celsius. Our skin has two types of sensory neurons, which are sensitive to temp. outside. These are called ‘Thermoreceptors’and occur in skin and brain.

In brain- Receptors are present in hypothalamus. These monitor blood temp. and send message to brain whenever there is change in temperature.
How thermoregulation works: It can be explained with the help of example below:-

This is called negative feedback loop because temperature is regulated by negative reaction i.e. cooling of the body.

(1.6) GROWTH, DEVELOPMENT AND REPRODUCTION :
All organisms grow, develop and reproduce. Growth is the result of metabolic reactions. Energy transfer takes place. If rate of anabolism is more, growth occurs. If rate of catabolism is more, degrowth occurs. If anabolism is equal to catabolism, no growth occurs.
So, Growth is increase in mass/overall size of an organism.

Growth is a part of development.

Reproduction is the production of similar copies of an organism. It is necessary for continuation of life. Organisms reproduce sexually as well as asexually.
In sexual reproduction, there are sperms (male sex cells) and ova (female sex cells).
Asexual reproduction can occur by Binary fission, multiple fission, fragmentation etc.

(1.7) ADAPTATION:
It is the characteristic of an organism, which makes it better suited to its environment. When organism possesses inherited features, which increase its survival and ability to reproduce, they are best adapted. Adaptation can be structural, physiological and behavioral. These can be temporary or permanent.
E.g. (i) Narrow and elongated beak of Humming Bird: -
This helps the bird to suck flower nectar without sitting on them as there is
no place to sit.
(ii) Shapes of Orchids: -
Some orchids have shapes like female bees or female flies. So male flies/bees get attracted to it and try to copulate. In doing so, they transfer pollens from flower to flower.
iii) Night flowers are white to attract insects.

(1.8) DEATH :
Death is a permanent feature of all living organisms. A living organism is born as a young one, grows in size, becomes adult, reproduces its own kind. Undergoes ageing, grows old and ultimately dies.
Significance of death: -
i) It maintains balance in population thus avoiding overcrowding.
ii) It maintains biological cycle because when an organism dies, it increases organic matter. Decomposers attack organic matter, break complex organic matter into simpler forms which further transform into inorganic C, H, O, N, S, P by mineralization. These, then return to soil.
iii) Some dead cells or derivatives are important structures of body. e.g. nails, horns, hooves, claws etc.

SYSTEMATIC

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:43:00 +0000

There are more than 10 million kinds of living organisms like animals, plants, bacteria, viruses which are different from one another. Out of these, nearly 1.2 million animals and 0.5 million plant species have been studied. Many are still unknown. To study and remember each species is practically not possible. So, to make this simpler, Biologists name them. They use techniques for identifying, naming and grouping of organisms.

(1.1) BIOLOGICAL CLASSIFICATION: --
To pick an organism of known characters from a huge variety of living organisms is not possible. They must be divided into groups and sub-groups with each having organisms of almost similar characters.
Definition- The scientific ordering of organisms in hierarchical series of groups/ sub-groups on the basis of similarities/ differences and their relationships is called Biological Classification.

Objectives of biological classification -:
1.to organize vast number of animals and plants into categories and then naming them.
2. To recognize basic unit of classification i.e. Species.
Advantages of Biological classification: -
1.It makes identification and study of organisms convenient.
2. It shows relationships among various groups of organisms.
3. It shows evolutionary trend.
4. Study of a representative from each group gives a broad idea about whole group.
5. It helps in study of fossils for finding evolutionary relationships.

Systematics/ Taxonomy (Gk.words) Systema-order. (taxis-arrangement nomos-law)
Given by de Candolle in 1813. Deals with the identification, nomenclature and classification of organisms.
Some scientists consider Systematics and Taxonomy as separate fields. According to G. Simpson (1961), Systematics is the study of diversity of organisms and all their comparative and evolutionary relationships based on comparative anatomy, ecology, physiology and Biochemistry. Whereas Taxonomy is the study of principles and procedures of classification. And Classification is the sub-topic of systematics dealing with ordering of organisms into groups. But all these terms are inter-related and so inter-changeable also.

(1.2) HISTORY OF CLASSIFICATION: - Plants and animals existed before man evolved. But man was advanced species, so he started using plants and animals for its needs and even classified them in its own language.
--According to Vedic literature (2500 BC-650BC), there are 740 plants and 250 animals.
--While Chandayoga Upanishad classifies animals only
--Susruta Samhita (600BC), a post-Vedic Indian literature classifies

Theophrastus gave names and descriptions of 480 plants in his book ‘Historia Plantarum’. John Ray (1625-1705) described more than 18,600 plants and animals in his book
Carolus Linnaeus (1707-1778) is the ‘Father of Taxonomy’. He published book ‘Systema Naturae’ in 1758, classified and arranged 4000 plant species on the basis of sexual characters in his book ‘Species Plantarum’ (1753). He gave system of Binomial Nomenclature’ according to which a scientific name has two parts- Genus and
Species. E.g. Homo sapiens. Homo is genus and sapiens is species.

Types of Taxonomy: -
(1). Numerical Taxonomy: - (Phenetics) emerged since 1950.It uses numerical methods for evaluation of similarities and differences between the species. It is based upon proposals of Adanson (1763), that for classification, as many characters as possible must be taken, without extra emphasis on any particular character and all factors are given equal importance and weightage. As numerical Taxonomy is based on these principles, it is also called as Adansonian Classification. A family tree based upon phenetic classification is called Dendrogram.Computers and calculating machines are used in this method.
(2) Phylogenetic Classification (Cladistics) - It classifies organisms according to the historical order in which evolution occurred. It led to emergence of ‘New Systematics’(Huxley 1940)/ Biosystematics.
Cytotaxonomy :-It classifies organisms on the basis of information about cell like cell Structure, chromosome number, behaviour of chromosome during mitosis and meiosis etc..
(4) Chemotaxonomy :-It classifies organisms on the basis of its chemical constituents like amino acids, carbohydrates, alkaloids, calcium oxalate crystals (raphides),fragrances etc.

(1.3) BASICS IN CLASSIFICATION :-
Classification is ordering of organisms into groups. It has following three fundamental elements.
(a) Nomenclature :-(L. nomen-name calarae-call) is giving distinct names to organisms so that they can be easily recognized and differentiated from others. There are universal rules and practices, which every taxonomist has to follow. Each organism is given a scientific name with two parts-Genus and Species.
(b) Classification: - is arranging organism into categories according to systematic plan. The categories are Kingdom, Phylum (in animals)/ Division (in plants), Class, Order, Family, Genus, Species. Each category is a unit called ‘Taxon’.
(c) Identification :-It is finding of correct name and place of an organism in a system of classification. It helps in determining the similarity of an organism with an already known organism.

(1.4) NOMENCLATURE:- It is the science of providing distinct and proper names to organisms so that they can be easily recognized and differentiated from others.
Types: - It is of two types- (a) common / vernacular names –These are the names given to an organism in a particular language and region of the world like names in English, Hindi, Marathi, Gujarati, Bengali etc.e.g. Plant Gurhal (Hindi) is China Rose (in English), Padma charini (in Sanskrit), Jaba (in Bengali), Mandara (in Oriya) and Jaswand (in Marathi).

Advantages of common names: -
(i) Easy to learn, speak and write.
(ii) Are in local languages
(iii) are very short
(iv) are familiar since childhood.

Drawbacks: - (i) These names vary in different countries and different languages which creates confusion in identifying an organism.
(ii) Only animals and plants which are commonly found have been named. Small and insignificant organisms don’t have common names.
(iii) They don’t have any scientific basis and are based on superficial characters like colour (e.g. Black Bird), habit (e.g. Flying Fish), habitat (e.g. Water Lily), use (e.g. Pearl Oyster) etc.
(iv) Some names are misleading. e.g.Jelly Fish, Star Fish, , silvher fish but none of them is true fish.
(v) Certain common names have no significance.E.g. Widow’s Tears (Tradescantia), Love in mist (Nigella damascena)

(b) Scientific Names: - Given by Linnaeus (1751) in his book Philosophica Botanica. Names given by Linnaeus in 10th edition of his book Systema Naturae (published in 1758) were recognized internationally.

System of Scientific Names: -
(i) Polynomial Nomenclature: - Before 1750, names were given by adding many descript-ive words. So these were lengthy and difficult to remember.e.g.Caryophyllum saxatilis folis gramineus umbellatis corymbis was the name of Caryophyllym growing on rocks with grass like leaves and umbellate corymb arrangement of flowers.
(ii) Binomial Nomenclature: -C.Linnaeus, in 1753, proposed Binomial System of Nomenclature in his book Species Plantarum. It was a better alternative to cumbersome polynomial nomenclature. So, it was accepted. According to this system, every organism has two names- first is Genus / Generic name and second is Species name.e.g.Mangifera indica is the scientific name of Mango. Mangifera represents Genus and indica is species.
(iii) Trinomial Nomenclature: -According to this system, certain organisms have three names. First is Genus, second is Species and third is Sub-species (in animals) / variety (in plants). E.g. Homo sapiens sapiens (man, in general), Homo sapiens europeus (man of European race). Codes of Nomenclature: - There are three main international codes of nomenclature.
(i) ICBN – International Code Of Botanical Nomenclature. In 1961
(ii) ICZN – International code of Zoological Nomenclature. In 1964.
(iii) ICBN – International Code Of Bacteriological Nomenclature.
There are ICVN (International Code of Viral Nomenclature) and ICNCP (International Code of Nomenclature for Cultivated Plants) also. The codes are established and improved upon at International Botanical and Zoological Congress from time to time.
Advantages of Codes: - (i) Help in avoiding errors, duplication and confusion in scientific names.

Rules of Nomenclature: -The codes of Nomenclature set rules and guidelines according to which scientific names are given to an organism. The rules are-
(i) A scientific name has generally two words. First one denotes Genus & second Species.
(ii) Scientific name should be in Latin language only.
(iii) Names are either printed in italics or underlined separately. e.g. Homo sapiens or Homo sapiens .
(iv) Generic name always starts with capital letter and species name with small letter.
(v) Generic name can be abbreviated by using its first initial. E.g. H. sapiens.
(vi) The name of author is written in abbreviated form after species name. It is written in Roman language. E.g. Mangifera indica Linn. Linn. is for Linnaeus.
(vii) The date of species name published can also be added to the scientific name. Homo sapiens Linn. 1758.
(viii) Each taxonomic group can have only one correct name.
(ix) The name should be short, precise and easy to pronounce.

(1.5) TAXONOMIC HIERARCHY :-    It is an arrangement by which taxonomic groups are arranged in definite order from higher to lower categories. This system was first proposed by Linnaeus, so it is also called as ‘Linnaean Hierarchy’. Nearer the categories in a hierarchy, the greater is the affinity between their individuals. In all categories, only species have real existence & rest are man made. There are seven major categories of classification. Their descending sequence for animals and plants with specific suffixes or endings is as given below.

Kingdom                                                      :
Phylum (in animals) / Division (in plants) :    -phyta , -phytina
Class                                                            :    -ae     , -opsida
Order                                                           :    -ales
Family                                                          :    -aceae
Genus                                                          :
Species                                                        :

Kingdom is the highest category and Species is the lowest. The placement of an organism in sps., genus, phyla etc.is determined by similarities in their characters and relationships.

The categories in hierarchy are therefore in ascending order as shown in diagram below: -
Category: - It is a rank / level in a hierarchical classification of organism. There are seven categories.
(i) Species :-It is the basic unit of classification. It is the group of individuals with similar morphological characters which interbreed among themselves and produce their own kind. There can be many sps. belonging to same genus. E.g. Tiger- Panthera tigris, Panthera leo. But individuals of two different species cannot interbreed.
(ii) Genus: - It is a group of species, which are similar in broader features but differ in detail. E.g. Lion, tiger, Leopard, Jaguar have several common features and belong to one Genus- Panthera. Panthera leo (lion), P.tigris (tiger), P.pardus (leopard), P.onca (Jaguar). A genus can have single species (Monotypic) or many species (Polytypic).
(iii) Family: - A family is a group of related genra. e.g. Genus Felis of cats and genus Panthera of Lion, Tiger, Leopard are placed in family Felidae as they have similar characters of retractile claws.
(iv) Order: - It is a group of related families. E.g. Family Felidae of cats and Family Canidae of dogs are placed in same order Carnivora as these all have large canines & are Flesh eaters. Family Solanaceae and Convolvulaceae in plants are put in one order Polemonial because of some same floral characters.
(v) Class: - is a group of related orders. E.g. order Rodentia (of rats), Lagomorpha (of Rabbits) and Carnivora (of cats and dogs) all have hair, milk glands and are placed in same class Mammalia.
(vi) Phyla / Divisions: -A group of related animal classes is called ‘Phylum’ whereas a group of related plant classes is called as ‘Division’.e.g. In animals, Phylum Chordata includes classes Amphibia, Pisces, Reptilia, Aves and mammals since all these classes have common characters like presence of notochord, dorsal hollow nervous system & Pharynx with perforated gill slits.
(vii) Kingdom :-It is a group of phyla / divisions with certain common characteristics. e.g. all phyla of animals lack cell wall and chlorophyll. So these are placed in kingdom Animalia. All divisions of plants have cell wall and chlorophyll, so these are kept in Kingdom Plantae. Intermediate Categories: -There are smaller sub-categories also which can be added to explain finer distinctions wherever necessary. These sub-categories are sub-species (below species), sub-genra (below Genus), sub-family (below Family), Sub-order (below order), sub-class (between order and class), Sub-phylum (below phylum), sub-kingdom (Between phylum and kingdom). All these are called Intermediate Categories.

(1.6) SYSTEMS OF BIOLOGICAL CLASSIFICATION :-
There are three major systems of Biological classification.

(1) Artificial System: -This is based upon few superficial resemblances in organism rather than natural or evolutionary relationships. It was introduced by Pliny, the elder (28-79AD). Aristotle (384-322BC) classified organism on the basis of habitat. E.g. Aquatic group (animals living in water), terrestrial (animals living on land) and Aerial (in air). E.g. two groups of animals –one, which can fly, and others, which cannot fly. Theophrastus followed him and classified plants as trees, shrubs and herbs on the basis of habit. Linnaeus also followed artificial system and classified plants on the basis of number, union, and length etc. of stamens.e.g.Monandria (1 stamen), Diandria (2 stamens), Triandria (3 stamens) and Polyandria (many stamens). Drawbacks: -(i) lacks natural relationship among organism.
(ii) Leads to grouping of unrelated organisms like birds, bats, insects in flying animals.
(iii) Related organisms get separated e.g. whales in aquatic animals and rats in terrestrial.
(iv) Habits of certain animals change as they grow. E.g. Tadpoles are aquatic but when they grow as frog, they become amphibious.
(v) It does not reflect evolution of organisms.

(2) Natural System: - It was first proposed by John Ray (1627-1705) on basis of similarities and dissimilarities in plants and animals. A comparable study of number of characters is done in this system. It considers characters, which are relatively constant like morphological, cytological, anatomical characters.
The latest natural system of classification of seed plants was proposed by George Bentham (1800-1884) and Joseph Dalton Hooker (1862-1883). Advantages: - (i) brings out natural relationship among organisms.
(ii) Only related organisms are placed in a group.
(iii) Unrelated organisms remain separate.
(iv) It shows evolutionary relationship.

(3) Phylogenetic system: -This system is based on evolutionary sequence as well as genetic relationship among organisms.e.g Hutchinson system, Engler and Prantl’s system. Etc. In this system, Organisms belonging to same taxa have a common ancestor & may be represented in form of a family tree-Cladogram.
Adolf Engler and Karl A.E.Prantl (German) published their system in ‘Die naturlichen Pflanzenfamilien’ (1887-1899). According to them, flowers with only stamens or carpels formed the lowest grade of organization. They considered monocots to be primitive than dicots. Families were arranged according to increasing complexity of flower. Primitive forms have naked flowers and were kept in the beginning. The more advanced families have distinct perianth while highly evolved families have fused perianth.
John Hutchinson (English Botanist) gave his phylogenetic classification in his book “Families of Flowering Plants” in 1959.According to him-
-Trees and shrubs are considered to be more primitive than herbs.
-Dicots are more primitive than monocots.
-Polypetaly, Actinomorphic and Solitary flowers are considered more primitive than Gamopetaly, Zygomorphy and inflorescence respectively.

(1.7) CLASSIFICATION OF ORGANISMS: -

(1) Two Kingdom Classification: - It is the oldest system given by C.Linnaeus in1758.
He divided living world into two kingdoms:
(a) Plantae- includes plants. Are immobile, have autotrophic nutrition and rigid cell walls.
(b) Animalia – includes animals. Are mobile, depend on plants or other organisms for food and have no cell wall. Shortcomings of two kingdom system: -
(i) Higher organisms can be easily differentiated as plants and animals but lower organisms possess characters of both .So, it is difficult to place them in plants or animals.
E.g. Euglena has autotrophic nutrition and chlorophyll. So, it resembles plants but it lacks cell wall and is mobile. So, it is like animals also.
E.g. Sponges are immobile and branched like plants but they respond to stimuli, are holozoic and excrete nitrogenous waste material like animals.
(ii) Fungi, Bread moulds, Mushrooms were placed in plants but these lack chlorophyll and do not synthesize their own food.
(iii) Bacteria are included in plant kingdom but these lack well organized nucleus and are called prokaryotes in contrast to Eukaryotes, which have well defined nucleus.
(iv) Viruses and Lichens have peculiar characters like viruses lack protoplasm and exhibit characters of living organism inside living cell. They don’t resemble plants but are kept in plant kingdom. Lichens have association of Algae and Fungi. So, these are neither plants nor animals.
This system was inadequate. So, it was not fully accepted.

(2) Three Kingdom Classification: - given by E.H. Haeckel. According to him, the three kingdoms are

Protista included all unicellular microorganisms, which are either plants or animals. e.g. Bacteria, Algae ,Fungi and Protozoa were included in Protista.

(3) Four Kingdom Classification: -By Copeland. According to him

He placed Bacteria, Cyanobacteria in kingdom Monera.
(3) Five Kingdom Classification: Given by Robert H. Whittaker in 1969. According to him five kingdoms are,

Basis of Classification: -
It is based on four factors.
(i) Complexity of cell structure. (Prokaryotic or Eukaryotic)
(ii) Complexity of organism’s body. (Unicellular or multicellular).
(iii) Mode of Nutrition (Autotrophic or Heterotrophic).
(iv) Phylogenetic relationship.
Complexity increased during evolution. Cells became prokaryotic to eukaryotic.
Organisms became unicellular to multicellular. Mode of nutrition changed in multicellular kingdoms (Plantae, Fungi, Animalia). Plantae became Producers, Fungi were Decomposers and Animalia became Consumers.

Kingdom Monera   (The Prokaryotes): - It includes single celled prokaryotic organisms like Bacteria, filamentous Bacteria (Archaebacteria) and Cyanobacteria (Blue Green Algae). They are most primitive with following characters: -
- Are microscopic, found in deep ocean floor, hot deserts., hot springs and inside other Organisms.
-Are either unicellular or occur in colonies.
-Cells are prokaryotic with rigid cell walls.
-Nucleus and other organelles lack membranes.
-Nutrition is of different types. Most are heterotrophs, some Bacteria are autotrophs.
-Reproduce mainly by Binary Fission. Sexual reproduction is absent.
-Can survive in extreme environmental conditions like high salt concentration, high temp    erature, acidic / alkaline ph.can also survive in anaerobic conditions.

Kingdom Protista (the unicellular Eukaryotes) :-It includes unicellular and multicellular forms found in aquatic habitats. They have following characters: -
- Generally lack cell wall. If present, it is made up of cellulose.
-Have membrane bound cell organelles like nucleus, mitochondria, and E.R. and Golgi   bodies.
-May have cilia or flagella for their movement.
-Show all modes of nutrition. Protistan algae are photosynthetic autotrophs. Unicellular Free-floating algae are called Phytoplanktons. Slime Moulds are decomposers.
-Reproduce by sexual and asexual reproduction.

Kingdom Fungi (multicellular Eukaryotes- Decomposers):- They have following characters: -
-It is made up of thread like interwoven structures called ‘Hyphae’. Network of hyphae is called as ‘Mycelium’.
-Are single celled as well as multicellular
-Cell wall is made up of chitin-a nitrogen containing carbohydrate.
-Are heterotrophs having either saprophytic or parasitic mode of nutrition. Some have
Symbiotic association with algae or cyanobacteria (lichens) or roots of plants (Mycorrhiza).
-Store reserve food as oil or Glycogen.
-Hypha can undergo fragmentation & each fragment grows into new mycelium.
-Reproduce asexually by spores like zoospores, Gonidia, Conidia, Ascospores and Basidiospores. Sexual reproduction occurs by fusion of similar (isogamy) or dissimilar gametes (oogamy).

Types of Fungi: - On the basis of morphology of mycelium, mode of nutrition and mode of reproduction, fungi are of following types-
(a) Myxomycetes :-occurs in damp places and are multinucleated.
-Body is thallus shaped and is called Plasmodium.
-Have pseudopodia for movement and engulfing food.
-Body survives adverse dry conditions by becoming fruit like.
-Multiply by fragmentation, asexually by zoospores, sexually by spores acting as Gametes.

(b) Phycomycetes: -Found in water or decaying leaves.
-Are multinucleated.
-Reproduce asexually by ciliated zoospores and non-ciliated aplanospores.Sexual reproduction occurs by fusion of similar (Isogamy) gametes or dissimilar gametes (oogamy) e.g. Mucor, Albugo.

