Science General Zoology

Phylum Porifera

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This phylum includes the sponges; the lowly multi-cellular animals incapable of movement and resembling plants. The different species may be thin flat crusts, vaselike, branched globular or varied in form. Most of the Porifera are Marine and all are sessile. They are attached to rocks, shells and other solid objects in the water. The name Porifera refers to the porous structure of the body. Some or all inferior surfaces are lined with choanocytes or flagellated collar cells.

The sponges have an internal skeleton of separate crystalline spicules or of irregular sponging fibers or both. They reproduce sexually or asexually by buds or gemmules. The representatives of this phylum include Scypha, Euplectella aspergillum (Venus flower basket), and Euspongia (Bath sponges).

Scypha - This is formerly called Scycon or Grantia. The Scypha is slender form rarely over 2.5 (cm) centimeters tall, with one tubular central cavity and a single osculum, and with a large opening at the summit. The thick body wall is folded to form many short horizontal canals. The incurrent canals open from the exterior through small pores but end blindly toward the inner surface, whereas the radial canals begin blindly near the outer surface and open by minute apopyles into the spongocoel, the central cavity. The radial canals are lined with choanocytes or flagellated collar cells.

Phylum Protozoa

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Protozoans are mostly one-celled animal-like protistans of microscopic size. The cell form is usually constant, oval, elongate, spherical, or otherwise varied in some species and may change with the environment or age in many. Specialized structures termed organelles may be found in their body; “organs” or “tissues” are not relevant terms for them. The nucleus may be single or multiple. Locomotor organelles may be either, flagella, cilia, pseudopodia, etc. Many are free-living others sessile; some form colonies. They reproduce asexually by fission, budding and cyst formation; sexually by conjugation of gametes. Common representatives of this phylum are the Amoeba, Euglena, Paramecium.

Amoeba- It looks transparent or translucent jelly like object that hardly move at all. It is in constant motion, putting out tiny projections, the pseudopodia or false feet. It has thin delicate outer membrane, the plasmalemma. Beneath this is a non-granular layer, the ectoplasma which encloses the granular endoplasma. Watch the non-moving part of the endoplasm a large, clear, spherical contractile vacuoles. The nucleus is rounded, finely granular and very refractive body in the neighborhood of the contractile vacuole.

Paramecium- In the same protozoan culture, for rapidly moving, relatively large, almost microscopic slipper-like animals more or less yellowish in color. The small rounded end is the anterior end; the large pointed end is the posterior end. At one side of the body is a concave depression, the oral groove. The side on which this is located is the ventral or oral side; the opposite is the dorsal or aboral side.

The shape of the animal is maintained to a thin membrane, the pellicle or cuticle. From all over the cuticle numerous short oar-like hairy projections are found, the cilia, the organelles of locomotion. Beneath the cuticle is a dense protoplasmic region, the ectoplasm which surrounds the larger mass of granular endoplasm. Embedded in the ectoplasm are spindle-shaped cavities known as trichocysts, filled with a semi-fluid substance that may be discharged as long threads for attachment and defense. The trichocysts alternate with the bases of the cilia.

At the posterior end of the oral groove is the mouth (cytostome) which leads into the tubular gullet or cytopharynx. Along the gullet are two rows of fused cilia, the undulating membrane.

Euglena- It is a protozoan that moves about by means of a whip-like organelle called flagellum. Many of them possess chlorophyll, the green pigment that allows them to manufacture their own food from water and carbon dioxide with the help of sunlight. Euglena is narrow and elongated. It can contract and twist its body into a sphere, a type of movement oftentimes called euglenoid movement.

Taxonomic Survey of the Animal Kingdom

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There are many kinds of animals existing on earth and several of them have lived the past geologic time. These animals need to be grouped and named in order to be able to intelligently communicate about them. Animal taxonomy or systematic zoology deals with classification, the arrangement of the kinds of animals in the hierarchy of small and large groups and nomenclature, the procedure of assigning names to the kinds and groups of animals to be classified.

The animal kingdom is generally divided into a number of phyla which are split into classes, the classes into orders, the orders into families, families into genera, and general into species. Intermediate categories (subfamilies, superclasses, subphyla, etc.) are sometimes needed in advanced classifications to indicate fine degrees of relationship.

Under the Linnean or binomial system of nomenclature, an animal is assigned a scientific name. The name consists generally of a generic name (genus), which is written with a capital initial letter and a specific name (species) which is written with a small initial letter. A third name (subspecies) is sometimes applied to designate the race of the species, i.e., the name is trinomial. The scientific name of the common rice field frog for example is Rana limnocharis vittigera, while that of modern man is Homo sapiens.

There are more than a dozen phyla in the animal kingdom, however, only the ten major ones will be considered in the present study, namely, Protozoa, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Mollusca, Chordata, Arthropoda, and Echinodermata.

