Biological Science

MODERN CELL DOCTRINE

2011-10-13T06:38:00.000-07:00

The postulation of the cell theory by schleiden and schwann generated more interest in biologist to investigate all aspects of cell and consequently , the knowledge about cells became rich ;more facts emerged will respect to cells .I n light of the available facts,Rudolph Virchow [1858] made another biological generalization that new cells can arise only from pre-existing cells,i.e., ominis cellula e cellula , leading to the establishment of the law of lineage .This made it clear that the succession of cells is continuity of life and the vital function of the body such as metabolism , growth , inheritance , diesease , aging , death , etc ., are varied aspects of the funxctioning and the behavour of the cells .These facts modified the cell theory into modern cell doctrine .The main postulates of the doctrine include : 1.The cell is the structural and functional unit of all living things. 2.It is the unit of development of all living things . 3. All cells come from pre-existing cells. 4. They are hereditary units 5. The cell is the unit of pathology. Two types of Cells The cells of organisms belong to two basic categories : the prokaryotic cells and the eukaryotic cells .The prokaryotic cells lack the membrane bound nucleus.Nor they have mitochondria ,golgi body and lysosomes .Their so called nucleus has just a single chromosome , consisting of a DNA molecule , without histone and lying exposed in the cytoplasm Their enzymes involved in the protein synthesis and respiration , are associated with the cell membrane .Cell of bacteria and cyano bacteria [blue green algae ] are prokaryotic cells . The eukaryotic cells are true cells of animals from from protozoa to mammalia , and plants from algae to angiousperms .These cells have a distinct nucleus ,bounded by a nuclear membrane .The nucleus has nucleolus and varying number of chromosomes.

PHYSICAL NATURE OR STRUCTURE

2011-09-27T02:59:00.000-07:00

It is often coluorless or greyish ,translucent and somewhat viscous semiliquid , that is , gelatinous in texture .Its viscosity varies from cell to cell in the same organism ,and from organism to organism .It is heavier than water .Some substances of the protoplasm such as sugars ,salts and simple acids and bases ,etc ., form crystalline or true solution but others exist in colloidal solution .Thus ,the protoplasm may be called a complex crystallo-colloid mixture .In colloidal system ,samll finely divided particales of matters [0.001u-0.1u] are suspended in a continuos medium .The colloids frequently posses glue-like consistency and are not crystalline in structure .A very viscous colloid is called a gel and more fluid colloid a sol . Sometimes sol and gel are converted into one another .Thus protoplasm is a reversible colloid , that is , it changes into sol or gwel when necessary .However it exists normally in a state between a sol and gel . View about physical structure .Under light microscope the protoplasm of the different cell shows different appearance or different structure , even the same cell shows different structures at different times .This has led the workers to think differently about the structure or appearance of the protoplasm. The view of the workers are in the form of the following theories : 1. Fibrillar theory .This theory , proposed by flemming , states that the suspended colloidal particles are in the form of fine fibres . 2. Alveolar theory .This theory ,proposed by Butschli [1892] ,holds that the protoplasm is an alveolar strucute .It appears to be a foaming mass of globules embedded in a viscid medium . 3. Granular theory .According to this theory , the protoplasm presents , a granular appearance ; many fine granules are evenly distributed in a liquid medium .This theory was proposed by altman [1893] . 4 Reticular theory . This theory states that the structure of the protoplasm is reticular , the suspended particles are in the form of a network of fibres.

LIFE SUBSTANCE: THE PROTOPLASM

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What is life ? What is to be alive? These are the questions which have not been satisfactorily answered even to this date .Many attempts have already been made and are being made to disclose the mystery of life but we have still not succeeded .We know only this that the life is the quality of the living substance,that is , the protoplasm , and it is always associated with the protoplasm . Thus protoplasm is the physical basis of the life. Discovery of Protoplasm The protoplasm in the cell was observed by corti as early as 1772 .In 1835 ,Dujardin noted the constant occurence of a jelly -like substance ,unlike ordinary gelatin or albumin in cells of certain simple animals ,for which he proposed the name sarcode .He recognised it as the living material of these animals .Four years later ,Purkinje [1839] coined the name protoplasm for the sarcode .In 1846 Von Mohl also proposed the name protoplasm for a substance which he found in the cell of plants in 1861 Max Schultze observed the cell contents of protzoa and of plants and animal cells .He concluded that the contents of all cells were essentially similar, and he proposed a theory which was later named protoplasm theory by Hertwig [1892] .This theory postulates that the cells are accumulation of the protoplasm with the nucleus and a cell membrane .This theory established the close similarity of the living substance of animals and plants .Huxley [1968] defined protoplasm as the physical basis of life. STRUCTURE OF PROTOPLASM The protoplasm is a complex mixture of many chemical substances .It keeps living thing alive .Rather , it houses the life .Therefore , it is known as life substance .The body of all living organisms is composed of the protoplasm .The body and cells of different organisms differ greatly from one another but there is a basic similarity in physical and chemical structures of their protoplasm .The living state of the protoplasm is due to its composition and physico-chemical properties.