(c) Ascomycetes: -are unicellular as well as multicellular
-Asexual reproduction occurs by spores formed outside sporangium. Sexual
reproduction occurs by ascospores formed within mycelium in sac like structure-Ascus.
-After fusion of gametes, meiosis occurs to produce haploid ascospores.
-Fruiting body is called Ascocarp.
-e.g. Yeast,Penicillium ,Aspergillus.

(d) Basidiomycetes: -are called ‘Club Fungi’ because of club shaped mycelium end kno       wn as Basidium.
- Have multinucleated mycelium.
-Asexual spores Basidiospores are produced outside.
-Two compatible gametes fuse to form zygote, which undergoes meiosis to produce four basidiospores.
-Fruiting body is called ‘Basidiocarp’.
-E.g. Mushroom, Smut, Rust.

Kingdom Plantae (multicellular Eukaryotes- Producers)
-Are multicellular and photosynthetic forms called Green plants, Algae etc.
-Are non-motile except few Algae.
-Have rigid cell wall of cellulose.
-Reserve food is mainly Starch.
-Algae reproduce asexually by motile and non-motile spores.
-Are called ‘Photoautotrophs’or ‘Primary Producers’as they synthesize their food by utilizing water, carbon di oxide, minerals in the presence of sunlight and chlorophyll.Some plants are total parasites (Cuscuta) or partial parasites (Viscum) also.

Kingdom Animalia :-(Multicellular Eukaryotes- Consumers)
-Comprise of animals, vertebrates and invertebrates.
-Are multicellular without cell wall.
-Lack chlorophyll, are heterotrophic with holozoic mode of nutrition. So these are also
called as ‘Metazoa’.
-Respond to external stimuli.
-Have well developed control and co-ordination mechanism.
- Reproduce sexually only. Some lower forms show asexual reproduction also.
Significance of five kingdom classification: -
(i) System is more natural as it shows gradual evolution of early organisms into plants & animals.
(ii) It is based on cellular organization and modes of nutrition, which evolved very early in living world.
(iii) Separate Kingdom Fungi is justified as it differs from plants morphologically as well as physiologically.
(iv) Unicellular Eukaryotes like Euglena were earlier included in both plants and animals. But now placing them in separate kingdom Protista has eliminated this anomaly.
This system was better than all systems and resolved many problems also. But still, it was not perfect and had certain drawbacks like
(i) Kingdom Monera and Protista are still heterogenous. Both include autotrophic and heterotrophic forms and organisms with or without cell wall.
(ii) Phylogenetic relationship of lower organisms is not fully reflected.
(iii) Slime moulds differ from other Protists with which they are combined.
(iv) Multicellular Green algae cannot be phylogenetically separated from unicellular algae and therefore unicellular algae are placed in Plantae whereas these should be in Protista.

(1.8) TAXONOMICAL AIDS :-
Definition: The aids, which help in taxonomical studies, are called Taxonomical Aids. E.g. Herbarium, Museums.
Some aids are-
(1) Herbarium: -Definition-It is a collection of pressed, dried and preserved plants on paper sheet which are properly labelled, arranged and available for reference or study.
Tools required in Herbarium: -
(i) Digger for digging roots.
(ii) Scissor for cutting twigs.
(iii) Knife for cutting woody twigs.
(iv) Pole with a hook for collecting parts of tall trees.
(v) Vasculum for keeping plant specimens.
(vi) Plant Press for pressing parts of plants.

Steps in preparation of Herbarium: -Regular field visits are done and specimens collected. Information about place, habitat, season and collection time is noted. The collected specimens are kept in a box called Vasculum to avoid loss of moisture and distortion. Specimens are spread out, dried in between folds of newspapers and pressed in Plant Press, which is a set of two boards with straps. Bigger specimens are folded in ‘n’ or ‘w’ form. Some leaves are spread to show dorsal surface and some to show ventral surface. Dried specimens are pasted on herbarium sheets of standard size (29 x 41 cms.). All pasted specimens are sprayed with fungicides like 0.1% mercuric chloride. Heavier plant parts like seed, fruits are put in a packet and attached to the sheet.

Technique of Herbarium
(i) Pressed and dried specimens are mounted on thick paper with some adhesive.
(ii) Small paper envelopes ‘Fragment Packets’ containing seeds/fruits are attached to herbarium sheet.
(iii) Sheet is labelled on right corner with following information-
Name of Institution –
Scientific name of Plant-
Common / Vernacular Name-
Family -
Locality -
Date of collection -
Collection Number-
Name of Collector-
(iv) Pesticides are sprayed on specimens to keep them pest free.
(v) Mounted, labelled and treated specimens are stored in herbarium cabinets, which are insect and dust proof.
(vi) An Index register is maintained to locate desired specimens easily.

(2) Botanical Gardens: -
Definition- It is a place where plants of various groups are grown for scientificstudy, conervation, public education, aesthetics and recreation. Major botanical Gardens-There are thousands of Botanical Gardens in the world. About 800 are listed in International Directory of Botanical Gardens published by Henderson in 1983.

In India- (i) Indian Botanical Garden, Kolkata.
(ii) National Botanical Research Institute, Lucknow.
(iii) Garden of Forest Research Institute, Dehradun.

In World- (i) New York Botanical Garden, USA. (1801)
(ii) Royal Botanical Garden, London. (1600)
(iii) Main Botanical Garden, Moscow.
(iv) Botanical Garden, Montreal, Canada.

(3) Museums: -Definition-It is a place where preserved plants and animals are kept for reference and study.
Plants like Algae, Fungi, Gymnosperms, which cannot be kept in herbaria, are kept in museums. Plant and animal specimens are fixed in chemical solution identified and are labelled to be preserved for longer duration. Museums help in taxonomic studies.

(4) Zoological Parks (Zoo/Zoological Garden): -Definition-It is an enclosed space where live wild animals are kept for public exhibition. There are over 3000 zoological parks in India.
Aim of Zoological parks: -The main purpose is to breed those animals, which are facing threat in their natural habitat. Information about common names and scientific names is also displayed.

Keys: - Definition:-A scheme for identifying plants and animals is called ‘Key’. It is based on contrasting characters. Separate keys are required for different categories like family, Genus, species.
Types: - It is of two types:
(a) Indented (Yoked)- In this, two or more statements of characters of species are given to make choices. E.g. To identify Genra in family Ranunculaceae, characters of carpels and fruit of specimen can be considered as Indented Keys. The first choice starts with carpels.
(b) Bracketed – Pair of contrasting statements are used for identification.
Animals can also be identified by using Keys. Distinguishing features are recorded for each group. Questions are framed and answers are given in yes or no.

ORIGIN AND EVOLUTION OF LIFE

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:35:00 +0000

INTRODUCTION: Living beings originated on earth. But when did this life originate and how? These questions are answered in this chapter. So, to study history of life, two events are studied: -
(i) Origin of Life
(ii) Evolution of Life

(1.1) ORIGIN OF LIFE:Life was present on earth about 3.9 billion years ago because some rocks which are 3.9 billion years old have carbonates which resulted from life processes only. The oldest rock (4.3 billion years ago) didn't show any signs of life. There are many theories on origin of life.

(1) Theory of Special Creation:Proposed by Spanish monk Father Suarez. It states that life originated on earth from some supernatural force of God in the same form as they exist today. Life was created by God in six days. 1st day- earth & Heaven. 2nd day- sky and water. 3rd day- Lands & plants. 4rth day- sun, moon, stars. 5th day- fish & birds. 6th day-man (Adam), woman (Eve) and other animals.

(2) Theory of Spontaneous generation: (Theory of Abiogenesis) –Proposed by Anaximander (611-541 B.C.) and Aristotle (384-322 B.C.). It states that life originates spontaneously from non-living matter like rain, mud, air, dung etc. But Louis Pasteur (1862) proved that new microorganisms arise from pre-existing microorganisms.This rejects Abiogenesis theory and states that new life arises from pre existing life only.

(3) Cosmozoic Theory : ( Interplanetary Theory/ Theory of Panspermia): Given by Richter(1865) and Helmholtz(1884). Supported by Arrhenius (1908). It states that life originated in the universe and reached the earth from some other heavenly body in the form of seeds (sperms) or spores in meteorites or spaceships. On earth, these found fertile soil and grew into organisms.But this theory is not accepted because when spores travel from universe to earth, these cannot survive extreme conditions of interplanetary space like extreme cold, dryness, intense cosmic and u.v. radiations.

(4) Modern Theory/ Naturalistic Theory/Theory of Chemical origin/ Terrestrial origin
Chemosynthetic Theory :Formulated by Haeckel. Supported by Oparin (1923) and Haldane (1928). Most favoured theory. It states that life originated from inorganic substances through series of reactions. Organic molecules collected and formed life. This means chemical evolution precedes biological evolution and this process involves following events: -
(a) Origin of Earth: -To study origin of life, origin of earth must be known. According to Big-Bang theory, there was a big thermonuclear explosion of a dense entity about 15 billion years ago. Universe originated from that. About 4.5 billion years ago, solar system was formed from gaseous cloud Solar Nebula. Nebula kept on collapsing till it became flat disc of atoms and particles. Its central part became very hot & formed sun. Atoms and dust moving around the center collected to form clumps. Clumps further aggregated with other particles, grew in size and became planets. Earth had solid part-Lithosphere and gaseous part- Atmosphere. Liquid part-Hydrosphere was formed when earth cooled to temperature below 100 degrees centigrade.
(b) Chemical origin of life: -Given by Oparin (1923) and Haldane (1928). It states that organic molecules and life were formed from simple compounds through series of chemical reactions in ocean about 4200 million years ago. This theory could be tested and explained, so it was the widely accepted theory. Successive steps of chemical origin of life are:
(i) Formation of early molecules: -
-First living things evolved from non-living things.
-Spontaneous generation of life under present environmental conditions i.e. oxidizing
is not possible. So, at that time environmental conditions at that time were reducing type (without free oxygen) and not oxidizing type.
-In primitive atmosphere, oxygen was not present in free gaseous form (O2) but occurred as bound in water or as oxides of metal (pyrites, uranites etc.)
-The early atmosphere was rich in hydrogen occurring as CH4, NH3 and H2O.
-Atmospheric water vapour condensed into water drops and fell as rain. It rolled down on surfaces of rocks, accumulated at a place and formed pools and oceans. During this, minerals washed from rock surfaces into pools and oceans and dissolved in it.
(ii) Formation of simple organic molecules: -
-- Solar radiations, heat radiations from lightening, heat from volcanic activities, cosmic rays provided energy for chemical reactions.
-- Accumulated water was termed as “Hot Dilute Soup” (Haldane) / Warm Little Pond (Darwin)/ primordial soup (Oparin). It was hot, alkaline (pH=8) and rich in amino acids fats, sugar, and nitrogenous bases. It acted as stage for combination of chemical elements and setting of chemical reactions.
-- Amino acids, fats, sugar and nitrogenous bases combined to form proteins, nucleic acids polysaccharides etc.

Evidence in support of Oparin-Haldane Theory-
--Miller and Urey Experiment- Harrold C. Urey (1893-1981) and his student Stanley Miller (1953) successfully experimented Oparin-Haldane theory. They simulated it. Miller put H₂O, CH₄, NH₃ and H₂ in a spark chamber. For source of energy- they used two ele-ctrodes to provide electrical energy. For evaporation- He connected the spark chamber to another flask with arrangement for boiling water. For rain and Haldane's soup-He connected the other end of spark chamber to a trap by a tube that passed through condenser .The trap was then connected with a flask for boiling water to provide circulation.
'Control'- Control experiment was set up which contained everything except energy source.
Results- After 18 days, good amount of organic compounds like amino acids, other monomers appeared in the aqueous sample whereas in Control apparatus insignificant amount of organic compounds were seen.

(iii) Formation of complex organic molecules (Polymerization): -
The small and simpler molecules combined to form larger and complex molecules. e.g.
Simple sugars formed complex sugars (starch), amino acids formed Proteins, fatty acids and Glycerol formed   Fats.
--These chemicals occurred in 'hot dilute soup' or 'broth'.
--For polymerization to go on, two requirements should be met
a) Adequate source of energy (must have been provided from sun, lightening, ATP)
b) Removal of water from surface of reactants so that they can concentrate and polymerise further. It also might have been provided by evaporation from solar heat.

(iv) Formation and interaction of macromolecules: -
Miller's experiment suggests that prebiotic molecules must have formed under the
conditions present at that time. But formation of molecules doesn't mean origin of life.
--Three conditions should be fulfilled for origin of life
a) Continuous supply of self producing molecules.
b) Replicators should mutate.
c) Supply of free energy and partial isolation from general environment is must.
--T.Cech and Atman proposed RNA as first macromolecule as it can act as a substrate & an enzyme.
--S.Fox (1957) suggested Protenoid (formed from heating of amino acids) as first macro-molecule.

(v) First cell like structures/ Protocells: -
These self-replicating molecules are called Protobionts/Ebionts.
--These showed mutations because of high temperature in early earth atmosphere.
--Two main Protobionts are Coacervates and Micro spheres.
--Coacervates are the colloidal aggregates formed by chemicals under proper temperature 'pH and ionization. Oparin (1924) observed that when a mixture of large protein and a polysaccharide is shaken, coacervates are formed. Their interior has protein, polysaccharide and water. It is separated from outer aqueous solution, which has very less Protein and polysaccharide. But these coacervates don't have lipid membrane and cannot reproduce. So these cannot be considered as precursors of life.
--When artificially produced organic compounds are mixed with cool water, micro spheres are formed. If mixture has lipids, then micro spheres formed have lipid membrane. Sydney Fox (1950) heated mixture of dry amino acids between 130-180 degrees centigrade and then cooled it in water. Protenoid micro spheres were formed (1-2 micron meter in diameter). These can form new Protenoid by budding induced artificially. But again, these have limited diversity so cannot be wholly regarded as precursors of life.
--First cell like structures were self-duplicating nucleic acids, water and other organic or inorganic molecules.
--Protobionts had chromophores (molecules that absorbed light), which made them energy transducing devices.
--Early life (Protolife) was mainly driven by solar energy.
--Proteins acted as enzymes to form DNA genes.
--First cells used RNA as genetic material.
--DNA evolved from RNA template.

(vi) First Living Beings: -
--First cell acquires reproducing characters and becomes first living being.
--First living beings had naked DNA and RNA as genetic material.
--The earliest living organisms were Anaerobes, which depended upon existing organic molecules for their nutrition. So these were Heterotrophs.
--As gradually, supply of organic molecules diminished, heterotrophs would have changed into autotrophs.

(vii) Development of Chemoautotrophs: -
--Heterotrophs consumed food (chemical compounds). This resulted in formation of org-anisms, which synthesized their own food. They obtained energy for food synthesis from degradation of organic compounds. Such organisms were called Chemoautotrophs.
--Chemoautotrophs synthesized their own food by process called-Chemo synthesis.
--E.g. of Chemoautotrophs are Bacteria, Sulphur Bacteria.

(viii) Development of Photoautotrophs: -
--Organisms developed Chloroplasts, which absorbed light energy.
--These then performed Photosynthesis and made their own food. So, these were called as    Photoautotrophs.
--Photosynthesis released oxygen. So, the atmosphere became oxidizing type from reducing type.
--This change in atmosphere initiated evolution of life towards diversities.

(1.2) EVOLUTION :-
term 'Evolution' was first given by Herbert Spencer. It is a process of slow and gradual change. But observers tell that diverse forms have common characters pointing to common ancestory. E.g. Mammals & Amphibians have limbs for locomotion, birds have wings for flying, and Fish have fins for swimming.
According to Darwin, Evolution is Descent with modification. It may be 'Progressive' (Simpler to complex forms) or 'Retrogressive' (complex to simpler forms).

(1.3) IDEAS ON EVOLUTION: -
(i) Ancient Indian Thought: -Ancient Indians studied Evolution. Thoughts about Evolution are given in Manu Samhita/ Manu Smriti (200 A.D.). Ayurveda deals with origin of life.
(ii) Ancient Greek Thoughts: -First theories of Evolution came about 2000 years before Darwin.
--According to Plato (428-348 BC), God is perfect and everything on earth are His ideas. Each species was an unchanging ideal form (eidos).
--Aristotle (384-322 BC) put Plato's concept in a chain like series of form. He called it 'Scala Naturae' or 'Ladder of Nature'. This series was from imperfect to perfect species.

(1.4) EVIDENCES OF EVOLUTION:-
There are strong evidences of organic evolution due to which it is accepted. The evidences are obtained from studying different aspects of life of plants and animals.

(a) Biogeographical evidences: - Biogeography is the study of distribution of species. Some species are restricted to a particular geographical area and are found nowhere else. These are called 'Endemic'. Some species are found everywhere and are called 'Cosmopolitan'.

--Darwin studied evolution during his sea voyage in Galapagos Islands (group of 22 different islands, lies on equator, are 900 km. off west coast of south America). He observed unusual plants, insects, lizards, and giant tortoises, meter long Iguanas and seashells. There were no woodpeckers and insect eating warblers. But variety of Finches were present which were originally seed eating but became insect eating on island. These were different type of Finches with different type of beaks but all originated from a common ancestral seed eating stock of Finches. They radiated to different geographical areas, underwent adaptations in beaks and emerged as new species. This is called 'Adaptive Radiation'.

--Darwin studied marsupials in Australia. Some marsupials resemble other placental animals living in other continents, which have similar habitat as Australia. Natural Selection favoured those changes, which made these two groups alike. This is called 'Parallel' or 'Convergent' Evolution.

(b) Anatomical evidences: - The similarities in anatomical structure prove descent from a common ancestor.
(i) Homologous Organs: - are the organs having common origin but performing differentfunctions. Term 'Homologous organs' was given by Richard Owen (1804-1892).
E.g. Forelimbs of bat, humans, whales, birds have same structural plan.
E.g. Thorns of Bougainvillea and tendrils of Cucurbita are located in same axillary position. E.g. Brain in different vertebrates has homologous structure. E.g. Heart in all groups have same basic plan but it has been criticized also saying that heart has undergone evolution from mammals to fishes. Fish heart has two chambers (1 auricle, 1 ventricle).
When fish changed to amphibians (on land), mode of respiration also changed. Separation of oxygenated and deoxygenated blood became necessary. So heart became three chambered (2 auricles, 1 ventricle). Amphibians changed to reptiles, which have heart with two auricles and an incompletely divided ventricle. In birds and mammals, ventricle became completely divided and heart became four chambered.

(ii) Analogous Organs: - Organs with similar function but different structure and origin.
E.g.-Wings of birds and wings of butterfly, Eyes of octopus and eyes of mammals, Flippers of Penguin and Dolphin, Tuberous root of sweet Potato and underground stem of Potato.

(iii) Vestigial Organs: - Organs, which are, present in rudimentary form in the body but do not perform any function. Adaptations of organisms to new environment made these structures useless. E.g. Vermiform appendix in humans, Ear pinna, Jaw apparatus in reptiles, Nictitating membrane of eye, Wisdom tooth.

(c) Embryological evidences: - These indicate that embryos of all vertebrates have similarity. They have many features, which are absent in adults. Similarities are-
(i) Similar early development- development in all starts from Zygote →Morula→ Blastula→ Gastrula → Adults.

(ii) Resemblance in Embryo- Early embryos of all vertebrates resemble in shape and str-ucture. They have same head with eye/ear rudiments, visceral arches, embryonic tail etc. Embryos of closely related vertebrates resemble more. This shows that all vertebrates have evolved from a common ancestor.

(iii) Recapitulation Theory –von Baer (1826) gave von Baer's Law. Later, Ernst Haeckel called it as Biogenetic law (1866). This law states that Ontogeny (the ancestral sequence) is recapitulation/repetition of Phylogeny. Von Baer disapproved the Biogenetic law. He noted that embryos never pass through ad-ult stages of other animals. But recapitulation has importance.E.g. Seedlings of Acacia tree first develop simple leaves, which later change into compound leaves.E.g. Modern day Oaks of southern U.S.keep their foliage throughout year but Oaks of northern U.S. shed their leaves in winter.

(d) Palaentological evidences: - Paleontology is the study of fossils. Fossils are the pres-erved remains of the organisms that lived in the past. Organism or body part of organism gets preserved when it buries under mud or rocks where decay doesn't take place. Foot-prints, skeletal remains, organic molecules serve as fossils. Age of fossil can be found out by finding age of the rock where it is present. Rocks in deeper strata are older than rocks in upper strata. Amber is best material for fossilization. Absolute Dating is the method in which rocks are dated by measuring the degree of decay of radioactive isotopes, which were inside the rock when it was formed. By Dating, Geological Time Scale was prepared. It has five eras, which are subdivided into periods that refer to stages of evolution of life. When we arrange fossils (from older to younger), we get evidences for successive changes in organism. First, there were Fish fossils, then amphibians, then reptiles, next mammals and birds. All major group of vertebrates are linked. Sometimes older fossils are linked to modern species by transitional forms. Vascular plants have left very few fossils, which have gaps also. There are few lineages also that appear to arise suddenly in fossil records and stayed as such for hundreds of million of years like sporangia (contain spores) are present at tip of the plant in primitive Psilopsida. These are placed at the base of leaf in modern Lycopsida. These are arranged on whorls on top of plant in Sphinopsida
This arrangement has been there for more than 350 million years.