Classification of the Frog

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The frog may be classified in below-stated categories. The distinct characteristics of the frog are the following:

Phylum Chordata – The animal has notochord (this is present only during the embryonic or larval stage), gill slits at the pharyngeal wall, and a tubular system dorsal to the digestive tract.
Subphylum Vertebrata – This chordate has an axial support of vertebral column which replaces the notochord is later development.
Class Amphibia – This vertebrate can live both in water and on land.
Order Anura or Salientia – This kind of amphibian has no tail in the adult stage although this was present on them during the larval stage. The body is short and compact; the posterior limbs are longer and stronger that the anterior limb. These are used by them for jumping.
Family Ranidae – This anuran has soft, non-poisonous, slimmy skin unlike the toad which has warty and poisonous skin.

The most common frog species used in the laboratory is the rice field frog, the Rana Limnocharis Vittigera.

Animal External Anatomy

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Preserved Frog Examination

Get a preserved frog and put, and study it’s external characteristics. The body is divided into two general regions, the axial and the appendicular. The axial region consists of the head and the trunk, while the appendicular region consists of the limbs. The head is fattened; the trunk is elongated and slightly cylindrical. The frog has no neck and tail although the tail is present in the larval or tadpole stage and is used for swimming.

In the head region; the more or less triangular border at its end is the snout. It bears two small openings at the tip, the nostrils or external nares. Behind the nares are the eyes containing a curtain-like structure, the iris which has a central opening that appears black; the pupils. The eyeball is a thin semi-triangular membrane, the nictitating membrane or third eyelid which is an outgrowth of the lower eyelid.

Posterior to the eye is a circular area of thin membrane, the tympanic membrane which is quite distinct from the skin. Internal to this membrane is the middle ear which contains a bone, the Columella.

At the dorsal median portion of the head just in front of the level of the eyes is the browspot. This is believed to be the remnant of a third eye.

The anterior opening of the digestive tract, the mouth is found at the tip of the head, bordered by the snout. The posterior opening, the anus is the opposite end of the body just between the point of origin of the legs. Notice the dorsal elevated region of the trunk, the hump, which is typical of frogs.

In the appendicular parts, the short forelimb or the anterior extremity has three divisions: a proximal upper arm, a middle forearm and a distal manus or hand. In the skin of the inner side of the hand for the rudiment of a missing finger which corresponds to the thumb of man. The long hind limb or posterior extremity is also divided into three parts, the thigh, shank, and pes or foot. Count the number of toes the frog has. The inner side of the foot has a rudiment of a missing toe, the prehallux or calcar which may be felt near the hallux. The hallux corresponds to the big toe of man. Notice the membranous extension of skin, the web connecting a great part of the length of the toes and which functions for swimming.

How to determine whether your frog is a male or female? The male from is smaller and has dark pigmented areas at the posterior angle of the ventral side of the head. During the breeding season, the thumbs are more swollen in the male than in the female.

Gross Morphology

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Anatomical Study of Animals Terminology

The following terms are used in the anatomical study of animals:

Cephalic – This is the part of the body lying toward the head. (In most animals this is the anterior end, but in man this is the superior end).

Caudal – This is the part of the body lying toward tail or posterior end of most animals. (In man this is the inferior end).

Dorsal – This is any part of the body lying on the upper part or back of the animal.

Ventral – This is any part of the body lying on the belly or underside of the body.

Lateral – This is any part of the body lying toward or beyond the side of the body.

Mesal – This is any part of the body lying toward the median plane.

Proximal – This is the part of the appendage near the main mass of the body.

Distal – This is the part of the appendage away from the main mass of the body

Ectal or Superficial – This is the part near the external surface of the body.

Ental or Deep – This is the part near or at the center of the body.

Imaginary Planes and Axes as Structural Reference

The following imaginary planes and axes serve as structural reference:

Median Plane – This is a vertical longitudinal plane passing from head to tail through the center of the body from dorsal to ventral surfaces. It divides the body into two identical right and left.

Sagittal Plane – This is any vertical longitudinal plane through the body. It may be the median sagittal plane, if it passes through the median plane or parasagittal if it is a sagittal plane other than the median plane.

Horizontal or Frontal Plane - This is any plane at right angle to the median plane and parallel to the dorsal and ventral surfaces.

Transverse Plane – This is any plane that cuts vertically across the body at right angle to the sagittal and horizontal planes.

Longitudinal or Anteroposterior Axis – This is a line in the median sagittal plane extending from head to tail.

Sagittal or Dorsoventral Axis – This is any line in the median sagittal plane extending from dorsal to ventral surfaces.

Transverse or Mediolateral Axis – This is any line in the transverse plane running from side to side.