SIGNIFICANCE OF VIRUSES IN ORIGIN OF LIFE

2011-09-24T02:30:00.000-07:00

Since viruses have characteristics of both living and non-living objects with very simple organization as very minute particles of nucleo- protein , it may be concluded that the primitive life was like viruses .Their posession of the characteristics of both the living and non-living objects suggests that non-living inorganic substances evolved into organic substances before the origin of the primitive life.Further , since viruses may synthesize DNA and protein in the host cell , they may be taken as the first forms of life as per Oparin's explanation of the origin of life .However , the modern view about the viruses is that they have originated from the early existing cellular form of life and therefore , they can not be taken as the early primitive forms of life .Moreover,C.F.Luria [1971] ,the noble prize winner , has called them bits of heredity , looking for a chromosome. ECONOMIC IMPORTANCE OF VIRUSES Viruses are responsible for several diseases of plants and animals. In plants , they cause leaf roll of potato , rugose mosaic of potato, leaf curl of tomato , leaf curl of papaya ,mosaic of papaya ,yellow ringspot of lady finger ,mosaic of tobacco ,etc. In man ,the viruses cause small pox ,influenza,common cold ,mumps ,measles ,rabies,poliomyeletis [polio],etc. The HIV [Human immuno deficiency virus] cause AIDS [acquired immune deficiency syndrome ] which drastically cut the life of men and women .Besides , the viruses are supposed to cause cancer and tumor formation.

HOST'S DEFENCE AGAINST VIRAL INFECTION

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In order to combat the viral infection, the host -cells synthesize special coded proteins called interferons .These by intact animal or cultured cells in response to the viral infection ,and believed to be body's first line of defense against viruses .In fact,these inhibit replication of viruses.Various interferons, known so far ,fall under three main categories [1]IFNa,[2]IFNb,[3]IFNy .All vertebrates species are able to synthesize interferons . However ,normal cells do not generally synthesize interferons until these are induced to do so .Their synthesis is induced by the viral infection .The different kinds of the host-cells .The IFN -a , is produced predominantly by leucocytes ,IFN-B mostly by fibroblasts and IFN-y only by lymphocytes . Antiviral Activity of Interferons Interferons were first recognized to interfere with the viral infwection in cultured cells .In intact animals these are produced soon after the virus infection , leading to decrease in the virus -production .Apparently ,these act as antibodies against viruses .In fact, these induce synthesis of other proteins which inhibit the viral replication . NATURE OF VIRUSES Since the discovery of viruses , the controversy has been going on whether they are living or non- living objects because they have some of the characteristics of the both .Many biologists consider them non-living because of their following characteristics : 1. Viruses are not in the form of cells.They lack cell membrane and cytoplasm . 2. They are composed of aggregations of the units of heredity enclosed in a protein sheath or coat . 3. They do not ingest food . 4 .They do not have energy producing structure nor they respire like cellular life . 5. They can be crystallised like an ordinary substance and stored for long periods in bottle .

SHAPE AND SIZE OF VIRUSES

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Viruses are such smaller than the smallest bacterium .Their size ranges from 30to 300 nm .That is why their structure was not known before discovery of the electron microscope . Viruses have assumed different shapes .Some are helical or rod-shaped,e.g., tobacco mosaic virus [TMV] and influenza virus .Many viruses are spherical but on close examination ,their shape is found to be many sided or polyhedron.e.g., adeno virus ,herpes virus ,turnip yellow mosaic virus [TYMV] etc .Some viruses have complex shape .For example ,T4 bacteriophage ,T4 bacteriophage ,or virus, vaccinia virus,etc.
Structure of Viruses The electron microscope has shown that all viruses exist as discrete particles ,each of which is called a virion .In other words ,a virion is an individual of a virus .All viruses have a similar organization;avirion has acentral core of coiled strand of a nucleic acid,DNA or RNA and a protein coat called capsid which surrounds the core .Some viruses ,for example , herpes virus,have an outer envelope ,composed of polusacchearide or lipoprotein. The capsid consist of a number of protein subunits called capsomeres .The arrangement of capsomers arround the core imparts a particular shape to virion of a virus.The animal viruses , bacteriophages and cyanophages have DNA whereas plant viruses other than bacteriophages have RNA .