A Lineage is evolutionary sequence arranged in linear order from ancestral group to descendent group. The continuous change of characters within an evolving lineage is 'Ev-olutionary Trend'. The number of trends in any lineage = number of characters evolving.
A trend can be 'Progressive' (increase in organ size) or 'Retrogressive' (decrease or degeneration of organ). E.g. Evolution of horse reveals number of trends. Evolutionary trend among horses was not universal. Direction and speed of evolution are subject to variation. Major evolutionary trend of horses are-
-Increase in size, loss of toes, lengthening of toes, lengthening of limbs, increase in height, brain enlargement, change in Dental pattern.

(e) Morphological Evidences: -There is similarity in external structure of organisms, which shows a common ancestory. E.g. In plants, there is structural similarity in having roots, stem, leaves, flowers etc.

(1.5) THEORIES OF EVOLUTION: -
Many evidences have proved that evolution occurs but how does it occur or what is the mechanism of evolution has been explained by four main theories.

(1) Lamarckism:-Put forth by French Biologist Lamarck (1744-1829). He published it in his book'Philosophique Zoologique'in 1809. Lamarck arranged fossils in chronological order (from older to younger form) and he could see various lineages also. According to his theory-
(i)Living organisms and their body parts continually increase in size.

(ii) New organs develop due to new needs and are maintained too.

(iii) Continuous use of an organ leads to its development and disuse causes its reduction.

(iv) Acquired characters due to use and disuse of an organ are passed to the offsprings.

Explanation of theory: - This theory was explained by certain examples like-
(i) Giraffe: - Earlier, giraffe used to feed on ground but when grass fell and lower foliage disappeared, they had to stretch their neck and eat upper foliage. This resulted in their long neck, which was passed on to next generation.

(ii) Aquatic birds: - these have arisen from terrestrial ancestors. They had to go into water for food and protection. For that, they stretched their skin and spread their toes. Gradually web developed between toes.

(iii) Deer: - Speed of deer is due to continuous running for protecting itself from enemies.
Criticism of theory: - Lamarck's theory was successful in explaining evolution but it proved faulty later and was not accepted fully.
--First proposition of increase in size was not correct. Evolution shows reduction in size.
E.g. Trees are primitive and herbs/shrubs have evolved from trees.
--Second proposition is also false. E.g. wings cannot be developed if we wish to fly.
--Third proposition has truth and is correct. This can be explained by examples of Giraffe, Deer, Aquatic birds given above.
--Fourth proposition of inheritance of acquired characters is not correct. But there are evidences against it and favour of it.
Evidences against it were given by German Biologist August Weismann (1834-1914). He put forth his theory of continuity of Germplasm. He said that each animal has 'Germ Cells' and 'Somatic cells'. Any change in somatic cells is not heritable whereas changes in Germ cells are passed on to next generation. Use and disuse of organs effects Somatic cells only, which means acquired characters, reside in somatic cells. Thus these are not inheritable. He gave some examples also. e.g. In rats, he cut their tail for 80 generations but tailless rats were never born. E.g. Women have been piercing their external pinna for thousands of years but it has never been inherited.
Evidences in favour of it go against of Weismann's theory and show that acquired characters are inherited to some extent through somatic cells also. Packard, Spencer, Mcdougall removed objections against Lamarckism. This revived the discarded Lamarckism and modified 'Neo-Lamarckism' was formed. E.g. Mcdougall trained rats to escape routes. It was found that number of errors made by rats decreased generation after generation.
Conclusion: - There are more evidences against than in favour of Lamarckism. So, this theory was not accepted.

(2) Darwinism: - Charles Robert Darwin (1809-1882) gave this theory. He went on voyage for five years, came back and published a book 'Origin of Species' (1859). Idea of natural selection struck his mind after examining Malthus work who wrote 'Principles of Population' stating that food supply increases in arithmetical progression and population increases in geometrical progression.
The main postulates of Darwin are: -

(i) Rapid Multiplication: - Each species produces offsprings in large numbers, multiplying in geometrical progression i.e. doubles in Ist year, increases to four times in 2nd year, eight times in 3rd year and so on. E.g. Paramecium divides three times in 48 hrs, Plants produce thousands of seeds each year.

(ii) Limited food and Space: -Because there is limited food and space; the population of a particular species remains constant.

(iii) Struggle for existence: -As there is limited food and space, offsprings compete severely for requirements. This is called 'Struggle for Existence'. It can be'Intraspecific' (Between individuals of same species. It is toughest as requirements are similar.) Or 'Interspecific' (between different species). “Environmental struggle' is the struggle with changes in environment.

(iv) Variations: - Struggle for existence among organisms changes them according to the conditions. These changes are called 'Variations'. Variations, which are most suited to the organism, are transmitted to next generation while unsuited variations are eliminated.

(v) Survival of fittest: -The organisms, which adapt to changes, survive.e.g. In drought,
Only those plants will survive which can maximize absorption of water. The competition is so severe that only few out of millions survive.

(vi) Inheritance of useful variations: - The individuals, which get selected by nature in struggle for existence, pass these variations to next generation.

(vii) Formation of new species: -New species arise by gradual modification of older ones. In each generation, new favourable variations appear and complement the already inherited variations. After number of generations, there are so many variations in an indi-vidual that it becomes a new species.

Criticism of Darwin's theory: - Darwin's theory is the most recognized theory today but it has evidences going in favour of it and against it.
Evidences in favour:
-Excessive multiplication, limited food and space, struggle for existence, variations, natu-ral selection can be easily seen in nature.
- Artificial Selection, which is done by man in breeding experiment, shows support for
Natural selection done by nature. In Breeding experiments, man also selects individuals
with desired traits and allows them to mate for creating a new breed of animals. If man
can do so with limited resources, then nature can easily produce new species with its vast resources.
-Position of nectars in flowers is related to proboscis of insects, which pollinate them. This cannot develop suddenly but evolved gradually by natural selection.

Evidences against: -
-According to Darwin, evolution starts with small variations i.e. organs appear as small structures first and then grow. But in case of organs like wings of birds, If they were small initially then they were useless. Then how could these be passed to next generation when these were not advantageous?
-Vestigial organs have no function, then why these exist generation after generation
-Tusks of elephant, antlers of deer have overdeveloped causing hindrance, then why these were selected.
- According to Darwin, process of evolution is linked with inheritance. But he could not explain the basis of variations and how these variations are passed to next generation. In 1868, he gave Theory of Pangenesis according to which every organ produces minute particles'Pangenes'which are carried by blood and collect in the gametes. But Weismann's Germplasm theory (1892) states that germ cells separate from somatic cells early in development. So changes in somatic cells cannot be inherited. This disapproves Darwin's theory.

(3) DeVries Mutation Theory :-Put forth by Hugo deVries in1901. Darwin couldn't explain origin of variations. Hugo deVries proposed Mutation Theory to explain it. His observations were on wild variety of Evening Primrose (Oenothera lamarckiana). He states that new species arise from preexisting ones suddenly because of 'mutations', which are discontinuous and inheritable variations. So, this is discontinuous and sudden process instead of continuous and gradual as told by Lamarck and Darwin. DeVries said mutations are raw materials for evolution. Natural selection selects useful mutations and eliminates harmful ones.
Features of deVries Theory: -
-New species originate as a result of discontinuous variations that appear suddenly i.e. mutations are raw material for evolution.
-Same mutations can appear in several individuals of a species.
-Mutations reoccur. Same mutations appear again and again and increase their chances of selection.
-Mutations can occur in all directions.
-Nature selects beneficial mutations and eliminates useless mutations.
-Evolution is discontinuous and jerky process.

Criticism: -This theory has also, evidences in favour and against it.
Evidences in favour: -
(i) MacDougal and Shull repeated deVries experiment & obtained same results.
(ii) Mutations occur in same way as told by deVries.e.g. Short-legged Ancon sheep appeared from ordinary sheep all of a sudden in 1891. It was beneficial to farmers, as it could not jump over fences. E.g. Hornless cattle were produced all of a sudden in 1889.
(iii) Oenothera lamarckiana has 14 chromosomes but its mutant varieties have 16, 20, 22,24,28,30 chromosomes. This shows that mutants are independent species.
(iv) Mutations are inheritable.
Evidences against: -
(i) Mutations occur rarely, so how could variety of animals and plants appear by variations.
(ii) Mimicry, Camouflage, relationship of nectar position with insect proboscis cannot appear suddenly.
(iii) Mutations are recessive but evolution occurs due to inheritance of dominant mutations.

Significance: - deVries Theory was accepted. Mutations were found to be inheritable. But Evolution cannot occur just because of mutations. There are other factors also.

(1.6) MODERN CONCEPT OF EVOLUTION: -Modern concept of evolution is modification and elaboration of Darwin Theory. So, it is also called as 'Neo-Darwinism'.
There are changes and diversification (evolution) of organism through geological time.
This is called 'Macroevolution'. It results in changes (evolution) in hereditary material i.e. at genetic level and this is called as 'Microevolution'. Modern view says that populations are units of evolution and natural selection is the mechanism of evolution.
Population Genetics: - Population is the group of individuals belonging to the same species in the same area at a particular time. Study of frequency of genes in a population is known as 'Population Genetics'. When relative frequencies of different DNA in a population change over time, evolution takes place.G.H.Hardy and W.Weinberg (1908) gave Hardy-Weinberg equilibrium/principle, which was a simple mathematical relationship to study gene frequencies. It is:
dominant genotype.

p + q = 1
(p + q)² = p² + q² + 2pq
where
p² = frequency of dominant genotype
p = dominant gene
q² = frequency of recessive genotype
q = recessive gene
2pq = frequency of heterozygous dominant genotype

Both scientists studied genetic structure in a population, which didn't show evolution.
They noted that under certain constant conditions, the gene frequencies also remain cons-tant in a population through generations. So, when this Hardy-Weinberg Eqbm. disturbs, Evolution takes place.

Sources of Variations :-
Individuals in a population are similar in many ways but they are different also in some ways. If a population has to evolve, then it should have variations. Variations can be at two levels:

Natural Selection acts on genetic variations. Then it expresses itself in a phenotype. So,Evolution requires genetic variation. Evolutionary agents change the genotype frequency in a population and cause deviation from Hardy-Weinberg Eqbm. There are five basic processes that affect Hardy-Weinberg Eqbm. And cause variations.

(i)Mutations: According to Hugo deVries, mutation is a random and sudden heritable change. Mutation rate is very slow but can cause considerable genetic variation.
Joshua Lederberg and Esther Lederberg (1952) performed experiment to show that there are Preadaptive mutations. Preadaptive mutations are advantageous and express themselves only when organism exposes itself to new environment according to which it has to adapt. So, these mutations already occurred but got selected later.
Experiment: They tookE.coli culture and spread it on master Agar plate. Each cell formed a new colony. They took imprints of these colonies on a velvet cloth. Then a replica plate with this velvet cloth was taken. A new plate containing Penicillin as medium was also taken and imprints from replica plate were touched on it. Certain colonies did not appear. The colonies, which appeared, were only those, which were resistant to antibiotic Penicillin. This means resistance to Penicillin (a mutation) had already occurred even before culture was exposed to Penicillin.

(ii)Recombination :It causes evolution. In meiosis, genes combine during crossing over and new combinations are produced. These new combinations occurring at different time and places recombine to form new alleles, which cause evolution.

(iii)Gene Migration: Members of a population sometimes migrate to another population. If they breed with them, new alleles are formed. This is called Gene Migration. If inter- breeding populations are closely related, fertile hybrids are produced. So, gene flow takes place when individuals enter or exit a population. This causes Evolution.

(iv)Genetic drift: is the elimination of certain genes when a section of population migrates or dies due to sudden natural calamity.
When genetic drift occurs in a population derived from small band of colonizers called 'founders', then huge changes occur and a totally different new species is formed. This is called 'Founder Effect'. Sometimes there is drastic reduction in allele frequency due to any chance event and this reduces population, which is not able to re-establish itself. Such reduction in allele frequencies is called 'Genetic Bottleneck'.

(v)Natural Selection: This is the method of differential reproduction. which means that some members of a population have genes, which enable them to grow up and reproduce faster. Thus their number of offsprings increases in next generation. If this keeps on going for many generations, then the genes of individual producing more offsprings becomes predominant in a gene pool of a population. This changes gene frequency. Only those organisms, which are best adapted to environment, have more surviving off springs. This is called 'Directional Selection' also and leads to evolution.

(1.7) GENETIC BASIS OF ADAPTATION :-
According to Darwin, Natural selection leads to evolution. Genetic variations occur in an organism. If those are favoured by natural selection, adaptation takes place. If there is no genetic variation, there is no adaptation and there will be no evolution.
Industrial Melanism (Example of Natural Selection): - Peppered MothBiston bitularia lives in England and shows cryptic colouration. There are two types of moths –Light (gray coloured) and Dark (black coloured). In the beginning, there were more light varieties but during 1850-1950, the population of dark varieties increased specially in polluted industrial areas like Birmingham. This was Evolution. Biologist's explanation to this was-
In the beginning light moths rested on pale tree trunks. Their light colour camouflaged with tree trunk colour and provided them protection from enemies. But in industrial areas
There was more pollution. Black soot deposited on tree trunks and light moths became easily visible on dark trunks. So, to protect themselves, these light moths adapted and changed to dark (melanic) moths. This evolution of darker forms in response to industrial pollution is called 'Industrial Melanism'.
Bernard Kettlewell tested it in 1950. He reared dark and light varieties of moths in equal numbers. Then he released one group in polluted area (Birmingham) and other in Unpolluted area (Dorset). The results were-

In Birmingham – 19% light moth, 40% dark moths were recaptured.
In Dorset - 12.5% light moths and 6% dark moths were recaptured.

Reverse Evolution –' Clean Air Legislation' was passed in Britain in 1956, which reduced pollution. As a result of this, melanic moths also decreased in number. This was reverse Evolution. But genes for light moths did not disappear completely.
Natural Selection and Polymorphism :-
When two or more distinct forms are present in a population then that population is called 'Polymorphic'. E.g.1- ABO blood groups in humans. There are four forms-Type A, Type B, Type AB and Type O. e.g.2- Sickle Cell genes in humans. These genes cause sickle cell anaemia, which is lethal. Normal Haemoglobin gene is HbA, which mutates and changes to defective gene HbS. HbS makes RBCs sickle shaped and unable to carry oxygen, which causes death of the organism. Homozygotes with normal alleles (HbA/HbA) or with sickle cell alleles (HbS/HbS) suffer from malaria easily. Sickle shaped RBCs of heterozygous individuals (HbA/HbS) kill malarial parasite. Thus the individual heterozygous for defective haemoglobin fights malaria better than homozygous normal individual. Because of this, natural selection has favoured the occurrence of sickle cell genes in malaria-affected regions. Homozygotes (HbS/HbS) die but heterozygotes (HbA/HbS) reproduce and balance the loss. So, this is also called 'Balancing Selection'. It occurs rarely.

(1.8) SPECIATION: - Process of formation of new species from existing ones is called Speciation. It is of two types-

(a)Allopatric- When a population splits up into two or more populations because of geographical barriers like glaciers, ocean, mountain etc. e.g. Formation of new species of Darwin's Finches in Galapagos Islands.

(b)Sympatric- Formation of new species within a population without any geographical
Isolation. New species formed is reproductively isolated from parent species. This occurs when chromosomes fail to segregate during meiosis or replicate without under-going mitosis. E.g. Polyploidy- normal chromosome number multiplies.

Isolation:- Reproductive Isolation is the mechanism which stops the population of two different species from interbreeding. It maintains integrity of species by checking hybrid-isation. Factors, which prevent interbreeding between species, are calledIsolating Mechanisms'.
These are of two types-

(i)Pre-mating Isolating Mechanisms: - These operate before mating and are of many types depending upon the isolating mechanism involved.
a) Geographical- No interbreeding because of separation by physical barriers like sea, mountain, desert etc.
b) Genetic: -No interbreeding because of sterility.
c) Ecological: - Two species live in different habitat of same geographical area Thus, they cannot interbreed.
d) Temporal: - No interbreeding because of different breeding times in different species.
e) Behavioral: -No interbreeding due to different courtship and mating behaviours.
(ii) Post mating Isolating Mechanisms: -These operate after mating and are of following types.
a) Hybrid In viability-Mating between two species occurs, fertilization may occur, hybrid
may be produced but is not viable and dies later.
b) Hybrid Sterility – Mating occurs, fertilization occurs, hybrid is produced but is sterile.
So, no further reproduction takes place.
c) Hybrid Breakdown (F2): -Mating occurs, Fertilization occurs, vigourous F1hybrids are   produced. Back Cross occurs. F2 hybrids are produced which are less fertile.
d) Incompatibility – Mating may occur but no fertilization or development takes place.

Significance of Reproductive Isolation: - It is essential for formation of new species. But hybrids can be produced in laboratory between species that do not interbreed in nature. E.g. Mule (sterile)- Male Donkey x  Mare (female horse)
E.g. Hinny (sterile)- Stallion (male horse)    x    female Donkey
E.g. Tigons (fertile)- Asian Tigers    x     African Lioness.

(1.9) SPECIES CONCEPT:-
Species is the basic unit of classification. Taxonomists have defined species in many ways. According to Davis and Heywood, species is assemblage of individuals with morphological features in common and separable from other such assemblages by corre-lated morphological discontinuities in a number of features. Lumper combines population into single species or group. Splitter separates population into different species or group. According to many biologists, there is a biological species concept according to which a species can be defined as sexually interbreeding group of individuals separated from other species by reproductive isolation. Members of same species can interbreed and produce fertile offsprings. But members of different species cannot inter-breed.
Sibling Species: - two species, which are morphologically identical but cannot interbreed, are called as sibling species. E.g.Drosophila pseudoobscura andDrosophila persimilis.

Polytypic Species: - When different species which are morphologically and geographica-lly separated are put under single group/species based upon their cross fertilization then that group/species is called Polytypic species. E.g. various species of North American sparrows are united with multiple geographical races of song sparrows. But concept of polytypic species is not valid as some organisms are asexual also.

Evolutionary species concept: -Many biologists gave this concept and defined species on the basis of evolutionary isolation and not sexual isolation. According to George Simpson(1961), an evolutionary species is a lineage evolving separately from others and
With its own evolutionary role and tendencies. In this method, many factors like genetic, Morphological, behavioral, ecological are considered but still it does not provide solution to all problems.

CLASSIFICATION OF PLANTS

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:29:00 +0000

Introduction: Plants are included in Kingdom Plantae. These were classified into major groups, each with distinct characters.

(5.1) CLASSIFICATION OF PLANTS:
According to various systems, the classifications of plants are as given below-

(a) Artificial System: - In this system, plants were classified on the basis of one or few convenient superficial characters. Pliny the Elder (79, AD) first of all give artificial system of classification.
- Theophrastus proposed first a kind of artificial system of classification on the basis of habit of plants. He classified them as herbs, shrubs, under shrubs, trees etc.
- C. Linnaeus (1707-1778) used artificial system of classification based only upon floral parts. The plants were classified as Hypogyny, Perigyny and Epigyny. It is also known as Sexual / Numerical System of classification. Linnaeus also classified plants on the basis of number and position of stamens. Plants with one stamen belonged to class Monandria and with 20 or more stamens to class Icosandria.He divided plants into 24 classes. Out of these, 23 classes were of Flowering Plants and 24rth class was of Flowerless plant(Cryptogamia). He published papers like Flora Laponica, Species Plantarum, Critica Botanicaa and Systema Naturae.
This system was inadequate. So, classification according to it was not accepted.

(b) This system is more common and divides plant kingdom into two sub-kingdoms Cryptogamae and Phanerogamae.
Sub-kingdoms were named on the basis of presence or absence of seeds / flowers.
Cryptogamae –(kryptos-concealed gamos-marriage) These included all non-flowering plants without seeds like Algae, Fungi, Lichens, Mosses and Ferns.
Phanerogamae- (Phaneros- visible gamos-marriage) or Spermatophytes (sperma-seed-phyton-plant)-These included all flowering plants with seeds.
Phanerogams can be distinguished from Cryptogams by presence of well-developed vascular tissue for conduction of water, minerals (xylem) and food (phloem). Plants with their vascular tissues resembling trachea (wind pipe) of animals are called Tracheophytes.

(5.2) THALLOPHYTA- ALGAE
1 - It includes both, Algae and fungi.
2 - Algae are usually aquatic, either marine (seaweed) or Fresh water. Few occur in moist soil. Wet rocks, moist tree trunks also. Fungi live in aquatic, sub-aquatic and terrestrial habitats.
3 -Body called ‘Thallus’ is unicellular flagellated (in Chlamydomonas), non-flagellat-ed (in Chlorella),colonial form (in Volvox) or filamentous (Ulothrix,Spirogyra).In some forms, it is flat and leaf like (Laminaria)and attaches to rock by structure called ‘Holdfast’. Fungi has branched Hyphae, which gets interwoven to form Mycelium.
4 -Algae are of different colours because of presence of different pigments in it. Green Algae has green pigments-Chlorophyll-a and Chlorophyll b in girdle /spiral shaped chloroplast. Brown pigment-Fucoxanthin, Red pigment-Phycoerythrin and blue pigment-Phycocyanin impart brown, red and blue colours to algae. Red Algae secretes and deposits calcium carbonate and appears like coral.E.g. of red algae are Polysiphonia,Gelidium, Batrachospermum.
5 - Algae show autotrophic nutrition. Fungi show heterotrophic nutrition.
6 -Algae reproduce vegetatively by fragmentation, budding or tubers. Asexual reproduction occurs by motile and non motile spores. Sexual reproduction occurs by Isogamy, Anisogamy and Oogamy.
7 -Life Cycle has distinct haploid and diploid phases, which alternate thus exhibiting Alternation of Generations.       On the basis of pigment colours, algae is further sub divided into Chlorophyceae (Green), Phaeophyceae (brown) and Rhodophyceae (red) Algae.