Ovary

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It is attached to the dorsal body wall by a double-layered membrane, the Mesovarium.

This membrane continues around the entire ovary as the Theca Externa.

Suspended within the theca externa are numerous individual sacs, each made up of another membrane, the theca interna or cyst wall which contains smooth muscle fibers.

The theca interna surrounds each egg except for the limited area bulging toward the body cavity where it is covered by the theca externa only.

For a cluster of Oogonia, small immature egg cell, and the Oocytes, the bigger, more mature egg cells.

The theca interna plus limited covering of the theca externa and the follicle cells together comprises the Ovarian Follicle.

Within each follicle are found Follicle Cells, with their oval and granular nuclei.

The follicle cells surround the developing egg and are found in close association with it throughout those processes of maturations which occur with the follicle.

Enclosed within the follicle cells and closely applied to each mature egg is the non-cellular and transparent Vitelline Membrane.

Liver

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The liver cells which constitute the bulk of the organ are polygonal in shape and contain deeply stained nuclei.

The tissue cells are clustered with spaces in between called Sinusoids.

Arranged in circles of five and six cells in cross section are the large cuboidal cells of the Bile Capillaries.

Those lined with more than six cells are the Bile Ducts.

For large blood vessels and small blood capillaries; they contain blood corpuscles in their lumen.

Scattered in the liver are pigment granules that give color in the organ.

Stomach

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The general appearance and arrangement of the layers are the same as in the intestine. However, the Tunica Mucosa and Tunica Muscularis are much thicker, whereas Gastric Glands instead of Goblet Cells are found in the tunica muscosa.

The tunica muscularis is composed of a circular layer only. The outer layer known as the Subserosa, consists mostly of connective tissue with only a few longitudinal muscle fibers. Between the mucosa and the submucosa lies a thin layer, the muscularis mucosa which is not found in the intestine. It is made up of two layers: an inner layer of circular muscle fibers and an outer layer of longitudinal muscle fibers.

The big folds at the inner portion of the stomach are called Rugae; they serve to increase its surface are. Within the folds are several tubular depressions, the gastric glands which are lined by epithelial cells.

Intestine

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Starting from the outside going to the innermost portion are the following layers.

The Tunica Serosa or Visceral Peritoneum is a thin coat of peritoneum that lines and protects the outer surface of the intestine.

The bulk of the wall of the intestine is formed by the Tunica Muscularis which contains two sublayers, the outer thin Longitudinal Muscle Layer and the Circular Muscle Layer.

They are so named because of the direction along which the muscle fibers run.

The Tela Submucosa is a layer made up of connective tissue with blood vessels and lymph spaces.

The innermost layer, the tunica mucosa is the epithelial layer thrown into folds, the villi, which are filled in life with mucus. Hence, it’s the name of the layer.

Artery and Vein

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Obtain a slide containing sections of an artery and a vein.

Both are made up of three coats or layers: an outer Tunica Externa, composed mostly of connective tissue, a middle tunica media, composed of connective tissue and muscle; and an Inner Tunica Interna, composed of connective tissue and endothelial lining.

The connective tissue components enable the vessels to withstand pressure; the muscle regulates the amount of blood delivered to an organ; and the endothelium affords a smooth surface for the lumen in which the blood flows. Observe the difference in the thickness of the different layers between artery and vein.

Testis

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The Testis

Testis

It is covered by a membrane, the Tunica Albuginea and is suspended from the dorsal body wall by a mesentery, the Mesorchium. Observe the numerous subdivisions of the testis, the Seminiferous Tubules. These are closely packed, oval shaped sacs separated from each other by thin partitions of connective tissue known as Intestinal Tissue.

Sperm cells undergoing the process of Spermatogenesis can be seen. Each seminiferous tubule may contain all the stages of maturing sperm cells. Each stage is found in a cluster or group within the tubule and is enclosed by another thin membrane forming a Spermatocysts.

The Spermatogonia have lightly stained nuclei showing dot-like portions of Chromatin; they are found near the periphery of the tubule.

The larger primary Spermatocytes which are in various stages of meiotic prophase have lightly and darkly stained nuclei. The smaller secondary spermatocytes which are undergoing different stages of mitosis have darkly stained nuclei with distinct highly contracted chromosomes. The Spermatids which are in the process of Metamorphosis have different shapes. Some are small darkly spherical bodies; others are dark elongated structures preparatory to the formation of the tail or Flagellum. The Spermatozoa or the mature sperm cells appear as masses of hair-like structures in the lumen of the tubule or attached to Sertoli Cells. The sertoli cells which provides nourishment to the spermatozoa is an elongated, somewhat triangular cells with its base attached to the basement membrane of the tubule. The residual spermatogonia, surrounded by Follicle Cell, may be seen at the periophery of the tubules; they are few large vacuolated cells with distinct nucleus.