HOST AND TUPES OF VIRUSES

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The available records shows that the viruses attack bacteria ,cyanobacteria[Blue-green
algae],flowering plants and animals,Depending on the kind of the living organism attacked by them ,the viruses belong to the following four types; 1.Bacterial viruses.usually called bacteriophages,these viruses attack bacteria .If a small amount of bacteriophage suspension is added to a liquid medium with rich bacterial growth , then the turbid liquid medium becomes clean and full of bacteriaophages. 2.Blue-green algae viruses.These viruses usually called cyanophages,attack blue-green algae ,now called cyanobacteria. 3.Plant viruses .These viruses attacks flowering plants ,e.g.,tobacco-mosaic virus,tomato-wilt virus ,yellow and vein mosaic virus,etc. 4.Animal viruses .These viruses attack animals and include influenza virus, rabies virus,pox virus,mumps virus ,polio virus ,measle virus ,vacinnia virus ,adeno virus ,etc. DNA and RNA Viruses .Depending on the presence of DNA or RNA,the viruses are either DNA virus or RNA virus .The DNA virus contains DNA in its core ,whereas the RNA virus has RNA in its core .The bacteriophages are DNA virus and plant viruses are either DNA or RNA virus . Reverse transaction viruses .These are animal viruses ,strongly linked to cancer or tumor formation ,and have RNA in thier core .Usually the DNA makes copy of sequence of its nitrogenous bases in the RNA [transcription], but in these viruses ,the RNA makes copy of sequence of its nitrogenous bases on the DNA [reverse transcription] hence these are called reverse transcription viruses or retroviruses in the abbreviated form .The hepatitis B virus , Epstein-barr virus ,herpes virus and papilloma virus are examples of retroviruses.

LIFE STYLE OF VIRUSES

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The viruses become active and reproduce within the cells of other organisms but they remain inert outsides the cells ,showing no activity .Evidently ,they are obligate parasites .While infecting or attacking other organisms they show host specificity .In general ,viruses are specific in attacking hosts, a particular virus attacks a particular host ,choosing one and the same organ or closely related organs .However ,a few viruses ,for example ,rabbies virus and vaccinia virus can infect man as well as cows ,sheep,rabbits,monkeys ,rat ,mice ,guinea pigs,hamsters ,chick embryos ,etc. In certain instances ,there is much precision in host specificity ;there are some viruses which attack only a particular kind of tissue .For example ,viruses of pox and measles attack and tomato-wilt virus attacks only leaves of tomato .Certain viruses ,attack bacteria infect only male cell but not the female cell. Many viruses remain concealed within the host cell for a very short to a long period without showing any adverse effect on the host .Sch viruses are known as latent virus .Some viruses that infect two hosts ;remain latent in one host but become virulent in another .For example a virus known to exist and reproduce in potato without showing any pathogenic symtoms .become effective on transfer to tomatoes . Nomenclature of Viruses It appears that the virus nomenclature is more arbitrary and in confused state.Instead of adopting the binomial nomenclature ,viruses are named after the disease they cause ,for example ,pox virus,polio virus , tobacco -mosaic virus ,tomato wilt virus ,cherry-ringspot virus ,etc ., or after the tissue or organ they attack ,for example ,the ,the adeno-virus that attacks adenoids .In certain cases ,the naming is more arbitrary ,for example ,the polyoma virus is named so because it is able to cause numerous kind of tumors .The code number are often used to name the bacterial viruses .For example ,viruses that attack the intestinal bacteria,Escherichia coli have been named by using T with numeral as suffix from 1to 7 [T,toT1] .

VIRUSES

2011-09-17T05:00:00.000-07:00

Viruses are the smallest objects that can pass through the filter capable of trapping even the smallest bacteria .These are very minute particles of nucleoproteins which can be usually viewed only under the electron microscope ;however, some are so minute that they can not be viewed even under the electron microscope .Inspite of this ,scientists , better say ,virologists [specialists of viruses] ,have evolved special techniques to study their structure ,behaviour and reproduction .These deserve special consideration in our survey of the distinction between the living and non living objects because they show of the characteristics of both and thus ,they form a connecting link between the two types of objects .In order to evacuate them more clearly as alink between the two types of objects ,information about their structure and lifestyle is essential .Such information is also important due to this fact that the viruses are pathogenic ,causing harmful diseases in man ,animal and plants . Discovery of virus .People were not familiar with viruses till the end of the 18th century but they definitely knew them to cause diseases .First of all ,Edward Jenner [1796] tried to know about small pox and then Louis Pasteur [1882] tried to know about the virus , causing rabies .However ,in 1892 Ivanovsky discovered that the bacteria -free extract of the tobacco plant ,already affected by the tobacco-mosaic disease,was successful in causing these diseases in healthy tobacco plants .this fact was confirmed by Beijernick [1898] and he named this extract or filtrate as contagium vivum fluidum which ,later , was named filterable virus ,and finally ,virus literally meaning poison .The first animal virus responsible for the foot-mouth disease of cattle was discovered by Reeds in 1902 .The bacteria attacking viruses were discovered for the first time by twort [1916] in england and then by d'Herelle [1917] in France .Later on ,W.M.Stanley [1935] was able to isolate Tobacco Mosaic Virus [TMV] from the diseased tobacco leaves .Since then many more viruses have been discovered and the diseases caused by the m have been recognized CHARACTERISTICS OF VIRUSES Viruses are curious and interesting .These exhibit the following characteristics : 1.Virus is a very minute particle of nucleoproteins which can be seen only with the help of the electron microscope . 2. These are very simple in organization and lack cellular structure . 3. These are very simple in organization and lack cellular structure . 4. These are composed of DNA or RNA ,single or double stranded and proteins as a sheath ,called capsid . 5. These donot have cytoplasm and plasmalemma [plasma membrane ].