(5.3) BRYOPHYTA (Gk. Bryon-Moss     phyton-Plant)
1 . These occur in damp places, mostly during rainy season growing as green mat on rocks, soil, wall, tree trunks etc.
2 . Thalloid body is flat (Riccia) / liver shaped (Marchantia). So, these are also called as ‘Liverworts’.
3 . Some plants have body differentiated into stem and leaf like structure. Thallus is attached to soil, rocks, wall by root like structures called as ‘ Rhizoids’.
4 . Lack vascular tissues.
5 . Vegetative reproduction is very common and occurs by fragmentation, Gemmae and Tubers. Sexual reproduction involves male sex organs (Antheredium) and female sex organs (Archegonium).
6 . Life cycle has haploid and diploid phases. Haploid (Gametophytic) phase and diploid (Sporophytic) phase alternate with each other exhibiting Alternation of Generations’.
7 . Based on plant body and method of sexual reproduction, Bryophytes are sub-divided into Hepaticae (e.g.Marchantia) ,Anthocerotae (e.g. Anthoceros) and Musci (Funaria) Classes.

(5.4) PTERIDOPHYTA: (Pterido- Pteris    phyton-plant)
1 - Occur in humid and tropical climate on soil, rocks or on other plants. Equisetum grows near water bodies.
2 - Body has underground stem liske Rhizome having roots and aerial shoots with leaves. Some have simple leaves with single vein and some have compound leaves with several leaflets (pinnules).Compound leaves in Adiantum are arranged beautifully and look like maiden’s hair. So it is also called as ‘Maiden Hair Fern’.
3 - Sporangia occur on leaves in clusters called ‘Sori’. Spore bearing leaves are called ‘Sporophylls’.
4 - Vegetative reproduction occurs by fragmentation and budding. In ‘Walking fern’-Adiantum, new plant is produced wherever its leaf tip comes in contact with the soil.
5 - Plant body represents Sporophyte and is diploid. Spores are haploid and germinate on moist soil to form thallus like structure called ‘Prothallus’ which represents Gametophyte.
6 - Male sex organs (Antheridium) and female sex organs (Archegonium) help in sexual reproduction.
7 - Alternation of Generations is there. Dominant phase is Sporophytic.
8 - Pteridophyta is divided into 4 sub-classes-Psilopsida, Lycopsida, Sphienopsida and Pteropsida on basis of body organization, leaf structure and location of sporangia.
9 - Examples are-Dryopteris, Pteris, Lycopodium, Selaginella, Adiantum.

(5.5) GYMNOSPERMS: - (Gk. Gymnos-naked    sperma-seed)
1. Found in cool climate of hills. Some occur in warm climate also (Cycas).
2. These are generally tall woody trees. Few are bushes (Ephedra) or climbers    (Gnetum).
3. Have well developed vascular system of xylem and phloem,which helps in absorbing and conducting water in tall trees.
4 . Have no flowers but have seeds.
5. Leaf like structures called Sporophylls bear sporangia. Megasporophyll has Megasporangium (ovule). Microsporophyll has Microsporangium (pollen sac).Microsporophylls   and Megasporophylls form male cones and female cones respectively. Later, these   produce male and female gametes respectively.
6. After fertilization, zygote (2N) is formed in ovule, which ripens to form seed.
7. Alternation of Generation is there. Sporophyte is dominant phase.
8. These are further sub divided into 3 classes- Cycadopsida, Coniferopsida and Gnetopsida on the basis of nature of leaves, wood, vascular system & reproductive structure
9. Examples are Cycas, Araucaria, Ephedra, Gnetum, Pinus, Abies.

(5.6) ANGIOSPERMS: - (Gk. Angion- vessel   sperma-seed)- Flowering Plants.
(i)         Occur in diverse habitats and almost everywhere. These are trees, shrubs and herbs.
(ii)        Body is clearly differentiated into roots, stem and leaves.
(iii)       They have highly developed vascular system of xylem (with vessels) and phloem (With companion cells).
(iv)       Sporophylls are aggregated to form flowers. Stamens in flower represent microspor–ophyll whereas carpel represents megasporophyll.
(v)        Pollination occurs through several agencies like birds, animals, insects etc.
(vi)       After fertilization, ovule remains inside ovary, which later develops into fruit.
(vii)      These show Double Fertilization.
(viii)     Examples are sunflower, Maize, Wheat etc.

CLASSIFICATION OF ANGIOSPERMS: -

Most well known system of classification of Angiosperms was given by George Bentham (1800-1864) and Joseph Dalton Hooker (1817-1911). They published it in their book ‘Genra Plantarum’ (1862-1883)

Bentham and Hooker’s System :-It is based on form and relationship of plants. It is handy and accurate and covered about 97,000 species of seed plants. The Phanerogams were divided into classes, which were further sub divided into sub-classes. Sub-classes have ‘series’ which are further categorized into ‘Cohorts’ (equivalent to orders in other systems). Cohorts, further have ‘orders’ (equivalent to Families). There are total 202 orders (families). Few orders could not be placed properly in schematic arrangement and so ,because of their unusual position, these are called ‘Ordines Anomali’.

(Has 6 cohorts, 37 orders)         (Has 3 cohorts, 9 orders)           (7 orders)
Cohort I Ranales (8 orders)    Cohort I Rubiales (2 orders)        order130 Nyctaginaceae

Order1   Ranunculaceae            order 85 Caprifoliaceae        order131 Illecebraceae
Order 2 Dilleniaceae                     order 86 Rubiaceae                       order132 Amarantaceae
Order 3 Calycanthaceae              Cohort II Asterales (4 orders)    order133 Chenopodiaceae
Order 4 Magnoliaceae                  order 87 Valerianea             order134 Phytolaccaceae
Order 5 Annonaceae                 order 88 Dipsacaceae          order135 Batideae
Order 6 Menispermaceae          order 89 Calyceraeae            order136 Polygonaceae
Order 7 Berberideae               order 90 Compositae                    Series 2 Multiovulatae-
Order 8 Nymphaeaceae                 Cohort III Campanulales                  (3 orders)   Aquaticeae
Cohort II Parietales (9orders)       Order 91 Stylidieae                          (1 order)
Order 9 Sarraceniaceae               order 92 Goodeniaceae         order137 Podostemaceae
Order 10 Papaveraceae            order 93 Campanulaceae              Series 3 Multiovulatae-
Order11 Cruciferae                Series 2 Heteromerae                       terrestres
Order 12 Capparidaceae           (has 3 cohorts, 12 orders)                 (3 orders)
Order 13 Resedaceae                Cohort IV Ericales (6 orders)          order138 Nepenthaceae
Order 14 Cistineae                      order 94 Vaccinaceae                      order 139 Cytinaceae
Order 15 Violaceae                order 95 Ericaceae                           order140 Aristolochiaceae
Order 16 Canellaceae             order 96 Monotropeae                    Series 4 Microembryeae
Order 17 Bixineae   order 97           Epacrideae     (4 orders)

Cohort III Polygalineae (4 orders) order 141 Piperaceae
Order18 Pittosporeae             order 98 Diapensiaceae         order142 Chloranthaceae
Order 19 Tremandreae              order 99 Lennoaceae             order143 Myristicaceae
Order 20 Polygaleae                 Cohort V Primulales (3 orders)order144 Monimiaceae
Order 21 Vochysiaceae          order 100 Plumbagineae
Cohort IV Caryophyllineae (4 orders)                                    Series V Daphnales
Order 22 Frankeniaceae             order 101 Primulaceae               (5 orders)
Order 23 Caryophyllaceae            order 102 Myrsineae                       order145 Laurineae
Order 24 Portulaceae                   Cohort VI Ebenales (3 orders)order146 Proteaceae
Order 25 Tamaricaceae               order 103 Sapotaceae                      order 147 Thymelaeaceae
Cohort V Guttiferales  (6 orders)   order 104 Ebenaceae            order148 Penaeaceae
Order 26 Elatineae                      order 105 Styracaceae         order149 Elaeagnaceae
Order 27 Hypericineae                 Series 3 Bicarpellatae        Series VI Achlamydosporae
Order 28 Guttiferae                      (has 4 cohorts, 27 orders)                   (3 orders)
Order 29 Trenstroemiaceae          Cohort VII Gentianales (6 orders)order150 Loranthaceae
Order 30 Dipterocarpaceae        order 106 Oleaceae               order151 Santalaceae
Order 31 Chlaenaceae               order 107 Salvadoraceae      order 152 Balanophoreae
Cohort VI Malvales (3 orders)      order 108 Apocynaceae        Series VII Unisexuales
Order 32 Malvaceae                    order 109 Asclepiadaceae                      (9 orders)
Order 33 Sterculiaceae                 order 110 Loganiaceae             order 153 Euphorbiaceae
Order 34 Tiliaceae                       order 111 Gentianaceae           order154 Balanopseae
Series 2 Disciflorae (has 4 cohorts                                              order155 Urticaceae
21 orders & 2 anomalous orders) Cohort VIII Polemoniales           order156 Plantanaceae
Cohort VII Geraniales (has 11orders)              (5 orders)                  order157 Leitneriaceae
Order 35 Lineae                            order 112 Polemoniaceae         order158 Juglandeae
Order36 Humiriaceae                    order 113 Hydrophyllaceae       order159 Myricaceae
Order 37 Malpighiaceae                   order 114 Boraginaceae             order160 Casuarinaceae
Order 38 Zygophylleae                 order 115 Convolvulaceae         order161 Cupuliferae
Order 39 Geraniaceae                   order 116 Solanaceae             Series 8 Ordines Anomali
Order 40 Rutaceae                        Cohort IX Personales (8 orders)           (4 orders)
Order 41 Simaroubeae                  order 117 Scrophulariaceae       order162 Salicaceae
Order 42 Ochnaceae                     order118 Orobanchaceae          order163 Lacistemaceae
Order 43 Burseraceae                   order119 Lentibulariaceae     order164 Empetraceae
Order 44 Meliaceae                       order120 Columelliaceae          order165 Ceratophyllaceae
Order 45 Chailletiaceae                 order121 Gesneriaceae
Cohort VIII Olacales(has 3orders) order122 Bignoniaceae
Order 46 Olacineae                        order123 Pedaliaceae
Order 47 Ilicineae                          order124 Acanthaceae
Order 48 Cyrillae                           Cohort X Lamiales (5 orders)
Cohort IX Celastrales (has 4 orders) order125 Myoporineae
Order 49 Celastrineae                     order 126 Selagineae
Order 50 Stackhousieae                 order 127 Verbenaceae
Order 51 Rhamnaceae                    order 128 Labiatae
Order 52 Ampelideae (Vitaceae)       order 129 Anomalous-Plantagineae
Cohort X Sapindales (has 3 orders)
Order 53 Sapindaceae
Order 54 Sabiaceae
Order 55 Anacardiaceae

2 Anomalous orders

Order 56 Coriarieae
Order 57 Moringeae
Series 3 Calyciflorae                                7 Series of class Monycotyledonae
(Has 5 cohorts & 27 orders)                       Series 1 Microspermae (3 orders)
Cohort XI Rosales (has 9 orders)              order169 Hydrocharitaceae
Order 58 Connaraceae                                order 170 Burmanniaceae
Order 59 Leguminosae                                order 171 Orchidaceae
Order 60 Rosaceae                                     Series 2 Epigynae (7 orders)
Order 61 Saxifrageae                                  order 172 Scitaminae
Order 62 Crassulaceae                              order 173 Bromiliaceae
Order 63 Droseraceae                                order174 Hoemadoraceae
Order 64 Hamamelideae                           order175 Iridaceae
Order 65 Bruniaceae                                  order176 Amaryllidaceae
Order 66 Haloragaceae                             order177 Taccaceae
Cohort XII Myrtales (has 6 orders)         order178 Dioscoreaceae
Order 67 Rhizophoreae                                Series 3 Coronariae (8 orders)
Order 68 Combretaceae                               order179 Roxburghiaceae
Order 69 Myrtaceae                                     order180 Liliaceae
Order 70 Melastomataceae                            order181 Pontederiaceae
Order 71 Lythraceae                                    order 182 Philydraceae
Order 72 Onagraceae                                   order 183 Xyrideae
Cohort XIII Passiflorales (has 7 orders)          order184 Mayaceae
Order 73 Samydaceae                                   order185 Commelinaceae
Order 74 Loasaceae                                      order186 Rapataceae
Order 75 Turneraceae                                   Series 4 Calycineae (3 orders)
Order 76 Passifloreae                                    order187 Flagellarieae
Order 77 Cucurbitaceae                                order188 Juncaceae
Order 78 Begoniaceae                                   order189 Palmae
Order 79 Datiscaceae                               Series 5 Nudiflorae (5 orders)
Cohort XIV Ficoidales (has 2 orders)         order190 Pandanaceae
Order 80 Cacteae                                     order191 Cyclanthaceae
Order 81 Ficoideae                                  order192 Typhaceae
Cohort XV Umbellales (has 3 orders)         order193 Aroideae
Order 82 Umbelliferae                                 order194 Lemnaceae
Order 83 Araliaceae                                Series 6 Apocarpae (3 orders)
Order 84 Ceraniaceae                             order195 Triurideae
Order196 Alismaceae
Order197 Najadaceae
Series 7 Glumaceae (5 orders)
Order198 Eriocauleae
Order199 Centrolepideae
Order200 Restiaceae
Order201 Cyperaceae
Order202 Gramineae

CLASS I: Dicotyledons
- Seeds are with 2 cotyledons.
-Leaves have reticulate venation with alternate, spiral or whorled arrangement.
-Flowers are tetramerous or pentamerous (i.e. have four or five members in floral whorls).
-Vascular bundle is open type i.e. cambium present between xylem and phloem.
Class was further sub-divided into sub-classes on basis of no. and nature of floral whorls. On basis of position of ovary, sub-classes were further sub divided into series, which were further categorized into ‘cohorts’ (equivalent to order) and ‘orders’ (equivalent to Families).

(a) Sub-class: Polypetalae  (poly-free      petalae-petals)
-Corolla has whorl of 4-5 petals, which are free from one another. Calyx present.
-Sepals and petals are distinct and form two whorls.

Series (i) Thalamiflorae
-Many stamens, sepals and petals arising from thalamus above ovary.
-Ovary superior without any disc.
-Sepals are free from ovary.
-It has 6 cohorts and 34 orders. (See chart)

Series (ii) Disciflorae
-Flowers hypogynous, definite stamens.
-Ovary superior with nectariferous disc at the base.
-Sepals are either free (polysepalous) or fused (gamosepalous).
-It has 4 cohorts and 23 orders. (See chart).

Series (iii) Calyciflorae
-Flowers are perigynous or epigynous
-Inferior ovary.
-Sepals are fused and calyx forms a tube around ovary.
-Includes 5 cohorts and 27 orders. (See chart).

(b) Sub-class: Gamopetalae ( gamo-fused petalae-petals)
-Corolla has 4-5 petals, which are either partially or completely fused with one another.
-Sepals and petals are distinct.
-Stamens are attached to petals (Epipetalous).

Series (i) Inferae
-Stamens equal to the number of corolla lobes.
-Epigynous flowers.
-Inferior ovary.
-Has 3 cohorts and 9 orders. (See chart).

Series (ii) Heteromerae
-Stamens either equal to or twice the number of lobes of corolla.
-Stamens free from corolla.
-Hypogynous flower with more than two carpels.
-Superior ovary.
-Has 3 cohorts and 12 orders. (See chart).

Series (iii) Bicarpellatae
-Stamens less in number than corolla lobes.
-Two or more carpels with superior ovary.
-Hypogynous flower.
-Includes 4 cohorts and 24 orders.

(c ) Sub-class : Monochlamydae (Incompletae / Apetalae)
( mono-one    chlamydae-whorl)
-Incomplete flowers.
-Sepals and Petals are not distinct.
-Flowers have only one whorl with no petals. (Sepaloid).
-No cohorts.

Series (i) Curvembryae
-Embryo curved around the endosperm.
-One ovule.
-It has 7orders. (See chart).

Series (ii) Multiovulatae Aquaticeae
-Many ovules.
-Are submerged aquatic plants.
-It has 1 order.(see chart)

Series (iii) Multiovulatae Terrestres
-Many ovules.
-Terrestrial plants.
-Has 3 orders. (See chart).

Series (iv) Microembryae
-Minute embryo.
-Has 4 orders.(see chart)

Series (v) Daphnales
-Ovary with one carpel.
-Ovary with one ovule.
-It has 5 orders. (See chart)

Series (vi) Achlamydosporeae
-Inferior, unilocular ovary with 1-3 ovules.
-It has 3 orders. (See chart)

Series (vii) Unisexuales
-Unisexual flowers.
-Has 9 orders. (See chart)

Series (viii) Ordines Anomali
-Families of uncertain relationships.
-It has 4 orders. (See chart).

CLASS II- Gymnospermeae (Plants with naked seeds or seed plants without flowers).
This class is in between dicotyledons and monocotyledons. Some characters of it are: -
(i)         These are usually resinous trees or shrubs found predominantly in snowy, cold   regions. E.g. Cycas.Some are very large and live for thousands of years.e.g.Sequoia sempervirens.
(ii)        Leaves are needle like.
(iii)       These have well developed vascular system of xylem (without vessels) and Phloem(without companion cells).
(iv)       Flowers absent. Have two types of sporophylls-Microsporophylls & Megasporo-phylls. The two sporophylls form ‘Cones’- Male cones (Pollen cones) and Female Cones. (Seed cones).
(v)        Seeds are naked i.e. don’t occur inside fruit and lie exposed on surface of mega-sporophyll i.e. ovules are naked and don’t occur inside ovary.
(vi)       Pollination is direct and generally through wind.
(vii)      Male and Female gametophyte present.
(viii)     Male gametophyte forms two gametes, which show Double Fertilization.
(ix)       It has been divided into 3 families- Cycadaceae, Conifereae & Gnetaceae.
(x)        E.g. Cycas, Pinus, Ephedra, Araucaria, Cedrus.
(xi)       It includes 3 orders. (See chart).

CLASS III: Monocotyledons -These are usually herbs with simple large leaves showing parallel venation.
-Trimerous flowers i.e. floral parts exist in sets of three or its multiples.
-Embryo has one cotyledon.
-Primary roots are short-lived. Tap roots absent, Adventitious roots present.
-Vascular bundles scattered and closed type.
-E.g. Smilax, Colocasia, Banana, Palm, Grasses, Orchids, Bamboo, Lilies etc.
-These have been divided into 7 series on basis of nature of perianth and condition of Ovary

Series (i) Microspermae
-Petaloid perianth.
-Ovary inferior, unilocular with epigynous flower.
-Seeds minute, numerous and without endosperm.
-It has 3 orders. (See chart).

Series (ii) Epigynae
-Partly Petaloid perianth.
-Ovary inferior.
-Seeds are endospermic with nutritive tissue.
-It has 4 orders. (See chart).

Series (iii) Coronariae
-Petaloid perianth.
-Ovary superior and free.
-Seeds endospermic.
-It has 8 orders. (See chart).

Series (iv) Calycineae
-Perianth sepaloid.
-Ovary superior and free.
-Seeds endospermic.
-Includes 3 orders. (See chart).

Series (v) Nudiflorae
-Perianth absent or reduced to hair or scales.
-Ovary superior with solitary carpels.
-Endospermic seeds.
-Has 5 orders. (See chart).

Series (vi) Apocarpae
-Perianth with one or two whorls. Sometimes, it may be absent.
-Ovary superior. Carpels free.
-Endosperm absent.
-Has 3 orders. (See chart).

Series (vii) Glumaceae
-Perianth is either absent or is scaly or highly reduced.
-Unilocular ovary with single ovule.
-Has 5 orders. (See chart).

Merits of Bentham and Hooker’s System: -(i)   Every genus and species was studied from actual specimens and preserved herbarium sheets. Their description was based on detailed studies and dissections.
(ii) The descriptions given were easy to follow and were of practical utility for identification of species upto Family level. Information related to their geographical distribution was also given.
(iii) In the division Polypetalae, new series Disciflorae is put in between Calyciflorae and Thalamiflorae.
(iv) Unlike de Candolle, who distributed conifers among well defined taxas of dicots, Gymnosperms were considered a third taxon by Bentham and Hooker and placed in Between monocots and dicots.
(v) Genra was further sub-divided into sub-genra, which included important relevant sps. This made study more convenient.
(vi) Some aspects of system show affinity with modern concept of evolution. E.g. order Ranales is placed in the beginning and recent taxonomic studies have also established Ranales among the most primitive orders.
(vii) The placing of monocots after dicots is also according to evolutionary trends.

Demerits of Bentham and Hooker’s System:
(i) Placing of gymnosperms between dicots and monocots is anomalous.
(ii) Among dicots, Monochlamydae is considered highly evolved and Polypetalae as most primitive. Gamopetalae is placed in between the two. This is contrary to evolutionary trends.
(iii) Monochlamydae is not well-defined group as several families which have affinity with Polypetalae are included in it.
(iv) The placement of families like Asteraceae in beginning of Gamopetalae and Orchidaceae in Microspermae do not justify recent evolutionary trends.(v)        Some closely related families are kept apart.

RESPIRATION IN ANIMALS -

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:26:00 +0000

Respiration is the process of oxidation of food within the cells and tissues to form CO₂, water and ATP (energy). Energy is stored in the bonds formed between ADP and iP.
When respiration occurs in presence of oxygen, it is called as Aerobic Respiration. When respiration occurs in absence of oxygen, it is called Anaerobic Respiration Animals take in oxygen and release CO₂.