Spinal Cord

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The Spinal Cord

Spinal Cord

The cord is enveloped in a thin membrane, the Dura Meter, below which is the Subdural Space. Under this and in close contact with the spinal cord proper is another membrane, the Pia Meter. The entire mass of the spinal cord can be differentiated into an inner portion or central part, the Gray Matter, and an outer or peripheral part, the White Matter. The cavity at the center of the spinal cord is the Central Canal. On the mid-dorsal side of the spinal cord is the Dorsal Fissure. It is narrow and shallow and continues toward the central canal by a narrow Dorsal Septum. On the ventral side is the Ventral Fissure. This is deeper and wider and it extends almost to the central canal. It encloses a small artery, the ventral spinal artery.

It is mostly made up of bodies of Nerve Cells or Neurons and of supporting cells, the Neuroglia Cells. The four corner of the gray matter is thrown into processes, the Horns and Cornua. The Ventral Gray Horns and broader than the dorsal; they contain the big Motor Cells. These cells have prominent nuclei with distinct nucleolus.

It consists mainly of nerve fibers that take their origin from the neurons of the gray matter. The white matter also contains supporting cells, the neuroglia cells which form a sort of supporting tissue for the other elements of the nervous system.

Vascular Tissue

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The Vascular Tissues

Vascular Tissues

The blood and lymph that serve to transport and distribute materials in the body consist of fluid plasma containing free cells or corpuscles. Colorless white blood cells or leukocytes are present in both man and frog. The red blood cells or erythrocytes are colored red by a pigment, hemoglobin that serves for the transport of oxygen.

Human erythrocytes are non-nucleated, biconcave and usually round. In the frog, they are nucleated, biconvex and oval.

Look for leukocytes in the human blood. They are few in number, bigger and have darker color than the erythrocytes. They are classified into granulocytes, with granules in the cytoplasm and agranulocytes without cytoplasmic granules.

The granulocytes or polymorphonuclear leukocytes are the neutrophils, eosinophils and basophils. They differ in the shape of their nuclei and the size of their cytoplasmic granules. The neutrophils have three or more lobules in the nucleus which are joined by thread-like structure; they have very fine cytoplasmic granules. The basophils have non-lobulated twisted nucleus and have fewer granules in the cytoplasm. The eosinophils have two lobules in the nucleus and larger cytoplasmic granules.

The agranulocytes are the monocytes and lymphocytes. The lymphocyte is small with a big nucleus occupying almost the entire cell. The monocytes are big with bean-shaped nucleus.

Kidney

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The Kidney

Kidney Anatomy

Kidney

The dorsal part is rounded while the ventral part is flattened or slightly concave. Attached to the median ventral border is a small mass of epithelial cells, the adrenal gland. There is the Renal Portal Vein and the Mesonephric Duct. The former can be identified by the presence of blood corpuscles in the lumen whereas the latter can be identified by the presence of Cuboidal Cells lining the lumen.

The Kidney proper is made up of the mass of intricately coiled and twisted tubules, the Uriniferous Tubules. These tubules may appear as small circles or narrow cylinders in cross section. Its wall is made up of single layer of cuboidal epithelial cells surrounding a central narrow lumen.

The numerous prominent rounded masses each mass being called Malpighian Body or Renal Corpuscle. It is made up of centrally located network of blood capillaries, the Glomerulus around which is a delicate, thin cup-shaped double membrane, the Bowman’s Capsule. At one end it is connected with the uriniferous tubule, but at the other end it is open. Through this opening blood vessels connect with the capillaries of the glomerulus. Waste materials removed from the blood pass through the glomerulus. Then these materials diffuse to the Bowman’s capsule from where they go to the uriniferous tubules, to the mesonephric duct and finally to the cloaca and anus.

Organology

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The Organology

The Skin

Organology

An organ is a group of tissues performing a definite function. The component tissue of the skin, blood vessels, digestive tube, various glands and the spinal cord will be described.

The Skin

The skin is composed of more than one layer of epithelial cells. The outermost layer is the Stratum Corneum, which is composed of flat, thin cornified cells that are constantly shed by the frog. They are the same cells that were studied as squamous epithelial cells. Below the stratum corneum is the Stratum Germinativum, which is made up of several columnar cells of various thicknesses. They frequently contain granules of brownish pigments or Chromatophores.

The Dermis is divided into an outer layer, the Stratum Laxum or Stratum Spongiosum, and an inner layer, the Stratum Compactum. The connective tissue fibers of this layer are loosely aggregated and in life contain large amount of lymph and blood. This layer also contains numerous pigment cells and bodies of bulb-like glands, the Cutaneous Glands. These are simple glands produced by the infolding of the stratum germinativum. Some of the glands show their opening to the outside. The inner bulb-like body is connected to the mouth by means of a narrow neck.