EVIDENCES IN SUPPORT OF BIOCHEMICALORIGIN OF LIFE

2011-09-11T02:42:00.000-07:00

Evolution of complex organic molecules from simple molecules ,as held by Oparin,has been proved by many scientists all over the world .This is well supported by experimental or laboratory studies.in this context ,Stanley miller [1953] has taken alead to provide experimental proof . Stanley Miller's Experiment IN 1953 ,Stanley Miller performed a simulation experiment under guidance of his professor ,Harold Urey to test hypothesis of biochwmical origin of life .In this experiment ,he tried to create thse conditions that might have existed in the primitive atmosphere .For this he built an apparatus as shown in Fig .2.1 to circulate CH4,NH3,H2and H20 and pass to circulate CH4,NH3,H2andH2O and pass electric discharges.The assemblyu of the apparatus consisted of two flasks- one large and another small , a condenser and glass tubes .Two tungsten electrode ,connected to an electric source were fitted in the large flask to provide energy of electric discharge ,simulating effect of lightning of the primitive atmosphere and for this reason ,Stanley Miller's apparautus is called Spark . Discharge Apparatus .The large flask contained a mixture of CH4,NH3 and H2[2:1:2] and the small flask had water .The experiment started with switching on the electric source and boiling the water and it continued for a week .Then , on observation ,Miller found a dark coloured condensed liquid .He collect it and analysed chromatographically .The analysis showed that the fluid was a mixture of sugars,amino acids [e.g., glycine ,alanine ,aspartic acid,etc.]and fatty acids .Miller's this finding supports Oparin's theory of origin of life that during course of origin of life , simple molecules evolved into complex organic molecules . Other Evidences Oparin's view has also been supported experimentally by Melvin and Calvin[1951] , Sydney.F.Fox[1964] and Abelson ,Oro and Kamat[1960,1965 ] .The latest support comes from Dr.H.R.Khorana [1968] who has synthesized a DNA molecule ,consisting of 77nuccleotides ,in a test tube .For this synthesis ,Dr.Khorana's synthesis of DNA molecule suggest that during the course of origin of life ,nucleic acids would have formed by linking together of nucleotides in the primitive ocean.

HABITATS

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Animals are found almost everywhere on the earth .They are found in fathomless depth of the ocean ,at the highest peak of the mountains ,freezing cold of the polar region or in scorthing heat of the deserts.Each of these regions may have its own peculiar fauna [stock of animals] The animal may inhabit the salt water of the sea or the fresh water of the rivers and ponds They may live on or in the soil ; some may take to air and some to the trees .Many animasl reside on or in the body of other animals as parasites . Marine habitats . About three- fourth of the eath surface is covered by the water of the oceans .The salt water of seas and oceans serve as home of the marine animals .These may live either on the sea-beach or in the deep depth of the sea or on its bottom .They may be found in the open sea .Those marine animals which live on the sea beach either in the sand or remain attached to submerged rocks are called littoral animals .Those who lived at great depth are called deep sea or abyssal animals , whereas those living on the bottom are called benthonic animals .The animals found on the surface of water are pelagic animals; they swim freely [nektons] or float [planktons] . Fresh water habitats. Animals which occupy fresh water bodies such as rivers, lakes ,ponds, and swamps are called fresh water animals .Such animals may mostly occupy either running or stagnant water The animals living in the stagnant water [ponds, lakes,etc.] are called lentic forms ,whereas those living in the running water [streams ,rivers] etc.] are called lotic forms .The surround8ings is hypoyonic to their body .Therefore , they have water- regulatory mechanism in their body . Terrestrial habitats. Animals living on the land are called terrestrial animals . They may live on the surface or beneath the surface.Those animals which live beneath the surface if the soil are called subterranean or sub terrestrial animals .The surface dwellers may be found on plains , on rocks , no deserts or in the damp forests .Their locomotory structure fit well for the movement of the land . Besides ,some animals have selected air or trees as their habitats .Those animals which inhabit air are called aerial animals.They spend most of their time in the air and come to land for the rest .Birds and insects are example of aerial animals.The animals living onthe trees are called arboreal animals .They spend most of their time on the trees but do come to land for feeding or other activity for avery short period of the day and night .The squirrel is an arboreal animal .