6.1 GASEOUS EXCHANGE IN ANIMALS :-

Main objective of respiration is to provide O₂ tissues and remove CO₂ from them. It occurs in different ways in different organisms like.
1 - Protozoans, Proiferans, Cnidarians respire through body surface. They take oxygen dissolved in water.

2 - Higher aquatic vertebrates like fishhave gilesfor exchange of gases.

3 - Terrestrial animals like amphibians, reptiles, birds, mammals have well developed lungsfor exchanging gases

4 - In Earthworms, respiration occurs by skin (body wall). Body wall surface is moist due to gland cells secretions and coelomic fluid. Body wall is richly supplied by blood which has respiratory pigment haemoglobin dissolved in it. Atmospheric O₂ differs into blood and gets circulated in tissues. CO₂ also diffuses out through body wall.

5 - In Cockroach, respiratory organs are highly branched air tubes called Trancheaewhich cover the entire body cavity (Haemocoel). Each tracheae opens outside by an opening called ‘Spiracle’ or stigmata. Cockroach has 10 pairs of stigmata (2 pairs are thoracic and 8 pairs are abdominal). There are 3 longitudinal tracheal trunks which are interconnected by transverse tracheae. Main tracheae branches repeatedly into smaller tracheae - (Tracheoles). Each spiracle is surrounded by Scleritewhich extends inwords and opens into atrium(Tracheal chanber).

Abdominal segment have tergo - sternal muscles which contract and relax rhythmically. This results in expansion and contraction of abdominal cavity. When it expands, air rushes in. when it contracts, air goes out. Gaseous exchange occurs between tissues and air present in the tracheses.

6.2- RESPIRATION IN HUMANS :

Respiratory system in humans is formed of two parts :
Respiratory Tract and B Respiratory organs.

(A) Respiratory Tract : It is the passage way for fresh air to flow from outside into lungs. It consists of:
1 - External Nares (Nostrils) :- It is a pair of opening at the end of nosc just above the mouth. It opens into naslal chamber.
2 - Nasal Cavity :- It is divided into 2 nasal chambers. It helps in warming, filtering and moistening the air.
3 - Internal Naras :- Nasal chambers open into nasopharynx by internal nares.
4 - Pharynx :- It is short tube behind the buccal cavity. It has three parts - nasopharynx (upper part), oropharynx (middle part) and laryngopharynx (lower part).
5 -Larynx : (voice box) :- A small tybular part present in the neck. Serves as connection between pharynx and Trachea. Glottis guards the opening of larynx.
6 -Trachea :- (Wind pipe) :- It is tubular structure, 12 cms long and 2.5 cms in diameter. It goes downwards and divides into right and left primary bronchi in the middle of thoracic cavity. Primary bronchi enters into lungs, divide and redivide to form secondary and tertiary bronchi, bronchioles. Bronchioles subdivide into many alveolar ducts which lead into alveoli or air sac. (B) Respiratory Organs :- These are a pair of lungs lying in thoracic / pleural cavity. A double layered pleural membrane protects the lungs. Pleural fluid is filled in the space between the two pleural membranes.

MACHANISM OF RESPIRATION :- It occurs in these steps :-
1. Breathing
2. Exchange of O₂ & CO₂
3. Transport of gases in the blood

1 - Breathing :- Breathing is Inspiration (intake of fresh air) and Expiration (expelling of foul air). The diaphragm, intercostals muscles and abdominal muscles play a role in this.
When diapmagm muscles and intercostals muscles contract sumuttareously, the volume of thoracic cavity increases. Thus pressure of air in the lungs decreases. The greater air pressure outside the body causes the air to flow in (Inspiration).
When lungs contract, their volume decreases. So air pressure in the lungs increases. Hence air is exhaled from the lungs (Expiration).During exercise, breathing rate increases as more O₂is required.

TIDAL VOLUME (TV) :- It is the volume of air inspired and expired with every normal breath. It is about 500 ml in an adult person.

INSPIRATORY RESERVE VOLUME (IRV) :- It is the extra amount of air that can be inspired forcibly after a normal inspiration. It is about 2500 - 3000 ml.

EXPIRATORY RESERVE VOLUME (ERV) :-It is the extra amount of air that can be expired forcibly after a normal expiration. It is about 1000 ml of air.

RESIDUAL VOLUME (RV) :- It is the volume of air which remains still in the lungs after the most forceful expiration. It is about 1500 ml.

PULMONARY CAPACITIES :- When two or more above mentioned pulmonary volumes are considered together, such combinations are called Pulmonary capacities.

INSPIRATORY CAPACITY (IC) :- It is the total volume of air that can be inhaled after a normal expiration.
IC = TV + IRV
IC is about 3000 - 3500 ml of air.

FUNCTIONAL RESIDUAL CAPACITY (FRC) :- Amount of air that remains in the lung after normal expiration is called Functional Residual Capacity. It is about 2500 ml of air.
FRC = ERV +RV

VITAL CAPACITY (VC):- It is the maximum amount of air that can be expelled from the lungs by forced exhalation after a forced inhalation.

VC ranges from 3400 - 4800 depending upon the age, sex and height of the individual.

2.Exchange of Gases :-
₂and CO₂ occurs in alveoli of lungs. O₂ in alveoli has higher partial pressure than in blood flowing in lungs. So O₂ diffuses from & alveoli into the blood. It passes into blood plasma and then combines with Haemoglobin of RBC to form Oxyhaemoglobin. CO₂ in lung capillaries have higher partial pressure than alveoli. So CO₂ diffuses from blood into alveoli after which it has to be expelled.
Alveolar mambrane is also called ‘Respiratory Membrane’as it is very then and contains rich network of blood capillaries which remain in contact with inspired air.

DIFFUSING CAPACITY :- The volume of gas that diffuses through respiratory membrane per minute for a pressure difference of 1 mm Hg.

3. Transport of Gases in blood :-
Blood is the medium of transportation of O₂ from lungs to tissues and CO₂ from tissues to lungs.
(a)Transport of Oxygen :-
(i) As dissolved gas :- 3% of O₂ in blood is dissolved in plasma which then carries it to body cells.
(ii) As Oxy haemoglobin :- About 97% of O₂ is carried in combination with Hb of RBC.

1 molecule of Hb can combine with 4 molecules of O₂. Under high partial pressure, O₂ binds with Hb in pulmonary capillaries. When this oxygenated blood reaches different tissues, the partial pressure of O2 declines, bonds between O₂ and HB become unstable and O₂ is released. Under normal conditions, opproximately 5 ml of O₂ is transported by 100 ml of blood. The amount of O2 that can bind with Hb is determined by Oxygen tension, which is expressed as partial pressure (Po₂).
At lower Po₂, Oxygen is released from Hb. Haemoglobin would be completely free from O₂ at zero Po₂. this relationship is expressed by plotting the oxygen saturation of blood against Po₂of oxygen. A S - shaped curve called ‘Oxygen - dissociation curve’ is obtained. It is dependent on Po₂, Pco₂, temperature and pH.

(b)Transport of CO₂ :-
(i) As dissolved gas :- About 7% Co₂ gets dissolved in blood plasma and is carried to the lungs. 0.3 ml of Co₂ is transported per 100 ml of blood.
(ii) As bicarbonate ions :- 70% Co₂ reacts with H₂O form carbonic acid in RBCs in presence of enzyme carbonic anhydrase.

H ₂CO₃dissociates to form bicarbonate ions and H⁺ ions.

Most of the HCo₃- diffuse into blood plasma to be carried by it.
(iii) As carbaminohaemoglobin :- About 23% of Co₂ entering RBCs combine with - NH₂ (amino) group of Hb to form carbamino - haemoglobin (HbCo₂).
Oxyhaemoglobin of RBC (HbO₂) is acidic and remains associated with K+ ions. Thus forming KHbO₂. H⁺ ions formed from dissociates from K⁺. Haemoglobinic acid (HHb) is formed.

CHLORIDE SHIFT /HAMBURGER SHIFT :-
Exit of Hco₃- ionic balance between plasma and RBC. To maintain this ionic balance, chloride ions diffuse from plasma into RBC. This movement of Cl - ions is called as ‘Chloride Shift’ or ‘Hamburger Shift’. It was reported by Hamburger in 1918.

RELEASE OF CO₂ IN ALVEOLI OF LUNGS :- Deoxygenated blood reaches alveoli of lungs. It contains Co₂ dissolved in plasma, as carbaninohaemoglobin and as Hco₃- ions. Co₂ is to be released in the lungs from these.
- Co₂ dissolved in plasma diffuses into alveoli.
- Carbaminohaemoglobin splits into Co₂ and Hb.
- Oxyhaemoglobin donates H+ which joins with Hco₃- to form H₂Co₃. H₂Co₃ then splits into H₂O and CO₂ in presence of enzyme carbonic anhydrase Co₂ is released.

6.3 REGULATION OF RESPIRATION :-
Respiration is under dual control :- Nervous and chemical.

(a)Nervous Control :- ‘Respiratory Centres’(group of neurons located in medulla oblongata of brain) control respiration. There are 3 respiratory centres :-
1 - Dorsal respiratory group :- located in dorsal portion of medulla oblongata. Signals from here are transmitted to diaphragm which helps in inspiration.
2 - Ventral respiratory group :- located in ventral portion o medulla oblogata. Remain inactive during normal respiration and become active only in enhanced respiration requirement. Signals from here control inspiration & expiration, both.
3 - Pneumotaxic centre :- located dorsally in upper pone. Controls the swithching off of inspiration. When this signal is strong, inspiration occurs for only 0.5 seconds and lungs are filled partially. When this signal is strong, inspiration occurs for only 0.5 seconds and lungs are filled partially. When this signal is weak, inspiration lasts for 5 seconds and lungs get fully filled.

(b)Chemical control :-
1 - Co₂ concentration :- Increase in Co₂ conc. in blood increases the respiration rate. Co₂ stimulates inspiratory as well as expiratory centres.
2 - O₂ concentration :- Conc. of O₂ doesn’t effect respiration directly.

6.4 RESPIRATORY DISORDERS :-1. BRONCHITIS :- It is the inflammation of bronchi which results in regular coughing and thick greenish yellow sputum. It occurs due to smoking or exposure to air pollutants like carbon monoxide.

2. BRONCHIAL ASTHMA :- It is caused by allergic reaction to foreign substances that effect respiratory tract. There are spasms of smooth muscles present in bronchiole wall. There is coughing and breathlessness. Exhaling is more difficult than inhaling.

3. EMPHYSEMA :- It is inflation / abnormal distension of bronchiole or alveolar sac which results in loss of elasticity of these parts. Lungs (Alveolar sac) remains filled with air even after expiration and so lung size increases. It occurs due to uigarette smoking or chronic bronchitis.

4. PNEUMONIA :- In this, alveoli become acutely inflamed. Fluid and dead WBC accumulate in lung tissues. It occurs mainly due to infection of bacteria Streptococcus pneumonial

5. OCCUPATIONAL LUNG DISEASES :- It is caused due to exposure of potentially harmful gases, fumes or dust present in the environment where a person works. eg. Silicosis (exposure to silica), Asbestosis (exposure to asbestos dust in mining). In it, inflammation occurs due to fibrosis of upper part of lung.

ANIMAL- NUTRITION

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:24:00 +0000

Nutrition is a process by which organisms obtain those substance which are utilized for their growth and maintenance and for meeting their energy needs. These substance are called Nutrients.

5.1 - FOOD AND NUTRIENTS OF ANIMALS:
Nutrients provide the metabolic energy and raw materials for growth , repair of tissues, production of gametes and protection from diseases.

TYPES OF NUTRIENTS:
1 - Macronutrients :Also called as ‘Proximate Principles of Food’. These are the main energy source for different body functions. e.g. carbohydrates, Lipids, Proteins.

2 - Micronutrients : Also called ‘Protective Principles of Food”. These do not provide energy but their deficiency causes diseases and abnormalities e.g. Minerals, Water, Vitamins

3 - Macroelements: Also known as’ Essential Elements’. These are 21 in number e.g. Na, K, S, Ca, P, Mg. These are essential for human body.

4- Microelements :Also known as ‘Trace elements’. These are required in very less amount e.g. Fe, I, Zn, Mn, Co, Cu, Mo etc.

5.2- MODES OF NUTRITION IN ANIMALS:
Animals have heterotrophic nutrition (i.e. they depend on others for food). Heterotrophic nutrition is of 4 major types:

(I) Holozoic: The mode of taking solid or liquid food through mouth is called holozoic nutrition e.g. in most of the animals, Man.
(II) Saprozoic: In this mode of nutrition , animals secrete digestive enzymes to dissolve decaying organic matter and then absorb it through their body surface e.g. in Fungi, Bacteria
(III) Parasitic: In this , one organism ( parasite) derives food from other organism ( Host) e.g.Plasmodium, Ascaris etc.
(IV) Symbiotic(Mutualism) : In this , two animals live in association with each other and derive nutrition from each other. e.g.E. coli lives in intestine of man and synthesize vit B₁₂ , which is beneficial to man. In returnE. coli receives simpler food from intestine.

TYPE OF HOLOZOIC NUTRITION
There are three main categories of holozoic animals:
* Herbivores: These are plant eating e.g. Cow, Horse.
* Carnivores: These are flesh eaters e.g. Lion, Dog.
* Omnivores: These eat plant and flesh both e.g. Man, Crow.
Other categories of holozoic animals are:
* Insectivores: Insect eaters e.g. Lizards.
* Frugivores: Fruit eaters e.g. Birds, Monkeys.
* Sanguinivores : feed on vertebrate blood e.g. Leech
* Fluid Feeders: Feed on plant fluid e.g. Butterflies.
* Predators: Larger animals feed upon smaller animals e.g. Eagle
* Grainivorous : Feed on grains e.g. Pigeon

STEPS OF HOLOZOIC NUTRITION
It involves following steps:
(i) Ingestion: Intake of food. Intake of microscopic organism is called Microphagy . Intake of larger organisms is called Macrophagy.
(ii)Digestion: Breaking of complex food components into simpler, soluble form by hydrolysis is digestion. It can be Intracellular i.e. occurring inside food vacuole in the cytoplasm of cell e.g. in Protozoans
OR
It can be Extracellular i.e. occurring outside the cell in a digestive cavity .e.g. in all vertebrates. In most animals, there is gastrovascular cavity lined by gland cells which secret enzymes to digest food.
(iii)Absorption: Digested food is absorbed in cell cytoplasm or in the cells lining the alimentary canal. This food is then absorbed in the blood.
(iv) Assimilation : Use of the simple food components to synthesize complex food components is assimilation.
(v) Egestion : Elimination of undigested food as faeces is egestion.

5.3 - DIGESTIVE SYSTEM OF COCKROACH:
It consists of alimentary canal & salivary glands. Cockroach are omnivores. Mandibles cut the food and then it is passed to buccal cavity, where it mixes with saliva. Then it enters into crop where teeth mince the food, then it reaches to gizzard. Lining of midgut and hepaticcaeca secretes various enzymes which digest the food. Food is absorbed in midgut . undigested food passes to hindgut & gets egested through anus.

DIGESTIVE SYSTEM OF HUMANS :
It is formed of two parts:-
(i) Alimentary Canal
(ii) Digestive Glands

1 - ALIMENTARY CANAL: It is coiled muscular tube about 6-9 metres in length. It comprises of
* Mouth: It is an opening bound by2 movable lips. It is meant for ingestion.
* Buccal Cavity ( Oral Cavity): Mouth leads into buccal cavity. Its roof is calledPalate. Posterior palate is hard and called ‘ Hard palate: Anterior part of palate is soft and is called soft palate . Oral cavity has tongue and teeth. Teeth are embedded in the two jaws ( lower jaw and upper jaw). Each half of the jaw holds 4 type of teeth ( Incisors, Canines, Premolars, molars)

Incisors( cutting teeth) are chisel shaped, sharp, pointed and meant for cutting. These are 8 incisors in all.

Canines( Tearing Teeth) are dagger shaped and meant for ripping and shredding. There are total 4 canines.

Pre-molars(Grinding/Cheek teeth) are broad teeth meant for crushing and grinding the food. There are total 8 premolars.

Molars( Grinding/ Cheek teeth) are also broad and meantfor crushing and grinding the food . These are 12 in number.

Dental Formula - It is formula representing the arrangement of teeth.2123 / 2123 or   I 2/2 , C 1/1, Pm 2/2 , M 3/3

Where I is incisor, C is Canine, Pm is Pre-molar , M is molars.

Human teeth arediphyodont ( 2 sets - milk & permanent)thecodont ( teeth embedded in jaw socket) andheterodont ( have different types of teeth).

Structure of Teeth: Human tooth has 3 parts- Crown( above the gum and is covered by hard enamel), Neck( fleshy and covered by gum) and Root( embedded in jaw socket). Both, crown and Root are covered by bony dentine . Inside, there is Central pulphaving nerve and blood supply.

Oral cavity leads to pharynx, then to oesophagus. Epiglottis guards the opening of trachea Oesophagus leads into stomach via diaphragm. Oesophageal sphincter guards the opening of oesophagus. Stomach has 3 regions - upper part ‘Fundus’, middle part ‘Body’ and lower part ‘ Pylorus’ or ‘Antrum’. Pylorus opens into small intestine. S. Intestine has 3 parts - Duodenum,Jejum and Ileum. S. Intestine leads into large intestine/colon. A vestigial organ- ‘caecum’ is present at the junction of s. intestine and large intestine. Finger like projection ‘Appendix’ emerges from the top of caecum. L. Intestine ascends from caecum as ‘Ascending colon’. Then crosses to left side as ‘transverse colon’ and descends again as ‘Descending colon’ Colon empties into rectum.

HISTOLOGY OF HUMAN GUT (Alimentary Canal)

Alimentary canal has four basic layers. These are ( from outside to inside)

(i)Serosa : Outermost layer, made of sequamous epithelium.
(ii) Muscularis externa: It is composed of outer longitudinal and inner circular muscle fibres.
(iii)Submucosa: It has dense connective tissue, richly supplied with blood vessels Mucosa>: It is innermost layer and has secretive and absorptive cells. It secretes mucus to lubricate the lining of gut.
(iv) Mucosa has numerous finger like projections called ‘villi’. Villi has blood capillaries and lymph vessels. ‘Central lacteal’ is the largest blood vessel. Villi has microvilli ( brush border) which increase surface area for absorption. Mucous glands or Goblet cells are present on surface of mucosa. These lubricate mucosal epithelium by secreting mucus. Sometimes epithelium invaginates into submucosa and forms pits . Pits of intestine are called ‘Crypts of Leiberkuhn’

THE ACCESSORY DIGESTIVE ORGANS:
Tongue is an accessory digestive organ. It is located in buccal cavity by bones- styloid and Hyoid. Gustatory receptors called ‘ Taste buds’ are present on the tongue. The accessory digestive glands are
1 - Salivary Glands: There are 3 pairs of salivary glands-Parotid glands( in the cheek), Sublingual ( beneath the tongue) and submandibular ( at the angles of lower jaw). These secrete saliva.
2 - Liver: It is the largest gland of the body, is located in the upper right side of abdominal cavity just below the diaphragm.
3 - Gall Bladder: Pear like structure located below liver . It stores bile secreted by liver.
4 - Pancreas: It is an elongated gland lying partly behind the stomach in abdomen

MOBILITY OF HUMAN GUT
The ability of alimentary canal to contract is called ‘Mobility’. Food moves along the length of alimentary canal so as to get digested and absorbed. First the food is tasted ( in mouth), then it mixes with saliva. Tongue helps the food to mix with saliva. And the form a round structure- bolus. Bolus is pushed into oesophagus by process of swallowing. During swallowing , openings of nasal passage & trachea are closed by epiglottis. A contraction wave called ‘Peristalsis’ pushes the food down. Then bolus enters stomach. The sphincter at the junction of oesophagus and stomach closes so that the food doesn’t go back.

GASTRO INTESTINAL SECRETION AND DIGESTION:
The secretions from salivary glands, secretary cells in stomach, secretary cells of Pancreas and liver help in digestion. Group of enzymes called ‘ Hydrolases’ break the food and the process in Hydrolysis. The phases are:-
* Salivary Phase: Occurs in buccal cavity. Salivary glands secrete saliva which contains enzymes (Ptyalin and Maltase) and ions.
- Enzyme Ptyalin ( a-Amylase) acts on starch and breaks it into maltose.
- Enzyme Maltase acts on Maltose and converts it into glucose.
- Bicarbonate ions in saliva neutrilize acids of food.
- Thiocyanate ions of saliva act as antimicrobial agents. Food passes into stomach from buccal
cavity.

* Gastric Phase: Takes place in stomach . Food is acted upon mechanically and chemically. Mechanically, wall of stomach undergoes rhythmic contractions and breaks the food.
Chemically, food is acted upon by gastric juice secreted by gastric glands of the stomach. Gastric juice contains:-
- HCl:- Secreted by oxyntic ( parietal) cells. Acts as disinfectant and activator of proenzymes.
- Propepsin:-It is inactive form . It is converted into active form Pepsin by HCl. It breaks   proteins into proteoses and peptones.
- Mucus : Secreted by goblet cells present in epithelium of stomach. Acts a lubricant.
Semidigested food called ‘Chyme’leaves the stomach and enters duodenum.

* Intestinal Phase: It takes place in small intestine . There are three juices: Bile juice ( from liver), Pancreatic juice ( from pancreas) and Intestinal juice ( from intestinal glands).