There are two kinds of cutaneous glands, the Mucus and the Poison Glands. The mucus glands are smaller and much more numerous that the poison glands. Poison glands are fewer and may not be present in your slide.

The stratum compactum is a layer that appears as a solid heavy mass of connective tissue fibers running more or less parallel to the surface of the skin. At certain regions, vertical strands cut at right angles the wavy horizontal layers. These strands are made up of connective tissue fibers with blood capillaries, nerve cells and few muscle fibers.

Beneath the stratum compactum is the region composed of loosely arranged connective tissue fibers which forms the boundary between the skin and the muscles.

Nervous Tissue

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The Nervous Tissue

Nervous Tissue

Nervous issues are composed of nerve cells or neurons. The individual neuron has a large cell body, wherein the nucleus is located and nerve fiber or processes which carry impulses to and from the body. The process that transmits stimuli to the cell body is the dendrite and that carrying impulses away from it is the axon. The nerve cell bodies form the gray matter of the central nervous system or they may aggregate outside into ganglia. The nerve fibers constitute the white matter of the central nervous system or they may form bundles the nerves.

A nerve cell consists of a transparent central portion, the axis cylinder and an outer sheath of fatty substance, the medullary sheath or Schwann cells. The medullary sheath is covered by a thin membrane, the Neurilemma or Sheath of Schwann: at intervals, the medullary sheath is discontinuous, forming the nodes of Ranvier. Each intermodal segment bears oblique markings on the medullary sheath, the incisures of Schmidt.

The nerve bundles or fascicles joined together by connective tissue. Two or three fascicles are bounded together by a connective tissue, the epineurium which extends inward to enclose each bundle forming the perineurium or to pass inward between nerve fibers as the endoneurium. The nerve fibers are the tiny rounded structures inside each fascicle.

Muscular Tissue

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The Muscular Tissue

Muscular Tissue

The movement in most animals is produced by long slender muscle cells. These contain minute fibers or myofibrils which contract upon stimulation. There are three types of muscles in vertebrates: Skeletal or striated voluntary muscle; smooth or unstriated involuntary muscle, and cardiac or striated involuntary muscle.

The cells or muscular tissues contract and relax, thus creating mechanical energy required for movement of the body and its parts. Muscle cells are arranged in group as fibers, embodied in the surrounding connective tissue to which they are bound by intercellular substance.

There are three (3) kinds of muscular tissues:

Smooth Muscle Tissue
Striated Muscle Tissue
Cardiac Muscle Tissue or Heart Muscle Tissue

Smooth or Unstriated Involuntary Muscle

The muscle layer consists of spindle-shaped cells each with a nucleus at the center. The cytoplasm is called sarcoplasm, the cell membrane, sarcolemma.

This consists of long cells in sheets, layers or bundles, and cytoplasm of each cell contains the contractile elements, or myofibrils; it is found in the wall of the digestive tract, walls of blood vessels, the urinary bladder and gallbladder, the genital ducts, the bronchi and trachea, and the iris. Its action is involuntary.

Skeletal or Striated Voluntary Muscle

The muscle fibers are long with alternating dark and light bands giving the striated appearances to the muscle. Each fiber is provided with numerous nuclei scattered in the cytoplasm. This condition is called syncytium.

This consists of bundles of fibers made up of large nucleated cells with myofibrils that have alternating dark and light bands, giving, the fibers a striped appearance. It is found in skeletal muscles, muscles of the tongue and soft palate, the scalp, the pharynx, the upper esophagus, and the eye. In most cases its action in voluntary.

Cardiac or Striated Involuntary Muscle

The cardiac muscle has delicate cross striations; the fibers are branched forming an interconnecting network.

This consists of a network of branching fibers connected to adjoining fibers, having striated cells and transverse markings called intercalated discs. Its action is involuntary, automatic, and rhythmic. Within the heart too, are special muscle fibers, the Purkinje fibers which have fainter striations, fewer myofibrils, and more intercellular material than the typical heart muscles. They constitute the impulse-conducting system of the heart.

Connective Tissues

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The Connective Tissues

Connective Tissues

This tissue supports, binds, and connects together the different parts of the body. It differs from other tissues in having a great amount of intercellular substances modified into different forms. They are classified into fibrous, adipose, cartilage and bone.

Fibrous Connective Tissue

This is the membrane connecting the skin with the underlying muscles. The matrix is a gelatinous amorphous ground substance in which are embedded white or collagenous fibers and yellow or elastic fibers. The white fiber are made up of many fine parallel fibrils, pale in color and often wavy in outline forming bundles that criss-crossed or interlaced. Elastic fibers are sharply defined, few, straight and frequently branched.