ANIMALS

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The animals are living objects with heterotrophy , rapid responsiveness ,very high level of adaptability and a compact body that grows only upto a certain age and lacks chlorophyll and cellulose .They have definite shapes and different level of body organization , in habit different parts of the environment and form association with other living organisms. Shapes of body ;Most animals have definite shape of their body and each animal is usually recognised by the shape of its body .The shape of the body is expressed in term of symmetry, depending on which the body shape is of the following two types ; [1] Symmetrical .When parts of the body are arranged in such a pattern that it can cut into two equal halves through one or more planes the body is said to be symmetrical [regular in shape] . [2] Asymmetrical .If the body parts are arranged in such a way that the body can not be cut into two equal halves through any plane , the body is said to be asymmetrical[irregular in shape] .Amoeba and few other animals have asymmetrical body . The symmetry of the body may be spherical ,bilateral or radial. A ball- shaped body has spherical symmetry .It can be cut into two equal halves along the longitudinal axis ,it is said to be bilaterally symmetrical .The body of man bilaterally symmetrical .The earthworm and frog also show similar symmetry .Some animals have abody in which body part radiate out from the centre ,it is said to be radially symmetrical .The bodty of star fish is radially symmetrical and so is the body of Aurelia and hydra [both coelenterates]. The symmetry of the body is associated with the polarity and surfaces of the body .The distinction of anterior and posterior ends in the body is called polarity of the body .The end of the body that remain toward the direction of the movement is called anterior end and the end opposite to this end is said to be the posterior end of the body .The anterior end is characterised by the presence of mouth and the posterior end by the presence of cloacal aperture or anus .Besides , the anterior and posterior end ,two more ends ,the proximal and distal ends are also referred in context of the description of the body or an organ .The proximal end is the end near the point under reference ,whereas the distal end is away from the point under reference .The terms proximal and distal are also used as prefix to parts . Three surfaces are distinguishable in the body which remains towards sky or away from the body of most animals ;these include dorsal , ventral and lateral .The surface of the body which remains towards sky or away from the substratum during the movement is called dorsal surface lies between the dorsal ventral surfaces on the sides .It is represented by right and left sides of the body.In man the head end is anterior end and anal end the posterior end .The back of the human body is dorsal surface , whereas the dorsal chest is the ventral surface .

ZOOLOGY

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Zoology is a vast science which deals with animals hence ,it is usually quoted with as animal science . It deals with all those aspects which are related to maintainence and continuity of the animal life .These aspects include the body organisation ,functions of body parts , in heritage of characters ,evolution ,responses and behavior , relationship with environment, etc. Branches of Zoology For sake of convenience ,Zoology , a vast science , has been divided into different branches which include ; [1] Morphology .It deals with gross structure and shape of different animals .It has been divided into Anatomy, dealing with the study of internal structures with unaided eyes , and Histology , the study of the internal organs and tissues with the help of microscope . [2] Cytology .It deals with the cytoplasm and structural detail of cells. [3] Taxonomy .It is the study of principles and laws relating to classification of animals and their nomenclature. [4] Evolution . It deals with the study of origin of life , formation of different forms from the primordial life and relation ship between existing [extent] and extinct animals. [5] Paleontology . It deals with the remains of animals of bygone ages,i.e., fossils . [6] Zoogeography.It deals with the study of the distribution of animals in space and rocks of the earth . [7] Genetics .It deals with the study of the distribution of animals in space and rocks of the earth from generation to generation . [8] Zooecology . It deals with the study of animals association with other organism and abiotic environment , or deals with the relationship between animals and their surroundings . [9] Eugenics . It deals with the method of improvement of the human race , involving already established principles of genetics . [10] Ethology . It deals with the study of improvement of the human race, improving immediate environment that surrounds man .[12] Embroylogy .It deals with the study of improvement of human race by improving immediate environment that surrounds man . [13] Endocrinology .It deals with embroys and their development .The developmental biology is synonimous with the embroylogy . [14] Physiology .It deals with the study of function of the body parts. [15] Osteology.It is the study of the bones of different animals . [16] Enzymology.It deals with the study of the nature , strucutures and the function of enzymes in the body of animals .

DIFFERENCE BETWEEN TWO CATEGORIES LIVING OBJECTS [ANIMALS vsPLANTS]