-Bile Juice : It is stored in gall bladder, reaches to small intestine by bile duct . It contains water, cholesterol, bile salts, bile pigments and phospholipids. Bile salts ( Na₂CO₃, Sodium taurocholate, Sodium glycocholate) emulsify the fat i.e. break bigger fats into smaller fat droplets. Bile ligments ( Biliverdin & Bilirubin) are the wastes products of breakdown of Hb and are excreted out along with faces. - Pancreatic Juice: It secreted by Acinar cells of Pancreas. It reaches intestine through pancreatic duct. It contains proenzymes.
Trypsinogen - It is inactive form and is converted into active form Trypsin by enzyme Enterokinase of intestinal juice. It converts proteins→ polypeptides.
Chymotrypsinogen- It is inactive form. Active form Chymotrypsin is formed by action of trypsin. Its function is same as Trypsin.
Procarboxypolypeptidase : Inactive form , Active form Carboxy Polypeptidase is formed by trypsin. It breaks polypeptides into amino acids. - Intestinal Juice : ( Succus Entericus). It is secreted by two glands, Crypts of Leiberkuhn and Brunner’s Glands. Cryts of Leberkuhn secrete digestive enzymes and mucus. Brunner’s Glands secrete little enzyme and mucus.
Secretion of intestinal glands is called Intestinal Juice. It contains enzymes like Maltase, Sucrase, Lactase, Aminopeptidase, Enterokinase, nucleotidase, Nuclease, nucleosidase, lipase.

Goblet cells secrete mucus which protects duodenal wall from getting digested.

5.5 - HORMONAL CONTROL OF DIGESTION IN HUMANS:
Hormones control the secretion of juice during digestion.

(i) Salivary Phase : It is under nervous control ( Sympathetic and Parasympathetic nerves). Hormones don’t control this phase.
(ii)Gastric Phase: It is under nervous hormonal , chemical and mechanical control. In hormonal control, Pyloric epithelium secrets hormone Gastrin when food reaches the stomach . It reaches glands ( via blood) which release gastric juice.
(iii)Intestinal Phase: Bile secretion is controlled by hormones Cholecystokinin. Secretin hormone controls pancreatic juice secretion. Gastric Inhibitory Peptide ( GIP) homone inhibits gastric secretion . It is secreted by upper small intestine. Hormones Duocrinin and Enterocrinin control intestinal juice.

5.6 - ABSORPTION AND ASSIMILATION OF DIGESTED PRODUCTS IN HUMANS:

Absorption is the process by which nutrients pass from alimentary canal into blood and lymph.
Assimilation is the process by which absorbed food becomes a part of protoplasm and is used for energy, growth and repair.
No absorption occurs in buccal cavity, very little occurs in stomach and all the absorption occurs in small intestine. Projections villi and microvilli help in absorption. There are two type of absorption process : Passive & Active absorption. Passive Absorption : Nutrients are absorbed along the concentration gradient . It occurs by processes like Diffusion ( Fatty acids, monoglycerides, cholesterol, fat soluble substances are absorbed by this) , Osmosis (e.g. water & water soluble substances) and Facilitated Diffusion ( e.g. Fructose). In facilitated diffusion , carrier proteins carry the nutrients. Active Absorption: It is independent of concentration gradient, is brought by carrier proteins and utilizes energy derived from hydrolysis of ATP. Glucose, Galactose , Amino acids, Na+ are absorbed by this method. For Na+ absorption, a sodium pump operates in cell membrane. Absorption of Fats: It occurs differentially. Products of lipid digestion ( e.g. long chain fatty acids , monoglycerides, diglycerides) are insoluble in water and can’t be directly absorbed. So these combine with bile salts & phospholipids to form small spherical, water soluble molecular aggregate called ‘Micelles’. From micelles, fatty acids, glycerides, sterols and fat soluble vitamins are absorbed into intestinal cells by diffusion.

Here they are resynthesized into very small fat droplets ‘Chylomicrons’ which are released in lymphcapillaries called ‘ Lacteals’

.Assimilation : In this absorbed food are utilized e.g. Amino acids are utilized for synthesis of proteins. Glucose provides fuel and energy for metabolism fats from cellular biomembranes , act as fuels etc.

5.7 - EGESTION: The elimination of undigestible remains of food from alimentary canal is called ‘Egestion’. The undigested food along with water and excessive digestive enzymes enters large intestine. Colon absorbs water and concentrates undigested food into faeces. Faeces are temporarily stored in rectum where more water is absorbed. Then faeces are expelled through anus. Muscles of large intestine, abdomen and diahragm contract to expel faeces. Muscles of anal sphincter relex to expel faeces.
Composition of Faeces : 75% water, 25% solid matter. Solid matter is formed of undigested roughage ( 30%), fats ( 20%), inorganic matter( 15%) , Proteins (3%) and bacteria (3%). Bacteria is E. coli

5.8 - NUTRITIONAL REQUIREMENTS OF HUMANS:
Food contains carbohydrates, lipids, proteins minerals, vitamins and water. Carbohydrates, lipids and protein provide energy. Minerals , water and vitamins do not provide energy.

ENERGY YIELDING NUTRIENTS

1 - Carbohydrates: These provide energy and are stored in body cells as Glycogen. Synthesis of Glycogen is called Glycogenesis. Production of new glucose is called Gluconeogenesis e.g. during starvation liver converts aminoacid & glycerol into glucose.
2 - Proteins: Proteins provide energy on their breakdown into amino acid. Essential aminoacids are essential for body but are not synthesized in the body so these must be obtained from outside . An average person needs 70-100 gms of proteins daily. About 15% of human diet should be formed of proteins.
3 - Fats:– These are concentrated energy reserves. Adipose tissues can store upto 95% of their volume of fats. So these are called ‘Fat Depot’ of body. Essential Fatty acids are taken in diet. These are linoleic acid, linolenic acid and arachidonic acid. An adult needs about 100 gms of fat on an average CALORIE VALUE:– Heat is the ultimate form of energy. So energy requirement of animals and energy content of food is expressed as ‘Calorie’ (cal) or ‘Joule’(J). It is the amount of energy required to raise the temp of 1gm of water by 1°C. Commonly it is called ‘Kilocalories’ (1 kcal = 1000 cal) or ‘Kilojoule’ (1 kJ = 1000 J), which is the amount of energy required to raise the temp of 1 kg of water by 1°C.
GROSS CALORIFIC / GROSS ENERGY VALUE:– It is the amount of heat liberated from complete combustion of 1g food in bomb calorimeter in the laboratory
Physiologic Value:– The amount of energy liberated in human body due to combustion of 1g of food is called physiologic value

Nutrient                           Gross calorific value                          Physiologic value
Carbohydrate                   4.1 kcal/g                                             4.0 kcal/g
Proteins                            5.65 kcal/g                                           4.0 kcal/g
Fats                                  9.45 kcal/g                                           9.0 kcal/g

4 - Minerals:– These are taken in as salts dissolved in water or as part of organic compound. Major Minerals are important to the body 0.1 gm of each of these minerals is required everyday. Trace minerals are required in lesser amount. 0.01 gm of each trace mineral is required everyday
e.g of essential minerals are Ca, Cl, P, K, Na, S, Mg
e.g, of trace minerals are Cu, I, Fe, Zn, F, Mn, Mo, Cr, Co, Zn

5 - Vitamins:– These are the organic substances required for normal growth and metabolism of the body and are taken from outside. These do not provide energy. Some vitamins are fat soluble (eg Vitamin B complex, vit C). Vit. D is synthesized in the skin in the presence of ultraviolet rays of sun.

5.9 - NUTRITIONAL DEFICIENCIES AND DISORDERS:–
Deficiency of vitamins, minerals proteins etc. causes disorders, diseases and abnormalities in humans
MALNUTRITION:– Improper intake of food or nutrients causes impairment of health called-Malnutrition Malnutrition can be undernutrition or overnutrition Excess intake of saturated fats (butter, ghee, vegetable oil, eggs etc) causes Hypercholesterolemia in which blood. Cholesterol level becomes very high causing cardiac disorder Overweight and obesity are also results of overnutrition

RESPIRATION IN PLANTS

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:15:00 +0000

Light energy is converted into chemical energy in photosynthesis. This energy is stored in the bonds of molecules like carbohydrates e.g, Glucose, Starch.
The oxidation of various organic molecules to release energy for cellular use is called as Respiration. It is stepwise process controlled by enzymes.
Respiratory Substrates:- Compounds which get oxidized. The reaction during respiration, when glucose acts as a substrate is:-
C₆H₁₂O₆ + 6O₂  6CO₂ + 6H₂O + Energy (2870 kJ).

4.1 TYPES OF RESPIRATION:- Cellular respiration is of two types depending on the availability of oxygen -
(a) Aerobic Respiration - Oxygen is present
(b) Anaerobic Respiration - Occurs in absence of O₂

(a) Aerobic Respiration:- It uses O₂. The organic food is completely oxidized to CO₂ and H₂0. Energy is released. Organisms showing this respiration are known as 'aerobes' or 'aerobic organisms'. It occurs in higher organisms

(b) Anaerobic Respiration:- It does not use O₂. The organic food is incompletely oxidized into carbonic compounds (like ethylalcohol, acetic acid, lactic acid) and CO₂. Small amount of energy is released organisms having this type of respiration are called 'anaerobes' or 'anaerobic organisms'. It is seen in lower organisms and higher plants

4.2 RESPIRATORY RATIO / QUOTIENT ('RQ'):- It is the ratio of volume of CO₂ produced to the volume of O₂ consumed during respiration over a period of time its value can be 1, zero, more than 1 or less than 1 and depends upon the substrate used.

The value of RQ for different substrates is:-

(i) Carbohydrates:-
C₆H₁₂O₆ + 6O₂  6CO₂ + 6H₂0 + Energy

RQ = 1

(ii) Fats:-
2C₁₅H₉₈O₆ + 145O₂  102CO₂ + 98H₂0 + Energy Tripalmitin

RQ = 0.7

(iii) Organic acids:- 2(COOH)₂ + O₂  4CO₂ + 2H₂0 + Energy oxalic acid

RQ = 4

(iv) In anaerobic respiration, there is no consumption of O₂, CO₂ is produced, carbohydrate is the usual substrate CO₂ is produced. Carbohydrate is the usual substrate.
C₆H₁₂O₆  2CO₂ + 2C₂H₅OH + Energy
RQ = 2CO₂/O
RQ = Infinity (  )

(v) Succulents do not evolve CO₂ during night. They also convert carbohydrates to organic acids during which O₂ is used but CO₂ is not evolved.
2C₆H₁₂O₆ + 3O₂  3C₄H₆O₅ + 3H₂0

RQ = Zero

PHOTOSYNTHESIS

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:10:00 +0000

Photosynthesis is the most important anabolic process by which green plants / autotrophic organisms synthesize complex carbohydrates from CO₂ and H₂O with the help of light energy. Green pigment chlorophyll is required for this process. Photosynthesis is performed by chloroplast.

3.1 HISTORY OF PHOTOSYNTHESIS :
- Aristotle and Theophrastus (320 B.C.) believed that plants obtain all their nourishment from the soil.
- Jan Baptista Van Helmont (Belgian Physician) in 1648, concluded by his experiment that weight of plant increases due to water absorbed and not due to soil.
- Stephen Hales (1727) discovered that green plants require sunlight and air for their nutrition.
- Joseph Priestley (1733 - 1804) showed that plants take up CO₂ from the atmosphere and release O₂
- Jan Ingenhousz (1730-1799) confirmed Priesteey's work. He discovered that O₂ was released only in sunlight and only by green parts of plant.
- Theodore de Saussure (1804) found that water is essential for photosynthesis.
- Pelletier and Caventon (1818) discovered and named the green pigment 'chlorophyll'

EQUATION FOR PHOTOSYNTHESIS : It was given by C.B. Van Niel of Stanford University, U.S.A.

The above simple equation is now written as :

3.2 SITE FOR PHOTOSYNTHESIS :
It occurs in green parts of the plant, mostly leaves. Leaves have specialized cells - Mesophyll cells which contain Chloroplasts. Chloroplasts are the actual sites of photosynthesis. The thylakoids in the chloroplast contain most of the machinery for photosynthetic reactions, like pigment- chlorophyll. A pigment is a substance which absorbs light of different wavelengths.
Chlorophyll absorbs light in violet, blue and red wavelengths of visible spectrum of light. This portion of spectrum ranges from 400 nm - 700 nm, and is called as 'Photosynthetically active radiation' (PAR).

STRUCTURE OF CHLOROPHYLL :
It is main photosynthetic pigment, is green in colour and is of many types. It can be chl-a, b, c, d, e bacteriochlorophyll a, b, c, d, e and bacterioviridin. Bacteriochlorophyll is found in bacteria. Chl-a & b are widely found. Chl - c, d, e occur in certain algae.
Chl -a is made up of four Pyrrole rings and a central core of Mg. Each pyrrole has 4 carbon atoms and 1 Nitrogen. This tetrapyrrole ring is called 'Porphyrin Head'
'Phytol tail' is attached to porphyrin head. Phytol tail is made of 20 carbon alcohol attached to carbon 7 position of pyrrole ring 4. So one pyrrole ring gets esterified with alcohol (C₂₀H₃₉,OH).

When chl - b absorbs light, it gets excited and transfers its energy to chl - a molecule. Chl - a converts light energy to energy. Thus chl - a acts as Reaction Centre.
Accessory Pigments like carotenoids also capture light and transfer it to reaction centers for conversion to electrical energy.
Reaction centres and Accessory pigments, together, form 'Photosystem'

3.3 PHOTCHEMICAL & BIOSYNTHETIC PHASES :
A photosynthetic unit is the smallest group of pigment molecules which take part in a photochemical reaction. It has a 'reaction centre' which is fed by 'pigment molecules'. Main pigment is chlorophyll (chl) which occurs in many forms like chl-a. Chl -a has further many forms depending upon the wavelength which shows absorption peak. eg : chl-a 673 (shows absorption peak at 673 nm), chl-a 683 (P₆₈₀) - shows absorption peak at 683 nm : chl-a 703 (P₇₀₀) -shows absorption peak at 703 nm. 'P' stands for pigment. These pigments occur in thylakoids as units called 'Photosystems'. A photosystem has 250-400 pigment molecules. There are 2 types of photosystems:
PSI and PS II.
PSI is located in storma & grana of chloroplast, has chl-700 (P₇₀₀) as reaction centre and comprises of 200-400 chlorophylls.
PS.II is located in grana, has chl-683 (P₆₈₃) as reaction centre, consists of about 200 chlorophyll molecules.
Both systems, PSI & PSII interact with each other, trap light energy, convert it into chemical energy which is then stored as ATP.

ELECTRON TRANSPORT CHAIN :
Electron Transport chain includes the photosynthetic reactions initiated by light. It was formulated by Robert Hill in 1939.
P₆₈₀ (PSII) absorbs light and gets excited. It transfers its electrons to an electron accepting molecule and becomes an oxidizing agent. Then it splits a water molecule to release O₂. This splitting is called Photolysis. Mn²⁺, Ca²⁺ and Cl ^- play a role in it. Electrons generated in this process are picked up by P₆₈₀ again. Then it donates these electrons to downstream components in electron transport chain.
Similarly, PSI(P₇₀₀) absorbs energy, gets excited and transfers its electron to primary electron acceptor. Thus P₇₀₀ gets oxidised. Reduced electron acceptor transfers its electrons to Ferredoxin and Ferredoxin-NADP reductase to reduce NADP to NADPH₂. NADPH₂ reduces CO₂ to carbohydrates in the presence of ATP which is produced during ETS.

PHOTOPHOSPHORYLATION : During electron transfer in ETS, some energy released is used up in the synthesis of energy rich compounds like ATP from ADP and ip (inorganic Po₄). The production of ATP from ADP in th presence of light is called Photophosphorylation.

Photophosphorylation occurs by two ways :
(i) Non - cyclic
(ii) Cyclic

(i) NON-CYCLIC PHOTOPHOSPHORYLATION :
In this, the electron flow is unidirectional and electrons released by pigment of PSI and PSII are never received back. ATP is produced.
Electrons flow from water to pigment of PSII, then to pigment of PSI and finally to NADP.

(ii) CYCLIC PHOTOPHOSPHORYLATION :
It involves only PSI and the electrons received from PSI are returned back to it. Cyclic phosphorylation takes place when non-cyclic photophosphorylation can be stopped by illuminating chloroplast of PSII with light of wavelength more than 680 nm. Thus electron from H₂O to NADP stops. CO₂ fixation stops. NADPH is not oxidised & so NADP is not available. As NADP is not available, electrons from PSI are not passed to NADP and instead transferred back to P₇₀₀.

BIOSYNTHETIC PHASE :
ATP & NADPH₂ are essential for conversion of CO₂ to carbohydrates. These reactions occur in stroma of choloroplast and are called as 'Carbon Reactions' (or Dark Reactions).
Dark reaction can occur by C₃ pathway which is also known as Calvin cycle.

CALVIN CYCLE (C₃ pathway) : The complete sequence of reactions were given by Melvin Calvin and Benson. They worked on algae Chlorella. The steps are :

(i) Carboxylation : 6 molecules of Ribulose -5-PO₄ react with 6ATP.
6 Ribulose -5-PO₄ + 6ATP  6 Ribulose 1-5 diPO₄ + 6 ADP.
- 6 Ribulose -1-5 diPO₄ react with 6CO₂ and 6H₂O to form 3 Phosphoglycerate (PGA). PGA is the first 3-C stable product, so this pathway is called C₃ pathway.
- 6 Ribulose -1-5 diPO₄ + 6CO₂ + 6H₂O  12 PGA
- Enzyme acting is Rubisco (Ribulose bisphosphate carboxylase oxygenase)

(ii) Reduction of PGA :
- 12 molecules of 3 PGA are reduced to 12 molecules of 3 PGAL (Phosphoglyceraldehyde) by using 12 NADPH₂ & 12 ATP.
12 3 PGA + 12 NADPH₂ +12 ATP  12 3 PGAL + 12 ADP + 12 NADP + 12 iP +12 H₂O.
Enzyme - Dehydrogenase Kinase.
- 3 PGAL is isomeric with dihydroxyacetone 3PO₄.

(iii) Formation of Hexose sugar :
- 3 molecules of 3 PGAL and 3 molecules of dihydroxyacetone 3 PO₄ combine to form 3 molecules of Fructose 1-6 diPO₄.
3 PGAL + 3 dihydroxyacetone 3PO₄  3 Fructose 1-6 diPO₄.
Enzyme - Aldolase.
- Fructose 1-6 diPO₄ converts to fructose -6PO₄ by removing iP.

(iv) Regeneration of Ribulose -5-PO₄ :
1. Remaining 2 molecules of Fructose -6PO₄ combine with 2 molecules of PGAL to form Erythrose -4PO₄ and Xylulose -5PO₄.
2 Fructose -6PO₄ + 2 PGAL  2 Erythrose - 4PO₄ + 2 xylulose 5 PO₄

2.

3. Each Sedoheptulose 1-7 diPO₄ looses its PO₄.

4. 2 Sedpheptulose 7 PO₄ combine with 2 remaining molecules of PGAL.
2 Sedpheptulose -7 PO₄ + 2 PGAL  2 Ribose - 5PO₄ + 2 Xylulose -5-PO₄

5.
2 Ribose 5PO₄ is isomeric with 2 Ribulose -5PO₄.

6. 4 molecules of xylulose 5 PO₄ are isonmerised

Thus, 6 molecules of Ribulose 5 PO₄ are regenerated during C₃ cycle.

3.4 C₄ PATHWAY : (Hatch and Slack Cycle)
It was worked out by Hatch & Slack (1965, 67), so it is also called Hatch & Slack cycle. They found that in several plants like sugarcane, Maize, the first stable product of CO₂ fixation is Oxaloacetic acid which is a 4-carbon compound. So it is also known as C₄ pathway and such plants are called as C₄ plants.
C₄ plants are found is tropical / sub tropical regions, their leaves have Kranz anatomy, these have dimorphic chloroplast (i.e. chloroplast in mesophyll cells are granal and in bundle sheath cells are agranal).

Mechanism : The reactions are :
1. In mesophyll cells : (i) Phosphoenol pyruvic acid (PEP) combines with CO₂ to form a stable 4-C compound - oxaloacetic acid.

(ii) Oxaloacetic acid is reduced to Malic acid.

2. In bundle Sheath cells :
(i) Malic acid is transported to bundle sheath. Here it is decarboxylsed to form Pyruvic acid.

(ii) CO₂ enters into calvin cycle, combines with Ribulose, 5 diPO₄ to form Phosphoglyceric acid and hexose sugar.

3. In mesophyll cells :
Pyruvic acid returns to mesophyll cells where it is converted back to phosphoenol pyruvic acid.

3.5 CRASSULACEAN ACID METABOLISM : (CAM PATHWAYS) :
Succulent plant fix CO₂ in dark. These plants grow in semi arid conditions. It is called CAM pathway because it was observed first in plants of family Crassulaceae eg. Bryophyllum
It occurs in 3 steps :
1. Acidification : During dark (night), CO₂ is absorbed from outside. Primary acceptor is phosphoenol pyruvic acid (PEP).

2. De - acidification : In presence of light, organic acids move out of vacuoles and CO₂ is released. High temperature favours it.

3. Calvin Cycle : Released CO₂ is taken by Ribulose 1-5 diPO₄ to perform Calvin cycle.
CAM pathway is an adaptation in certain plants to carry out photosynthesis without much loss of water.