Adipose or Flat Tissue

This consists of cells that are rounded or polygonal with thin layers of cytoplasm and the nucleus at one side. They contain droplets of fat which may form large globules. Fat is usually dissolved out in prepared microscopic sections leaving only a framework of cell outlines.

Cartilage

The clear hyaline portion is the matrix or intercellular substance which is secreted by the cartilage cells or chondrocytes. These cells are scattered irregularly and located in rounded spaces or lacunas. Empty lacunae may also be found.

Bone

Bone is dense organic matrix with mineral deposits. The bony substance or bone matrix is arranged in regular concentric layers or lamellae. Within the bone matrix are scattered numerous minute spaces or lacunae in which the bone cells or osteocytes are located in life. Arising from the lacunae are numerous thin branching canals, the canaliculi which lead to neighboring lacunae, thus establishing connections among them. The central cavity where blood vessels pass and into which the canaliculi from the innermost row open directly is the haversian canal. The concentric lamellae with their lacunae and canaliculi together with a haversian canal constitute a haversian canal system.

Histology

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What is Histology

Histology of Animal Cell

Histology

A group of cells of similar structure and function is called a tissue. The study of tissues is called histology. The cells in the multicellular animals may be divided into: 1) somatic cell or body cells consisting the individual animal throughout its life; and 2) germ cells or sex cells, having to do with the reproduction of the species. The somatic tissue may be any of the following kinds: a) epithelial, b) connective, c) vascular, d) muscular, and d) nervous.

Epithelial Tissues

These tissues cove the outer and inner surfaces of the body as in the skin lining of the digestive system, lining of the glands, blood vessels, mouth, nose and anus. The cells are compactly clustered, bonded together by intercellular cement for strength and often supported below by a basement membrane. Epithelial tissues are of different kinds depending on the shape of their component cells as follows:

Squamous Epithelium – It is made up of thin flat cells like floor tiles. Each cell has a dense mass, the nucleus at the center separated from the rest of the cell by a nuclear membrane. The less dense portion outside the nucleus is the cytoplasm surrounded by a cell membrane.

Cuboidal Epithelium – It is made up of tubules that are lined with cube-like cells joined together by a basement membrane.

Columnar Epithelium – This consists of cells taller than wide with their long sides adjacent and supported below by a basement membrane.

Ciliated Epithelium – A ciliated cell bears on its exposed surface numerous short hair like extensions known as cilia. These cilia beat in one direction, the adjacent ones acting in unison so that small particles or materials on the surface are moved along.

Grandular Epithelium – This is specialized for secreting products necessary for use by an animal.

Epithelial cells specialized to receive certain kinds of external stimuli are sensory cells.

The inner lining of the reproductive organs (testis and ovary) is made up of an epithelium specialized for the reproduction of reproductive cells or gametes, the sperm and egg cells.

Cytology

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What is Cytology

Cytology

Cytology

The unit structure of all living things is the cell. The size and form of the cells vary, but each kind is fairly uniform in a given species of animals. The study of the cells is called cytology. For much cytological study with a microscope, cells or cell groups are killed and fixed by chemical reagents or frozen, cut into thin sections, mounted on glass slides and stained to differentiate the parts.

Cell Division

Most organisms grow and develop by multiplication, enlargement and differentiation of their cells. The process is called cell division. In multicellular organisms, adult form is attained by increase in number and size of cells and cell differentiation from zygote to maturity. In unicellular organisms, cell division serves also as a form of reproduction. Sexually reproducing forms also depend on cell division for the formation of sex cells or gametes.

Cell division consists of two distinct but integrated activities, nuclear division or karyokinesis and cytoplasmic division or cytokinesis. The two types of nuclear division: mitosis and meiosis are characteristic of most plant and animal cells. Mitosis occurs in somatic and reproductive cells while meiosis occurs only in reproductive cells. Mitosis ensures the equal distribution of each kind of chromosome to each daughter cell, while meiosis results in the reduction of the chromosome number in each daughter cell.

Mitosis is similar in both plants and animals. It is smooth continuous process but may be divided into stages or phases for convenience. These stages are prophase, metaphase, anaphase and telophase. Between two mitotic cycles, the cell is said to be in interphase.

Interphase

The interphase cycle may be defined as the entire sequence of events transpiring from the close of one nuclear division to the beginning of the next one. The cell in the stage does not show any sign of actual division. The cell is divided into two parts: the nucleus, a central deeply stained region and the cytoplasm, peripheral less stained region. The nucleus is surrounded by a definite wall the nuclear membrane which encloses one or two deeply staining bodies, the nucleoli. Minute bodies called chromatin granules are scattered around the nucleus. The cytoplasm which in life is filled with watery fluid is surrounded by the cell wall.