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Most living object can be assigned to one of the two great categories of plants and animals but some microscopically small living objects have characteristics of both .Plants and animals have common ,to a greater or lesser extent almost all character of the living objects but there are some fundamental differences between them .These include the following ; [1] Method of feeding ; Animals take food in that is chemically complex [i.e., composed of macro molecules ]. It consists either of plant products or of animals that feed on plants .Thus , they are hetrotrophs . The complex food is reduced to simpler material by the process of digestion , and in this form it is taken up by the body .On the contrary , plants take in very simple substances as food which consists of simple molecules ,namelyCO2, from the air ,and water and mineral from the soil .In their leaves ,they combine CO2,and water to form a simple sugar , the glucose using energy of the sun to affect the change ,a process called photosynthesis .From the glucose so formed and mineral salts absorbed from the soil ,green plants make any of the substances needed for their existence .Obviosly plants are autotrophs and they do not depend on any source for their food . [2] Chlorophyll .The green color of the plants is due to the presence of compound called chlorophyll ,which is not present in animals .The chlorophyll is important in absorption of the solar energy , and its presence in animals .The chlorophyll is important in absorption of the solar energy, and its presence indicates fundamental difference between nourishing process of plant and animals .However ,fungi and most bacteria lack chlorophyll and therefore , must obtain both their nourishment and their energy from the food they consume , much as animals do .[3] Cellulose.A considerable proportion of the plant body is composed of a complex polysaccharide called cellulse .It is not present in animals . [4] Movement .Most of the animalos can move their whole body ,and are able to change place .On the contrary ,most plants cannot move their whole body , for example ,opening and closing of petals of certain flowers ,and movement of parts due to the growth .However ,microscopic plants move as freely as microscopic animals .[5] Growth .The animals grow only upto a certain age after which they donot grow till death.Their body body parts proportionately in all directions .On the contrary ,plants grow through out life and their growth is terminal ,i.e., they grow more along their length than width . [6] Organisation of body .In animals , parts are mostly placed in the body , whereas in plants , the parts are mostly placed on the surface of the body . [7] Receptors . The receptors are unique to animals ; they recieve stimuli and keep animals informed about the environmental changes , but in contrast with the animals ,the plants lack receptors . [8] Excretion . Animals remove out toxic wastes of their body but this doesnot takes place plants .

LIFE AND ITS CHARACTERISTICS

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Life ; Living organisms have life and that is why they are distinct from non-living objects .But a very pertinent question arises as what is life ? The other question may be asked such as what is shape of life and how has it come into existence ? Honestly, no categorical answer is available to these questions .However , some speculations or hypothesis are available in this context .Some believe that life is a power state of the body , others have taken life as steady and dynamic state of the living matter ,i.e., the protoplasm and certain others have considered it to be the total sum of chemical reactions taking place in the body of the living organism.But many others have explained the life as the body's ability to utilize and convert energy .These definations suggest that the life is an abstract phenomenon. Characteristics of Living Objects It is certainly difficult to define life but every object possessing life shows certain activities which are attributes of life .These are common to all living objects or living organisms and therefore are refered as to characteristics of life or life forms .On the basis of these characteristics , the living objects can be easilly distinguished from the non-living ones . These include the following; [1] living objects have definite shape and size and therefore , every object has a distinct appearence and that is why one living objects or organism can be ditinguished easiy from another . [2] Living object are highly ordered and possess protoplasm.Body of all living objects is composed of living matter called protoplasm ,whose chemical composition includes large complex such as proteins ,carbohydrates, fat, water and nucleic acid .Such combination of chemical is not found in non-living objects. [3] Living objects show cellularity .In every living object the living matter is divided into unit structures called cell .Body of some living objects is made of only one cell ,whereas the body of other living objects is made of only one cell , whereas the body of other living object is formed by more than one cell .On the contrary , the body of non-living objects doesnot show cellular organization . [4] Livng objects move .Living objects are able to move their body part of whole body .Most animals are able to move their whole body and move from one place to another .The movement involving change of place ,is called locomtion. [5] Living objects feed and utilize food after procesing .Every living object takes in food or better say chemicals. Animals take food from plants or other animals which is feed on plants .The food of animals consists of complex organic molecules .In their body , the complex molecules are changed into simpler molecules [digestion] which are absorbed and again organised to form complex molecules which become part of the protoplasm[assimilation] and also supply materials for growth ,repair and energy release . [6] Living objects grow . Every living objects shows increase in size and weight . This phenomenon is called growth .The growth in organism is caused by a process which involves the intake of new materials from the outside and their subsequent mixing with the protoplasm as its part.