3.6 FACTORS AFFECTING PHOTOSYNTHESIS :
Photosynthesis is influenced by environmental as well as genetic factors. But according to F.F. Blackman, photosynthesis is limited (influenced) by the slowest step in pathway. This became popularly known as Blackmans Law of Limiting Factors (FF Blackman, 1905) ( or Principle of Limiting Factors). It states that :
"When a process is conditioned as to its rapidity by a number of separate factors, the rate of process is limited by the pace of the slowest factor".
Various factors controlling photosynthesis are :

1. LIGHT : Light intensity, Light quality and Light duration effect photosynthesis rate. As the intensity of light increases, the rate of photosynthesis also increases. Light wavelength between 400nm-700nm is most effective. This is called Photosynthetically active radiation (PAR). At higher light intensities, rate of photosynthesis decreases because chlorophyll gets destroyed and other factors become limiting.
Light quality : Blue & Red light are the best for photosynthesis
Light duration : Average light of 10-12 hrs/day results in higher rate of photosynthesis.

2. CO₂ : Conc. of CO₂ in atmosphere is 0.03% or 360 ppm. Increase in conc. upto 0.1% increase the rate of photosynthesis
Above 0.1%, the photosynthesis rate declines.
When conc. of CO₂ is reduced, then 'Compensation point' or 'Threshold value' is reached at a certain stage when CO₂ fixed in photosynthesis becomes equal to CO₂ evolved in respiration and photorespiration. At this point, plants stop absorbing CO₂ from atmosphere. This value is 50-100 ppm in C₃ plants and 0-10 ppm in C₄ plants.

3. Soil Water : Water deficiency decreases rate of photosynthesis as plants undergo water stress, stomata close, CO₂ supply decreases and leaf expansion decreases. This reduces the photosynthetic surface area.

4. Nutrient supply : Most important nutrient is Nitrogen as it is constituent of chlorophyll and many enzymes. All essential elements effect rate of photosynthesis.

5. Temperature : Optimum temp. is 20-35⁰C. Above this temp, rate of photosynthesis shows initial increase and then it declines with time. Temp does not influence light reaction but affects enzyme-controlled dark reactions. At higher temperature, enzymes are destroyed.

6. Leaf factors : Rate of photosynthesis increases with the age of leaf till it becomes maximum at full maturity. After that, it declines.
If leaf turns yellow (loss of chlorophyll), Photosynthesis stops.
Hormones (Cytokinins, Giberellins) increase the rate and Abscisic acid reduces the rate of photosynthesis.

3.7 TRANSLOCATION OF PHOTOSYNTHESIS :
Energy rich compounds formed during photosynthesis (Photosynthates/Photoassinilates) are transported out of leaf to roots, stem, developing seeds and grains. This is called Translocation. It occurs through phloem.
Sucrose is the main form of carbohydrate which is translocated . It is non reducing sugar and is stable chemically (i.e. does not react with other substances during translocation).

3.9 SIGNIFICANCE OF PHOTOSYNTHESIS :
1. It links physical and biological world by converting solar energy into organic matter which is the bulk of a living organism. 2. It produces O₂ which is vital for life. 3. Agricultural productivity depends on photosynthesis.

3.9 CHEMOSYNTHESIS : Some aerobic bacteria do not require light for carbohydrate synthesis. They do so by using energy from chemical reactions.
The process of carbohydrate synthesis, in which organisms use chemical reactions to obtain energy from inorganic compounds is called Chemosynthesis.
eg.Bacteria Nitrosomonas oxidizes NH₃ to nitrite. Energy released during the reaction is used by bacteria to convert CO₂ to carbohydrates. These bacteria are called Chemosynthetic autotrophs.

PLANT NUTRITION

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:08:00 +0000

All living organisms require nutrients for their growth and development. Organisms which can make their own food are autotrophs e.g, Plants. Organisms which cannot make their own food and depend on auto – trophs for food are called Heterotrophs. Plants obtain their nutrients (minerals) from soil. This is known as Mineral Nutrition.

2.1 Essential Mineral Elements:–
Elements which are required essentially for plants growth and development are called. ‘Essential Mineral Elements’
The criteria for essentiality of an element is:
(i) It should be absolutely necessary for supporting normal growth & development of plant
(ii) The element required should be specific
(iii) The element cannot be replaced by any other element
(iv) The element must be directly involved in metabolism of the plant. Total 105 elements are there, out of which 20 are essential for the plant. Essential elements are divided into two categories:–
1- Macro nutrients
2 - Micro nutrients

Macronutrients are the nutrients present in larger quantity in the plants. Their concentration are 1 – 10 mg per gram of dry matter e.g, C, H, O, N, P, S, K, Ca, Mg, Si.
Micronutrients are nutrients present in smaller amounts i.e, less than 0.1 mg per gram of dry matter e.g, Fe, Zn, Mn, Mo, Cu, Cl, B. These are also called ‘Trace Elements’.

2.2 Sources of Essential Elements:–
Main sources are air and water. Carbon & oxygen are obtained from air. Hydrogen is obtained from water. C, H, O are the building blocks of macromolecules which form the plant body. Nitrogen is present in the air but plants cannot use it as such. So they get nitrogen from the soil as nitrates. P & S are also obtained from soil as Phosphates & Sulphates.

2.3 Role of Macro – and Micro nutrients:–
Essential elements perform many roles like:–
* Some synthesize components of the cell.
* Some take part in synthesis of materials
* Some act as components of enzymes * Some help in oxidation – reduction reactions
* Some participate in energy transfer, maintenance of osmotic pressure, buffer action etc.

HYDROPONICS:– It helps in determining the role of individual elements. It is a technique in which plants are grown with their roots immersed in nutrient solution without soil.
In this, plants are raised in small tanks covered with wire net. It is filled with water solution containing all the required elements. Solution is changed from time to time. Oxygen is bubbled in for proper aeration. For studying deficiency symptom, particular ion? is eliminated from the nutrient medium
Role of various elements are:–

1 - NITROGEN:–
Source:– Soil. It is absorbed as Nitrate, Nitrite or ammonium salts
Function:– It is required in greatest amount by plant. It forms proteins, vitamins, nucleic acids & hormones
Deficiency Symptoms:– Stunted growth, Yellowing of leaves, late flowering, purple shoot

2 - PHOSPHOROUS:–
Source:– Soil, in the form of phosphate ions
Function:– It is a constituent of cell membranes, proteins nucleic acids, nucleotides
Deficiency Symptoms:– Poor growth, delay in seed germination purple/red spots on leaves, premature falling of leaves

3 - POTASSIUM:–
Source:– Inorganic compounds like Potassium Sulphate (K₂SO₄), Potassium nitrate (KNO₃).
Function:– it helps to maintain anion – cation balance in cell, is involved in protein synthesis, opening – closing of stomata, activation of enzymes, maintaining turgidity of cells.
Deficiency Symptoms:– Scorched leaf tips, shorter internodes, premature death, bushy growth.

4 - CALCIUM:–
Source:– Soil, It is absorbed in the form of Ca²⁺ ions from CaCo₃ etc.
Function:– formation of mitotic spindle during cell division, for normal functioning of cell membranes, activation of enzymes, regulating metabolic activities.
Deficiency Symptoms:– Stunted growth, Necrosis, abnormal cell division.

5 - MAGNESIUM:–
Source:– Soil, absorbed as Mg²⁺ ion
Function:– Activation of enzyme in respiration & photosynthesis, synthesis of DNA & RNA, maintains ribosome structure
Deficiency Symptoms:– Chlorosis, Necrosis, Premature leaf abcission

6 - SULPHUR:–
Source:– Soil as sulphates (So₄^2–)
Function:– Forms aminoacids cysteine & methionine, constituent of coenzymes, vitamins
Deficiency Symptoms:– Chlorosis, stunted growth, anthocyanin accumulation, change in pigmientation

7 - IRON:–
Source:– Soil, It is obtained as Ferric ion (Fe³⁺)
Function:– It is important constituent of proteins like Ferredoxin. Takes part in electron transport, photosynthesis development of chloroplast
Deficiency Symptoms:– Chlorosis of leaves, reduced growth

8 - MANGANESE:–
Source:– from soil as Mn²⁺
Function:– Activation of enzymes involved in photosynthesis respiration and nitrogen metabolism
Deficiency Symptoms:– Chlorosis, grey spots on leaves, sterile flowers

9 - ZINC:–
Source:– obtained as Zn²⁺ ions from minerals containing zinc
Function:– Activation of enzymes, synthesis of Auxins
Deficiency Symptoms:– Distortion of leaves, reduction in fruits and leaves, smaller leaves

10 - COPPER:–
Source:– From soil as Cupric ion (Cu²⁺)
Function:– Overall metabolism of plant, chlorophyll synthesis
Deficiency symptoms:– Necrosis of leaf, dieback of shoot, rough bark

11 - BORON:–
Source:– From soil as BO₃^3–or B₄O₇^2–
Function:– Helps in uptake & utilization of Ca²⁺, membrane function pollen germination, cell elongation, cell differentiation.
Deficiency Symptoms:– Death of root/shoot tips, loss of apical dominance, small fruit size, stunted growth.

12 - MOLYBDENUM:–
Source:– Absorbed as molybdate ion (MoO₂²⁺)
Function:– Component of enzymes participating in Nitrogen metabolism
Deficiency Symptoms:– ‘Whiptail’ disease in cabbage where young leaves get distorted causes nitrogen deficiency

13 - CHLORINE:–
Source:– As chlorine gas or chlorides in soil
Function:– Cell division, in photosynthesis
Deficiency Symptoms:– Wilted leaves, stunted growth, reduced fruiting

2.4 Mechanism of Absorption of Elements:–
Plants absorb mineral ions from the soil through roots and then translocate these to other parts of the plant. In this process, two main phases are seen:–

1 - In first phase, ions are taken into ‘free space’ / ‘outer space’ of the cells. It includes intercellular space & cell wall. Here ions can be exchanged freely. Energy is not required in this process, so this is passive

2 - In second phase, ions are taken into ‘inner space’ which means cytoplasm & vacuoles. Here ions are not exchangeable. This process requires metabolic energy and so it is an active process.
Flux:– The movement of ions is called ‘Flux’
Influx:– Movement of ions into the cell is ‘Influx’
Efflux:– Outward movement of ions is ‘Efflux’.

Mineral absorption occurs by 2 methods –
Passive and Active

(A) Passive Absorption:– Energy is not required in this type of absorption. It occurs along concentration gradient for unchanged minerals (i.e, from higher concentration to lower concentration) and along electrochemical gradient for ions (as ions have charge also). Passageway is provided by membrane channels Various theories of passive absorption are:–

(i) Ion Exchange:– Exchange of ions takes place between roots and soil. Cations are exchanged with H⁺ ions Anions are exchanged with OH– or HCO₃^– ions. It can occur either bycarbonic acid exchange or by contact exchange. In carbonic acid exchange, CO₂ dissolves in H₂O to form H₂CO₃ which breakes up into H⁺ & HCO₃– . These can then be exchanged.
In contact exchange, ions present on the surface of roots come in contact with ions in the soil & get exchanged.

(ii) Donnan Equilibrium:– All cells have some fixed ions present on inner side which cannot diffuse out So, for reaching the equilibrium, additional ions (opposite in change to the ones fixed inside) are required. This continues till Donnan Equilibrium is reached when product of anions & cations in internal solution becomes equal to the product of anion & cations in external solution.          [ Ci⁺] [Ai^–] = [Co⁺] [Ao^–]
where            Ci⁺ = cations inside      Co⁺ = cations outside
A i ^– = Anions inside    Ao^– = Anions outside

(iii) Mass Flow Hypothesis:– According to this theory, ions are absorbed by the root along with mass flow of water under the influence of transpiration

(B) Active Absorption:– It is the absorption of mineral ions which involves the use of energy. The movement of ions is against concentration gradient. It occurs with the help of certain carriers present in the plasma membrane. Activated ions combine with these carrier proteins to form ion – carrier complex. This complex moves across the membrane & reaches inside where it breaks to release the ions into the cytoplasm. Ion Traffic Into the Root:–
Mineral ions are absorbed by roots and then carried to xylem. It occurs by two pathways:–
* Apoplastic:– Water & ions move through the cell walls without crossing any membrane and reach xylem.
* Symplastic:– Water & ions move across the cytoplasms of cell through plasmodesmata & reach xylem. So in this, they cross membranes & reach cytoplasm

2.5 Translocation of Solutes:–
Solutes move up in the plant along with the upward moving water. Water is moving up due to transpirational pull. So, the rate at which solutes are translocated corresponds to the rate of translocation of water.

2.6 Metabolism of Nitrogen:–
Nitrogen is absorbed in the form of nitrate (NO₃–) and ammonium (NH₄+) from the soil. It is essential for living organisms.

Nitrogen Cycle:– Atmospheric nitrogen is present in fixed forms as aminoacids, proteins, nucleic acids etc. in living organisms. When they die and decay, inorganic nitrogen is released. Dead remains decompose to produce ammonia. Ammonia converts into nitrites & then nitrates by process of Nitrification.
Bacteria Nitrosomonas converts ammonia to nitrate.
Bacteria Nitrobacter converts nitrite to nitrate.
Nitrate is then available to plant or gets converted into Nitrogen gas by process of Denitrification. Bacteria like Pseudomonas helps in this process.
Nitrogen gas may then be fixed again in the form of NH₄ by biological fixation

Biological Nitrogen Fixation:–
Nitrogen fixation done by microorganisms is called biological Nitrogen fixation. It is done by two ways:–
* By free living bacteria:– Free living N₂ – fixers include cyanobacteria, Azotobacter, Clostridium
* By Symbiotic bacteria:– Most common symbiotic bacteria is Rhizobium which lives in root nodules of leguminous plants. In symbiotic association, both the partners are mutually benefited. Nodules are the outgrowths of roots and act as site for N₂ – fixation. These contains enzyme – Nitrogenase (a Mo – Fe protein), pink colour pigment – Leghaemoglobin (which protects nitrogenase from oxygen) Formation of Root Nodules:– Root hair of a plant curls when it comes in contact with Rhizobium due to chemicals secreted by it. At the place of curling, bacteria invades root tissues and sometimes forms large structures called – Bacteroids. Cell walls of root hairs degrade and membrane forms infection thread by growing inwards Cell division in infected tissues continues and nodules are formed. Auxins (produced by plant cells) and cytokinins (produced by invading bacteria), together, promote cell division and formation of nodule.
N₂ – fixation is controlled by genes:– plant ‘nod’ genes, bacterial ‘nod’ genes, ‘nif’ & ‘fix’ gene clusters

Mechanism of N₂ fixation:– In N₂ fixation, atmospheric nitrogen gets reduced by addition of H – atoms. The three bonds (N º N) between two nitrogen atoms are broken. NH₃is formed which is used for the synthesis of amino acid.
N₂ fixation requires 3 components:–
(i) A strong reducing agent
(ii) ATP
(iii) Enzyme systems

Synthesis of Aminoacids:–
Aminoacids are initial products of nitrogen assimilation Each amino acid has an –NH₂ (amino) group and –COOH (carboxyl) group. Aminoacid synthesis occurs in following step:

(i) Reductive amination:– Amino acid reacts with  – ketoglutaric acid (comes from kreb’s cycle) and forms Glutamic acid.

(ii) Transamination:– In this, amino group from one amino acid is transferred to the keto group of keto acid 17 amino acids can be made from Glutamic acid by transamination. Enzyme acting is Transaminase

Amides:– eg, Asparagine, Glutamine. These are formed from aspartic acid and Glutamic acid when – OH part of acid is replaced by –NH₂. Enzymes
Glutamine synthetase or Asparagine synthetase help in the reaction Amides form proteins.

Protein Synthesis:– Many amino acids join to form a protein (or polypeptide). Peptide bonds join the amino acids or amides to form proteins.

2.7 Heterotrophic Nutrition:–
Organisms not capable of making their own food are called Heterotrophs. e.g, Phanerogams, fungi, bacteria etc. Heterotrophs can be:–

(a) Parasitic:– These obtain food from tissues of other plants. They have haustoria which penetrate into host plants vascular bundle and draws nutrition

(b) Saprophytic:– These grow on decaying animal or vegetable matter and absorb organic food from it eg Monotropa.

(c) Symbionts:– In this, two organisms live together and benefit each other mutually e.g, Lichen, mycorrhiza

(d) Insectivorous:– These plants obtain their food by catching insects and digesting them. Trapped insects are killed & their protein is digested byu proteolytic enzymes. Amino acids formed are absorbed by plant e.g, Drosera, Utricularia, Nepenthes.

PLANT - WATER REALTIONS

noreply@blogger.com (Unknown) — Tue, 20 Dec 2011 08:06:00 +0000

Cells are functional and structural units of all organisms. In plants, these cells have cell wall and protoplast. Each cell has its own internal environment. Plasmodesmata connect the protoplasm of adjacent cells.
Water is major raw material absorbed by plants and it is essential for all physiological activities of plants. Important roles of water in plant are: -

* It acts as solvent.

* Helps in uptake and distribution of solutes & minerals for plant growth.

* Has a key role in photosynthesis.

* Acts as source of oxygen

* WATER POTENTIALS: - Plants need free energy to grow and reproduce. Free energy is the potential to do work. The potential energy of water is known as'Water Potential'. Water moves from greater water potential area to lesser water potential. Water potential is measured in relative quantity. It is expressed as the difference between the potential of a solution in a given state and the potential of same solution in standard state.
Symbol: -It is represented by greek letter, Psi (ψ).
Unit: -Its measurement unit is'Pascal', Pa.
1 Mpa (1 Megapascal) = 10 bars.

Factors affecting water potential: -3 factors are there, which affect water potential
Amount of solute, pressure and gravity. So, water potential (w) of any solution is the sum total of these three potentials and can be represented as: -
_w =_S +_P +_g

WhereS ='Solute potential' or'Osmotic potential'; presence of solute particle decreases the water potential of pure water.
_P ='Pressure potential' or'Hydrostatic pressure'. If_P is positive, _w gets raised. If_P is negative. w gets reduced. Positive_P is called'Turgor pressure'.
_g ='Gravity potential'.It depends on height of water, density of water and acceleration due to gravity.
In plant cell,g is negligible. So, it is ignored. The equation, thus gets simplified as: - equation, thus
w =_S +_P.
According to this equation,
If water enters into cell, thep increases. Sow also increases. Thus difference between inside and outside. i.e. w is reduced.
If solute concentration increase thenS decreases. Sow also decreases. A water potential gradient develops and water enters into cell from outside.
Remember that water always moves from highw to low w.

1.2. Absorption & Movement of Water: -
Roots absorb water from the soil in plants. Root hairs present on the root increase the surface area for absorption. Water moves from root hairs to cortex and then to xylem. It moves by two pathways: -

* Apoplast pathway: - In this, water moves exclusively through cell wall. Cortex cells are loosely packed here, so water flows without any resistance till endodermis, where casparian strips block the flow. Major part of water flows via apoplast.

* Symplast pathway: -In this, water flows from cell to cell through plasmodesmata. So symplast has a network of cytoplasm of all cells interconnected by plasmodesmata. Beyond endodermis, water flows through cell membranes. This is called'Transmembrane Pathway' Water may also cross tonoplast.

DIFFUSION: -It is defined as the movement of molecules from the region of higher concentration to the region of lower concentration.
A state of equilibrium is reached when there is no further movement of molecules. In plants, uptake of water, gases and solutes occurs by diffusion.

PERMEABILITY: -The extent to which a membrane permits or restricts the movement of a substance is called Permeability.
It depends upon (i) Composition of membrane and (ii) Chemical nature of solute.
It can be measured by calculating the rate at which solute passes through membrane under specific conditions.

OSMOSIS: -The movement of water or solvent from a region of higher diffusion pressure to lower diffusion pressure through a semi-permeable membrane is called as'Osmosis'.

Demonstration of Osmosis by Thistle Funnel Experiment: -
Tie the mouth of thistle funnel with a semi permeable membrane (egg membrane). Put sugar solution inside it. Dip it in a beaker containing water with the help of stand. After some time, water rises in the thistle funnel. This is due to diffusion of water into thistle funnel through semipermeable membrane. i.e. by Osmosis.

Osmotic Pressure (O.P): -It is the external pressure which must be applied to stop entry of water/solvent due to osmosis.
O.P. is measured by instrument called'Osmometer'. Its unit is Pascal, Pa (1 Pa = 1 Newton/m²)

Osmotic Potential / Solvent Potential: -(_S)- It is defined as the amount by which water potential is reduced as a result of presence of solute. As chemical potential of water is taken as zero, so the value of solute potential always comes out to be negative.
_S = -
where - means negative of osmotic pressure.

Reverse Osmosis: -If more than required osmotic pressure is applied, then water flows out from the solution (in thistle funnel) back into the beaker (containing water). This is Reverse Osmosis. It is used for removing salts from saline water.

Factors affecting Osmosis: -
(i) Concentration of dissolved solutes in a solution
(ii) Pressure difference

Plasmolysis: -Shrinkage of the protoplast of a cell from its cell wall when it is placed in a hypertonic solution is called Plasmolysis.
Hypertonic solution has more solutes than solvent (water). So water moves out from cell. This causes shrinkage.

Imbibition: -It is the phenomenon of absorption of water or any other liquid without forming a solution. Material which absorbs water & swells up is called an Adsorbant. e.g Wood, Seeds, Agar-Agar. These are also known as'Imbibants'. Due to imbibition (water absorption), things swell up & lot of pressure is built. This is called Imbibition pressure / Matric Potential. ( water potential of matrix)
Conditions important for imbibition: -

* Water potential gradient between adsorbant and liquid.