Prophase

As the cell enters the prophase stage, the chromosomes progressively shorten and thicken to form individually recognizable, elongate, longitudinally double structures arranged randomly in the nucleus. The two sister chromatids of each chromosome are closely aligned and somewhat coiled on themselves. They are held together by strands in the specialized region, the centromere. The nucleolus as well as the nuclear membrane gradually disappears. As prophase progresses, a mitotic apparatus, the spindle (and associated structures) begins to form; it occupies a large portion of the cell volume at the end of prophase. The mitotic apparatus consists of slender microtubules arranged along the long axis of the spindle. Some of the microtubules are continuous from pole to pole of the mitotic apparatus; these are the continuous fibers. Groups of others, the chromosomal fibers, extend from one pole or the other to each chromosome. A third type of microtubule, the interzonal fibers run between the centromeres of the separating daughter chromosomes later on in anaphase. In animal cells the spindle may be seen to arise at both ends; each is composed of black dot, the centriole with astral rays or asters radiating from the ends of the spindle.

Metaphase

At this stage of the chromosomes are shortest and thickest. The centromeres of the chromosomes occupy the plane of the equator of the mitotic apparatus although the chromosomal arms may extend in any direction. The sister chromatids are still held together by connecting chromatin fibers at the centromere regions.

Anaphase

This is characterized by the separation of the metaphase sister chromatids and their passage as daughter chromosomes to the spindle poles. It begins at the moment when the centromeres of each of the daughter chromatids become functionally double and ends with the arrival of the daughter chromosomes at the poles.

Telophase

The arrival of the daughter chromosomes at the spindle poles marks the beginning of telophase. The events of prophase occur in reverse sequence during this phase. New nuclear membranes are constructed, the mitotic apparatus gradually disappears, the nucleoli are reformed and the chromosomes resume their long, slender, extended form as their coils relax. Cytokinesis takes place during structure that appears as a dark line at the middle of the cell. Early steps in cytokinesis include the formation of vesicles in the midplane of the mitotic apparatus, the coalescence of these vesicles starting at the center of the spindle to form a phragmoplast. The cell plate forms within the phragmoplast gradually extending centrifugally and dividing the phragmoplast into two parts before the latter disappears. In animal cells cytokinesis is accomplished by the formation of a cleavage furrow. The telophase stage ends upon the reorganization of two new nuclei and their entry into the interphase stage.

The Microscope

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The Parts of the Microscope

Compound Microscope

The Compound Microscope consists of the following parts:

Base - This is the part of the microscope which is U-shaped structure located at the bottom and which is used to support the microscope.

Pillar – This is a short part arising from the base and which is screwed to the succeeding part.

Arm – This is where you put your hand to hold the microscope.

Drawtube – This tube holds the eyepiece of the microscope.

Eyepiece or Ocular Piece – This is a magnifying part of the microscope that is found in the drawtube.

Revolving Nosepiece – This part is found at the lower end of the drawtube where the objectives are screwed.

Objectives – There are two or more objectives attached to the revolving attached to the revolving nosepiece. The magnifying capacity is found at the side of the objective: Scanner, x4, Low Power Objective, x10; High Power Objective, x40 or x60, and Oil Immersion Objective, x100.

Adjustment Screws – This is used to raise and lower the tube. There are two of these: the large one is the coarse adjustment screw and the small one is the fine adjustment screw.

Substage – This is found beneath and stage and consists of the condenser which centralizes the light and the Iris Diaphragm which regulates the amount of light entering the microscope.

Mirror – This reflects light through an opening in the stage to illuminate the object, It has 2 faces: flat and concave.

Care of the Microscope

Handle the microscope with great care. Carry it vertically with one hand on the arm and the other hand supporting the base. Some parts are easily detached and are likely to break when they fall.
Any broken or missing part of the microscope should be reported to the instructor immediately.
Clean the lenses with lens paper or fine cloth. Do not use your fingers or any coarse material as this may scratch the lenses.
When using fresh mounts, do not tilt the microscope. Do not allow water to get on stage. Dry the underside and edges of your slide before putting it on the stage.
When it is necessary to move the slide while looking through the microscope, do not use the clips.
Do not detach or remove any part of the microscope.

How to use of the Microscope

Align the low power objective with the ocular.
Open the Iris Diaphragm.
Adjust the mirror to the source of light. Look through the eyepiece. The entire field of the microscope should be lighted uniformly.
Place a slide with a mounted specimen at the center of the stage.
By using the coarse adjustment screw, lower the tube of the microscope until the objective is about one or two mm from the cover glass.
Look through the microscope and raise the tube until the image of the specimen comes into view.
If you cannot see the specimen, it may not have been placed at the center of the microscopic field. Center the specimen and repeat the whole process until you see it.
While looking through the microscopic move the objective up and down with the use of the fine adjustment screw until a clear image is seen.
For a detailed study of the parts of the object, put the high power objective in place. Use only the fine adjustment screw when focusing under high power objective.