LIVING MATTER

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All matters of the universe are formed by the same structural units hence they are basically similar.Inspite of this the different objects are categorised everywhere as living objects and non-living objects.The matter that forms every living object is a greyish , semitransparent and viscous mixture ,named protoplasm by purkinje [1839] and later by hugo von mohl [1846] .This is refered to as a marvellous super mixture of mixtures and a colloidal system.This is compose of a large number of substances or elements ,none of which is unique to living matter ,that is , these chemicals are also distributed in all non-living matter of the world.However , in living matter , these chemical have combined in a special way that imparts quality of life to this matter .The quality of life inherent in the protoplasm are the ability of response to stimuli , the ability of growth and reproduction and, the ability of performing chemical process [chemically called metabolism] .Besides , it can utilize and trnasform energy .The quality of life described above are not found in the matter present in non -living objects . BIOLOGY Biology is the study of objects that are alive due to the presence of steady and dynamic protoplasm in them .Such objects are named as living objects ,living beings, or living organisms .In contrast to the living objects ,the non-living objects are not alive .Since the protoplasm is absent in them , they donot posess life. The objects belong to two basic types- animals and plants .Athird category of living objects , include a vast assemblage of microscopic living objects which donot fit nearly into either animal assemblage or plant assemblage . MAIN BRANCH OF BIOLOGY Biology is divided into animal biology ,also termed Zoology,plant biology, also termed botany and micro biology . Zoology or animal biology deals with animals ,whereas botany or plant biology deals with plants .Microbiology is the study of microscopic biolgy objects which are distinctly neither animals nor plants .This is further subdivided into bacteriology ,dealing with bacteria and virology , relating to virus . Basic Biological Concepts [1] Living objects or living organisms secures survival ,not merely of the individual but also of the species . [2] To secure survival , the organisms are adapted to the environment , that is their structures and physiology fits them to live sucessfully in their particular situation .Every organism is adapted to its environment to lesser or greater extent; if this were not so , it would perish. [3] The greater variety of life forms , thaat is , biological objects have been arisen process of slow gradual change from simpler forms that existed in the geological past.In short, we find a progression from the simple to complex forms.

NATURE;MANIFESTATION OF MATTER AND ENERGY

2011-08-19T03:51:00.000-07:00

It is usually thought that nature is just our immediate surrounding .However, the nature is must vast because it includes whole universe which is composed of innumerable star sytems and all inter stellar spaces ,containig countless things .Every thing of the nature , small or large ,solid,liquid or gas ,living or non- living ,is composed of matter or matters. The matter undergoes change in the nature and the process affecting the changes invoves energy and its conversion . Matter ;If we have to understand the nature and functioning of the living matter , we must know something about its chemical nature and the process affecting the changes involves energy and its conversion .Anything that occupies space and has mass, is called a matter . The matter may assume solid ,liquid or gas state .For example , water is a liquid state , ice is its solid state and steam is its gas state. State of a matter depends on the prevailing temperature .Water ,for example,is liquid or gas state .State of a matter depends on the prevailing temperature .Water , for example, is liquid within temperature range of above0 degree to 10 degree c.Below this range it forms steam [water vapours] and is a gas.However ,regardless of the state in which it exists ,it has the same chemical composition ,h2o .This is true with all matters . Type and composition of a matter. A matter may be an element ,compound or mixture .An element is akind of matter which cannot be broken down into two or more different kinds of atoms .Iron , sulphur, calcium , iodine oxygen and hydrogen are typical examples of elements . Elements are commonly indicated by their abbreviation called chemical symbols [eg] Fe for the iron ,S for sulphur ,Ca for calcium ,Ifor iodine ] .Any of these elements can be broken down into smalest divisible unit called atom .This unit holds all the chemical characteristics of its element . Thus , atom is the building block of an element . More than 100 types of atoms are known .Therefore there more than 100 elements . An element has a sub atomic structure which is which is composed of electrically charged particles of three kinds,electron ,proton and neutron .The electro is negatively charged , proton positively charged and neutraon uncharged [neutral] .The number of proton is equal to the number of electrons in an atom of an element .An atom has a central part called nucleus which is surrounded by orbit[s] or circle[s] .The proton and neutron are presented in the nucleus but the electrons are present in orbit[s] ,revolving round the nucleus The number of proton ,neutron , and electron is fixed for every element ;some element may lack neutron , for example hydrogen[H] .The hydrogen has one electron in the orbit and one protons in the nucleus which lacks neutron .The hydrogen represent the simplest atom . There is another atom, allied to hydrogen atom ,called heavy hydrogen or deuterium .Like hydrogen ,its atom has one proton in nucleus and one electron in orbit but its nucleus also contains one neutron .There fore , it [deuterium] is heavier than hydrogen.

SCIENCE

2011-08-19T02:37:00.000-07:00

Science is an orderly and systematized body of knowledge based on observations, reasoning and experimental verification .The term Science has been derived from a Greek verb ,scire , meaning to know and latin noun scientia, meaning knowledge. The scientific knowledge is gatherd by observations ,inquiry and investigation .The main thing that distinguishes a science from the ''humanities'' , such as art an literature, is the use of experiments to answer questions. There is nothing mysterious about scientific reasoning or experiments. They are merely logical ways of trying to solved problems as are used by business people , historians and each of us in everyday life.We do not need specialized scientific training or knowledge to decide whether conclusions are justified from the data presented .We can requests further tests of atheory that does not appear to be well supported by evidence , and we can agree or dis agree with predictions from a theory . Significance of Science Science has assumed a great importance in modern society .Discoveries and inventions of science are inseperable from human life an welfare . Their application in day today problems provides solution for them . Many decisions on such subject as population control ,pollution standards , protection of wildlife and immunization .The body of scientific knowledge is already so vast that everyone cannot understand it all .However ,as a responsible citizen , we can follow some studies that bear on public issues .By doing so, we can apply scientific reasoning to decide our own positions on these issues. Ramification of Science When we use the term 'Science' without a descriptive adjective , we usually refer to a natural science which deals with natural phenomena ,in contrast to social science , such as sociology , which deals with human relations ,or an abstract science, such as mathematics , which deals with abstract relations or an abstract science ,such as mathematics ,which deals with abstract relations. The natural sciences are classified as physical sciences and biolgical sciences . The physical sciences primarily deal with non-living matterand include subject as physics , chemistry geology and astronomy. The biological sciences relate to living matters , living subject or living matters , living subjects or living organisms. Scientific Method Knowledge , imparted by any science , include facts, laws and principle of nature .The knowledge about thias is acquired by a typical procedure which is sometimes called scientific method or method of science Sequence of steps of this procedure are broadly classified as [1] observation [2] hypothesis[3] experimentation[4] conclusion and sometimes [5] resting.