* Affinity between adsorbant and imbibed liquid.

* Materials which have negative water potential allow rapid imbibition of water.

1.3 THEORIES OF WATER TRANSLOCATION: -
The movement of water from the roots to the tip of plant is called water Translocation.
There are 3 main theories for water translocation: -

* Root Pressure Theory: -given by Priestley (1916). Root pressure is the pressure developing in elements of xylem due to metabolic activities of root. Water is absorbed by root hairs from the soil. If a plant stem is cut just above soil, water oozes out of it. This is due to root pressure. Mineral ions from soil accumulate in xylem of roots and lower the osmotic potential which lowers the water potential. So water flows into the root.

* Capillarity Theory: -When water rises up in small tubes with small diameter which are kept in vessel filled with water, this is called'Capillarity'. Rise in water is due to forces of adhesion and cohesion. In this theory, first water is taken in because of adhesive forces (between water & xylem vessel walls). Then cohesive forces act between water molecules and so water moves up.

* Cohesion Theory: -Given by Henry Dixon in 1914. It is the most accepted theory. It states there is a continuous water column in plants because of cohesive forces between water molecules. When water evaporates from leaf, then the water potential decreases. Water from adjacent cells replaces the loss. Then water from xylem compensates this loss. So there is a continuous water column. The pull exerted on the water filled in xylem is known as'Transpiration Pull'. It results in upward movement of water.

1.4. Transpiration: -
Definition: -Loss of water, in the form of vapours, from the aerial parts of the plant is known as Transpiration. Most of the transpiration occurs through pores called'Stomata' present on the leaf.
Significance: -(i) It results in movement of water. Because when transpiration occurs water is absorbed from soil.
(ii) If extra water is absorbed, then transpiration removes it.
* It causes cooling effect on leaves (as transpiration involves evaporation which results in cooling).

* Increases the absorption of mineral nutrients.

Factors affecting Transpiration: -
* Humidity: -Rate of Transpiration is inversely proportional to relative humidity.

* Temperature: -Transpiration increases with increases in temperature. Higher temperature open the stomata. Lower temperatures close the stomata.

* Wind: -Transpiration increases with the wind speed (upto 20-30 km/hr) but if wind speed is too high, then stomata close and become dry. This decreases transpiration.

* Atmospheric Pressure: -Low atmospheric pressure increases rate of transpiration

* Light: -Stomata open in presence of light & close in darknes. So transpiration is more in light & lesser in darkness.

1.5. Opening & Closing of Stomata: -
Definition: -Stomata are tiny pores located on the surface of epidermal layers of leaves.
Size of stomatal pore: -3 - 12 mm wide, 10-14 mm long.
Number of pores: -1000-60,000 per cm² of leaf surface.
Location: -These occur on upper as well as lower surface of leaf. In monocots, their number is same on both the surfaces but in Dicots, these are more on lower surface.
Mechanism of opening and closing of stomata: -Each stomata has two guard cells surrounding the pore. These control opening and closing of stomata. When the guard cells are turgid (i.e. full of water), the stomatal pore opens. When guard cells are flaccid (i.e. have very less water), the pores close.
Guard cells take solutes from neighbouring epidermal & mesophyll cells. This lowers osmotic potential and water potential. It creates a gradient and water moves into guard cells which makes them turgid.Major solute taken in is k+ (potassium). Rise in k+ level causes stomatal opening. Decrease in k+ level closes the stomata.

Factors affecting stomatal movement: -
* Light: -Stomata generally open in light & close in dark.

* Temperature: - High temperature (above 35° C) can open stomata even in darkness. Lower temperature (less than 8° C) closes the stomata.

* Water: -If less water is available & transpiration is high, there is'water stress' or'water deficit' in plants. It closes stomata.

* pH: -High pH opens stomata. Low pH closes it

* CO₂: -Stomata close when concentration of CO₂ is high. These open when concentration of CO₂ is low.

Digestion and Absorption of Food

noreply@blogger.com (Unknown) — Mon, 28 Nov 2011 11:34:00 +0000

The gastrointestinal (GI) system includes the gastrointestinal tract (mouth, pharynx, oesophagus, stomach, small intestine, large intestine) and accessory organs (salivary gland, liver, gallbladder, pancreas) that secrete substances into the tract via connecting ducts.

GI system breaks down particles of ingested food into molecular forms by enzymes (digestion) that are then transferred to the internal environment (absorption).

Functions of GI organs

The GI tract begins at the mouth, where digestion begins with chewing. Saliva containing mucus and the enzyme amylase is secreted from 3 pairs of salivary glands, located in the head. Mucus moistens the food and amylase partially digests polysaccharides (starches). Food then reaches the stomach through the pharynx and ooesophagus.

The stomach is the sac that stores and digests food macromolecules into a solution called chyme. Glands lining the stomach secrete hydrochloric acid that dissolves food particles and protein-digesting enzymes, called pepsin.

Final stages of digestion and most of the nutrient absorption occurs in next portion of the tract: the small intestine. The small intestine is divided into 3 segments - duodenum, jejunum, and ileum.

The pancreas is a gland located behind the stomach. From its exocrine portion it secretes (1) digestive enzymes and (2) a fluid rich in HCO_3- ions to neutralize the acid from stomach. The liver secretes bile. Bile contains HCO_3- ions and bile salts to solubilise fats. Bile reaches the gall bladder through hepatic ducts and is stored in the gall bladder between meals. During a meal, bile is secreted from the gland by smooth muscle contraction and reaches the duodenum portion of the small intestine by the common bile duct.

Monosaccharide, amino acids and mineral salts are absorbed by transporter-mediated processes while fatty acid water diffuse passively.

Undigested material is passed to large intestine, where it is temporarily stored and concentrated by reabsorption of salts and water. Finally, contractions of rectum, the last part of large intestine, expel the faeces through the anus.

Structure of GI Tract Wall

The luminar surface is covered by a single layer of epithelium containing exocrine and endocrine cells. The exocrine cells disintegrate and discharge into the lumen, releasing their enzymes. The epithelia with an underlying layer of connective tissue (lamnia propia) and muscle (muscularis mucosa) are called mucosa. Below the mucosa is a layer of inner circular and outer longitudinal smooth muscle called muscularis externa, which provides the forces for moving and mixing the GI contents. The outermost layer of the tube is made up of connective tissue called serosa. The luminar surface of the tube is highly convoluted into projections called villi and microvilli; both of which increase total surface area for absorption. The center of each villus has a single blunt-ended lymphatic vessel called lacteal. Venous drainage from the intestine transports absorbed materials to the liver for processing via the hepatic portal vein.

Digestion and Absorption

Carbohydrate

Digestion begins in the mouth by salivary amylase and completed in the small intestine by pancreatic amylase. Monosaccharides, such as glucose, galactose and fructose, are produced by the breakdown of polysaccharides and are transported to the intestinal epithelium by facilitated diffusion or active transport. Facilitated diffusion moves the sugars to the bloodstream.

Protein

Proteins are broken down to peptide fragments by pepsin in the stomach, and by pancreatic trypsin and chemotrypsin in the small intestine. The fragments are then digested to free amino acids by carboxypeptidase from the pancreas and aminopeptidase from the intestinal epithelium. Free amino acids enter the epithelium by secondary active transport and leave it by facilitated diffusion. Small amounts of intact proteins can enter interstitial fluid by endo- and exocytosis.

Fat

Fat digestion occurs by pancreatic lipase in small intestine. A monoglyceride and two fatty acids are produced in the digestive process. Large lipid droplets are first broken down into smaller droplets, by a process called emulsification. Emulsification is driven by mechanical disruption (by contractile activity of GI tract) and emulsifying agents (amphipathic bile salts). Pancreatic colipase binds the water-soluble lipase to the lipid substrate.

Digested products and bile salts form amphipathic micelles. These micelles keep the insoluble products in soluble aggregates from which small amounts are released and absorbed by epithelial cells via diffusion. Free fatty acids and monoglycerides then recombine into triacylglycerols at the smooth ER, are processed further in the Golgi and enter the interstitial fluid as droplets called chylomicrons, which are then taken up by the lacteals in the intestine.

Vitamins

Fat-soluble vitamins are absorbed and stored along with fats. Most water-soluble vitamins are absorbed by diffusion or mediated transport. Vitamin B₁₂, because of its large size and charged nature, first binds to a protein, called intrinsic factor, which is secreted by the stomach epithelium, and is then absorbed by endocytosis.

Water

The stomach absorbs some water but most is absorbed at small intestine by diffusion.

Regulation of GI Processes

Control mechanisms of the GI system regulate conditions in the lumen of the tract. Reflexes are initiated by:

(1) Distension of wall by volume of luminal contents

(2) Chyme osmolarity

(3) Chyme pH

(4) Chyme concentrations of specific products.

Neural Regulation of the GI tract

Impulses to the GI muscles and exocrine glands are supplied by enteric nervous system, the local nervous system of GI tract, which allows local, short reflexes, independent of CNS. Long reflexes through the CNS are possible via sympathetic and parasympathetic nerves, which also innervate the GI tract.

Hormonal Regulation

Endocrine cells are scattered throughout GI epithelia and surface of these cells is exposed to the lumen. Chemical substances in the chyme stimulate them to release hormones into blood.

Phases of GI control

Each phase is named according to where the receptor for a reflex is located. These phases do not occur in temporal sequence.

1. The cephalic phase is initiated when sight, smell, taste, chewing, and emotional states stimulate receptors in the head. Reflexes mediated by sympathetic and parasympathetic fibers activate secretory and contractile activity.

2. The gastric phase is initiated by distension, acidity, and the presence of amino acids and peptides in the stomach. This phase is mediated by short and long reflexes and activates the secretion of gastrin.

3. The intestinal phase is initiated by distension, acidity, osmolarity of digestive products in intestine and is mediated by GI hormones and short and long neural reflexes.

Mouth, Pharynx, and Oesophagus

Chewing is controlled by somatic nerves to the skeletal muscles and the reflex activation of mechanoreceptors on the palate, gums and tongue.

Autonomic nerves in response to chemoreceptor’s and pressure receptors in mouth stimulate saliva secretion.

Swallowing is mediated by pressure receptors on walls of pharynx, which send impulses to the swallowing center in the medulla oblongata. The center activates muscles in the pharynx and oesophagus. Multiple responses occur in a temporal sequence. The palate is elevated to prevent food from entering the nasal cavity, respiration is inhibited and the epiglottis covers the glottis to prevent food from entering trachea (windpipe). The upper oesophageal sphincter opens and food enters the oesophagus and moves toward the stomach by muscle contractions called peristaltic waves. Food then moves to the stomach when the lower oesophageal sphincter opens. A less efficient, or faulty, lower oesophageal sphincter results in the reflux of gastric contents into the oesophagus (gastro-oesophageal reflux), this reversal results in heartburn and over time contributes to ulceration of oesophagus.

Epithelium lining the stomach invaginates into the mucosa, forming tubular glands. Parietal (oxyntic) cells secrete acid and intrinsic factor and chief cells secrete pepsinogen. Also scattered throughout are enterochromaffin-like (ECL) cells, which secrete histamine, and other cells that secrete somatostatin. The antrum, a lower portion of the stomach,secretes gastrin.

Increased protein content in a meal stimulates release of gastrin and histamine, which in turn stimulates HCl secretion. Somatostatin inhibits acid secretion by inhibiting the release of gastrin and histamine. Enterogastones in the duodenum also inhibit gastric acid secretion.

The precursor pepsinogen, which is produced by chief cells, is converted to pepsin by the acid in the stomach.

The stomach produces peristaltic waves in response to the arrival of food. The pyloric sphincter between the stomach and duodenum opens to release small amounts of chyme into the duodenum with each wave. These waves are generated by pacemaker cells in the longitudinal smooth muscle layer and are spread out by gap junctions. Gastrin, distension of stomach etc. stimulate gastric motility while distension of duodenum inhibits it.

Pancreatic Secretions

Inactive trypsinogen is secreted by pancreas and is later converted by the intestinal enzyme enterokinase to active trypsin, which digests proteins. Pancreatic amylase and lipase are secreted in active forms. The pancreas also secretes bicarbonate ions.

Secretion of pancreatic enzymes is stimulated by cholecystokinin (CCK), the secretion of which is triggered by the detected presence of fatty acids and amino acids in the small intestine. The secretion of bicarbonate ions is stimulated by secretin, which is triggered by acidity in small intestine.

Bile Secretion

Bile contains bile salts, which solubilize fats, and bicarbonate ions, which in turn are used to neutralize stomach acids. Bile salts, secreted by hepatocytes (liver cells) enter the GI tract and are reabsorbed by transporters in the intestine and are returned to the liver via the portal vein. This recycling pathway is called the entero-hepatic circulation.

The sphincter of Oddi controls the entry of the bile duct into the duodenum. When the sphincter is closed, secreted bile is shunted into the gallbladder. The presence of fat in the intestine releases CCK, which relaxes the sphincter to discharge bile salts into the duodenum.

Small Intestine

The most common motion of the small intestine is stationary contraction and relaxation, called segmentation. Segmentation results in little net movement. The chyme is mixed and brought into contact with the intestine wall and then moved slowly toward the large intestine. The movements are initiated by pacemaker cells in the smooth muscle layer.

After most of the materials are absorbed, segmentation is replaced by peristaltic activity called migrating motility complex, which moves any undigested material to the large intestine. The candidate intestinal hormone, motilin, initiates migrating motility.

Large Intestine

The large intestine consists of 3 parts: the cecum, colon and rectum. The primary function is to store and concentrate fecal material for elimination. Chyme enters the cecum through the ileocecal sphincter, which relaxes and opens as a result of the gastroileal reflex.

Na⁺ is absorbed along with water. K⁺ and HCO_3- ions are secreted into the lumen. Undigested polysaccharides (fiber) are metabolized to short-chain fatty acids by the residing bacteria and these are then absorbed by diffusion. A small amount of vitamin K is also produced and absorbed. Bacterial metabolism produces a mixture of gases, called flatus.

Motility and Defecation

Regular contractions of the circular smooth muscle produce a slow rhythmic segmentation movement. The undigested material moves slowly in order to provide resident bacteria time to grow and multiply. Following a meal, there is a wave of intense contraction, called mass movement. The internal anal sphincter is made of smooth muscle and closes the anus, while the external anal sphincter is made of skeletal muscle and is under voluntary control. Both sphincters regulate the anal opening and closing. Mass movement of fecal material into the anus initiates the defecation reflex, which is mediated by mechanoreceptors. The two sphincters open to expel the feces. If defecation is delayed, rectal contents are driven back into colon by reverse peristalsis until the next mass movement.

Pathophysiology of the GI Tract Ulcers

Ulcers are eroded areas of gastric surface and breaks in the mucosal barrier, which expose the underlying tissue to corrosive action of acid and pepsin. Damage to underlying blood vessels may cause bleeding.

Vomiting

The vomit reflex results in the forceful expulsion of toxic gastric contents. This reflex is coordinated by the vomiting center in the medulla oblongata. Various mechano- and chemo- receptors in the stomach and elsewhere can trigger this reflex. Increased salivation, sweating, heart rate, pallor etc. accompany the reflex. Abdominal muscles contract to raise abdominal pressure while the lower esophageal sphincter opens and gastric contents are forced into the oesophagus (retching). If the upper esophageal sphincter opens, contents are then expelled from the mouth (vomiting). Excessive vomiting can lead to loss of water and salts, which will ultimately result in dehydration.

Gallstones

Excessive secretion of water insoluble cholesterol in bile results in formation of crystals, called gallstones, which can close the opening of gallbladder or the bile duct. If a stone prevents bile from entering the intestine fat digestion and absorption decreases. If a stone blocks the entry of the pancreatic duct, it prevents pancreatic enzymes from entering the intestine, thus preventing the digestion of other nutrients. A blocked bile duct inhibits further secretion of bile, resulting in accumulation of bilirubin in tissues, producing a yellowish coloration called jaundice. Jaundice is common in newborns and is rectified by sunlight exposure.

Lactose Intolerance

Lactose intolerance results from a lack of the enzyme lactase which digests lactose, the sugar in milk. The lack of lactase results in the incomplete digestion of lactose to glucose and galactose.

Constipation and Diarrhea

Constipation is the absence of defecation due to decreased motility of the large intestine. This results in excess absorption of water from feces, making it hard to expel.

Dietary fiber, which is not digested in small intestine, can produce distension and increase motility.

Diarrhea results from decreased fluid absorption, or increased fluid secretion resulting in increased luminal fluid, which in turn, causes distension and increased motility. Diarrhea results in decreased blood volume, loss of water and other nutrients.

The Human Digestive System

Digestion is the breaking down of chemicals in the body to a form that can be absorbed and used. Digestion begins, in mammals, with the saliva in the mouth.

The Mouth

This is the buccal cavity in a human and is where mechanical digestion and mastication (chewing) takes place.

Saliva in the mouth consists of mucin (binds food together), salivary amylase (digests starch to maltose) and mineral salts (regulates pH around 7, neutral).

Oesophagus

Peristalsis of the circular muscle contracts and relaxes to push food down.The upper part of the ooesophagus is under conscious control until a point when it becomes involuntary.It usually takes between 4 and 8 seconds for food to travel from mouth to stomach.

Stomach

Acidic conditions (pH1/2, enzyme optimum pH). Mechanical digestion takes place here (churning of the stomach makes food break down in size giving it a larger surface area).While food is in the stomach it mixes with gastric juice by churning. Food in the stomach stimulates stomach wall to produce gastrin (transported in the blood).With a fatty meal enterogasterone is produced to slow churning, it also weakens the acidic pH of the stomach.

The gastric juices produced consist of:

Pepsinogen – made inactive to prevent autolysis and when added to HCl become active and is then called pepsin and is used to convert proteins.

Pro-rennin – when added to HCl forms rennin used to coagulate caseinogen and increasing surface area allowing a chance to digest.

Hydrochloric acid (HCl)

Mucus

Pro-rennin is only found in babies though, used for the digestion of the mothers milk.

Mucus is used for the protection from excess stomach acid and most of all autolysis. It also acts as a lubricant, reducing friction.

The stomach wall contains oxyntic cells which secrete hydrochloric acid (HCl), goblet cells which secrete mucus and peptic cells which secrete pepsin.

Chyme is the word we use to describe the semi-liquid food which is now all mixed together.

Duodenum (early small intestine)

This is the first 20cm of small intestine and receives secretions from the liver and pancreas.

Further digestion takes place.

Input of pancreatic juices.

Lipids broken down into fatty acids.

Protein broken down into amino acids.

Large surface area due to a large number of villi (villus).

The digestion of carbohydrates takes place inside cells.

Liver

Produces bile (stored in gall bladder, transported by the bile duct).

Bile made from bile salts and mineral salts.

Bile salts help with the digestion of fats by breaking them down from large globules to smaller globules, lowering surface tension and making a larger surface area.

Mineral salts neutralise the stomach acid (HCl) to around 7/8 pH in the small intestine.

Pancreas

Produces pancreatic juices which contain pancreatic amylase, pancreatic lipase and trypsinogen (or trypsin in its active form).

Pancreatic amylase converts the remaining amylose (starch) into maltose.

Pancreatic lipase converts lipids into fatty acids and glycerol

Trypsinogen, upon meeting with the enzyme enterokinase, is activated and is called trypsin. Trypsin then continues to break down proteins in digestion.

Brunner’s gland

Located in the wall of the duodenum.

Secretes alkaline juices (which help maintain the correct pH) and mucus (for lubrication and protection).

Ileum

· This is the longest part of the small intestine.

· Secretes endopeptidases and exopeptidases.

· Endopeptidases break proteins into small polypeptides by breaking the bonds in the middle.

· Exopeptidases also break down protein but by taking single amino acids of the end. Both work together to break down the proteins into small amino acids.

· Sucrose is hydrolysed into fructose and glucose by sucrase.

· Maltose is also hydrolysed into two glucose by maltase.

· Contains crypts of Lieberkuhn which secrete maltase, sucrase, endopeptidases and exopeptidases.

Small Intestine in General

Glucose and amino acids are absorbed over the epithelium of the villi by diffusion and active transport into the capillaries of the villi.Once absorbed from the small intestine and into the capillaries, the products travel through the venules and the hepatic portal vein into the liver. Here in the liver toxins like alcohol, drugs, spent hormones and other toxins get converted into a non-toxic form. When they’re safe and non-toxic they can be transported to the kidney in the form of urea.

The absorption of fatty acids and glycerol don’t enter straight into the capillaries instead entering the lacteal of the villi and then into the lymphatic system and then via the thoracic duct into the blood system.

Products from digestion do one of three things, they either get stored (assimilation), used or converted (deamination). An example of assimilation is excess glucose being stored in the liver as glycogen. Deamination only occurs with excess of amino acids, they then get converted into urea by the removal of the amino group (NH₂) which combines with CO₂ to form CONH₂ (urea). The remaining organic molecule can be broken down and respired.

The final products of digestion, carbohydrates in the form of monosaccharides, proteins in the form of amino acids and lipids in the form of fatty acids and glycerol.

Large Intestine

The large intestine absorbs water (by osmosis), minerals and vitamins.

Chyme at the start of the large intestine consists of water, bile, mucus, dead cells, bacteria and undigested food.

The large intestine has a larger lumen, is smaller in length and has a thinner wall than the small intestine.

**Faeces is stored in the rectum and then egested through the sphincter muscle called the anus.

**Diarrhoea causes dehydration because of the lack of absorption. Pernicious Anemia is another disease and is caused by not absorbing enough vitamin B and can be a side effect of diarrhoea.