Ecology

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Ecology

What is Ecology?

Ecology is the science that studies the relationship between the organisms and their environment. The environment means the immediate surroundings upon which plants, animals and microbes depend for carrying on their functions. Plants need air and water and sunlight to carry on photosynthesis; all animals ultimately depend on plants as source of organic food and vitamins; microbes play an important role in the decomposition of the remains of plants and animals. Thus we see how living things depends upon one another and their physical environment for their survival.

What Autecology and Synecology means?

Ecology may be studied from different viewpoints or approaches. Traditionally, it is divided into autecology and synecology. Autecology studies the individual organism or an individual species – the organism’s behavior by means of which it adapts to the environment, as well as its life history or life cycle. Synecology studies the organism “as groups associated as a unit” (Odum). Thus, the zoologist who studies the life (feeding, reproduction, etc.) of the common frog, Rana limnocharis, in the pond and meadow is doing autecology. On the other hand, the zoologist who studies the pond or meadow in which the frog lives together with the plants and other animals (insects, worms, snails, etc.) that thrive therein is doing synecology.

Levels of Organization

Modern ecology emphasizes that concept of levels of organization, i.e., the population and the community. Population in the ecological sense refers to “groups of individuals of any one kind of organism”, hence species. Community, ecologically speaking includes “all the populations occupying a given area”. “The community and the non-loving environment; functions together as an ecological system or ecosystem”.

Considered as “the largest and most nearly self-sufficient biological system we know about”; is the biosphere or ecosphere. It includes all of the earth’s living organisms interacting with the physical environment as a whole so as to maintain a steady-state system intermediate in the flow or energy between the high energy output of the sun and the thermal sink of space. For purposes of specialization, ecological relationships in the biosphere may be studies in distinct habitat zones.

What Habitat and Niche means?

Living organisms occupy a definite space, its home or habitat each and every species performs a definite function or ecological role in its habitat, its niche. Thus, the pond and the meadow constitute the normal habitat of the common frog. Rana Limnocharis. In the pond, where it feeds on plant food during its larval existence, its ecological role there is a herbivore; in the meadow, where it feeds on insects, worms, snails, etc., function (as an adult) is carnivore.

What are Habitat Zones?

In the so-called “habitat approach”, the ecologist studies the organisms according to habitats. The aquatic habitats include the marine, estuarine and fresh-water environments. The environmental conditions that determine the distribution of life in these habitats include the substratum, salinity, temperature, hydrostatic pressure etc. The striking contrast in species diversity and adaptations between the coral reef communities and the hadal communities is a reflection of the differing ecological conditions in these two extremes of the marine environment.

The terrestrial habitats include the mountain, peneplains, wetlands and deserts. The distribution of life on land is controlled by such factors as soil quality temperature, humidity, atmosphere pressure (wind), precipitation, etc. Vegetation which is important to animals as shelter and source of plants foods, limits the ecological distribution of terrestrial animals.

What do Biogeochemical Cycles and the Balance in Nature means?

Nature is structured in such a way that the chemical elements in the atmosphere, hydrosphere (oceans) and the earth crust tend to circulate in the biosphere in characteristics cycles back to the environment. In the cycles of elements (carbon cycle, oxygen cycle, nitrogen, mineral and water cycles) we see the frugality of nature in using and reusing all the existing elements—never destroying matter only changing its form. The symbolic, parasitic and saprophytic relationships take on a new significance in the scheme of maintaining a balance of nature.

Unless disturbed by natural catastrophes, the balance in nature remains undisturbed. Human activities tend to upset this balance, yet it is within man’s power to restore it.

Man today is suffering from environmental crisis. The volcanic eruptions, earthquakes, perennial floods and drought, scorching heat, etc., that afflict many places or earth today are but signs of how man has abused his environment. His survival alone is not at stake, even the myriads of plants and animals species around him are threatened of extinction.

How is Wildlife Conservation?

The wild life that thrives in the forests and the seas are vital for human existence. Let alone their aesthetic values, man profits from them for food, medicine, articles of clothing and shelter, etc.; if properly harnessed man can enjoy their commercial values for ever. However, because of avarice and greed, these creatures are doomed. If man desists not from the wanton exploitation, destruction of the wildlife and their habitats, this planet will be reduced to a global desert.

Many countries are well aware of the importance of conserving wildlife. Thus game laws are established for their protection (by limiting the hunting season and the hunter’s bag) and certain tracts of forests, wetlands and wildlife denizens. Even treaties are forged among nations to protect the migratory species in the course of their international wanderings.

For the success of these ecological plans and operations, what is most important is public cooperation. However, the general public needs to be educated first. If there is one ecological message which this course should impart to you; it is your moral responsibility to help in the wildlife conservation crusade.