ECONOMICAL IMPORTANCEOF WILDLIFFE

2011-08-19T01:42:00.000-07:00

The wildlife of a country is an important natural wealth of that country .If it conserved and exploited scientifically , it will earn a great revenue , leading to the economic growth of the related country .The exploitation of the wildlife for earning revenue can be done in the following ways ;

    [1] By scientific exploitation of feathers, skin , meat , horns ,etc., and exporting them to countries where they are in demand and to fetch high price .Thus , a huge foreign exchange can be earned through the wild life attracts tourists from different countries and thus it constitute a great source of revenue .The propely managed wild life can be developed into a revenue earning industry .The properly managed wildlife can be   developed into a revenue earning industry .The big game reserves of african countries attract many tourists .Fishing and shoting are important sources of income locally in many developed countries [2] Many species of widanimals are productive than domesticated livestock in their natural eco-systems. The se can be managed as a resource for human to utilise . [3] The collection of live wild animals for zoological gardens and dead wild animals is a good source of earning forign exchange .Besides , ity also serves as an effective sorce of knowledge for children and youngsters . Cultural and Aesthetic importance ; Mythological and children stories , told in many countries ,are mostly based on wild animals ,otherwise these would have been dull and infective .The circular dance of peacock with its fully expanded brilliantly coloured wings raised as a a large circular-disc is very fascinating .Songs of the birds infuse happiness and cheerfulness in us . If forest are deprived of wild animals,these would appear blank and boring inspite of their attractive grrenary .The wild animals of a country , particularly unique ones ,are national heritage of the country .                           IMPORTANT WILD ANIMALS OF INDIA                             [1] Lion ; Indian lion is very important and rare animal .It is regarded as national animal of our country and therefore ,finds place in our national emblem
[2] Tiger; Tiger live in a variety of habitats from horn forests to dense terai forests. In the Himalayas , they are found upto 2000 m height above sea level with wide distribution in uttar pradesh .                                [3] Panther ;The panther ,named tendua in hindi , is mostly tiger -like but smaller and spotted .It can live anywhere and prey upon   any animal ,even man. Therefore,it is more dangerous than tiger . [4]Hunting leopard or Cheetah; It is found on high mountains of the central India and preys upon swamp deers and their cubs .[5] Indian rhino or ghenda . About 5000 yrs ago rhino [rhinocerous ] was found in large number in plains of the indus river . Somehow , rhino disappeared gradually from the west and now are confined to grasslands and jungle areas of the foot hills of the himalayas and some part of bihar, bengal and assam .
                               Thus there is highly economical importances of wild animals so we have to save them .

WILDLIFE AND CONSERVATION

2011-08-19T00:41:00.000-07:00

Numerous animals and plants living in their natural habitats ,free from human check or interference ,are very important part of the treasure of wildlife in a country .In fact, the wild life is assemblage of such animals and plants .The non -domesticated mammals and birds living in there natural habitats are regarded as wildlifeanimals and their assemblage in a country is called animal wildlife of that country .India is gifted with very rich wildlife because of different eco-system and varying climatic condition therein .The royal bengal tiger ,lion ,elephant , buffalo, different kind of deers and huge assemblage of different kind of birds are considered to be natural wealth of this country. Plants, growing and flourishing in their natiral habitats ,are also important part of the wildlife and like wild animals ,these are also regarded as the natural wealth .However , this chapter will deal only with the wildlifeanimals. IMPORTANCE OF WILDLIFE The wildlife is greatly significant ot our existence and well being .It is important in many respects and its importance can be mainly classified as biological importance , economic importance , and cultural and aesthetic importance . Biological importance; The wildlife is very imprtant component of the nature .It maintains balance balance of different balance of different eco-systems of the nature through food chains .If this balance is disturbed or lost , unfavourable results will follow and these will eventually affect the life of man adversely.In a heterotrophic food chain , if one level is upset ,the other level will flourish at a tremendous rate ,and finally in want of natural food, these will prey upon valuable crops or man .This may be illustrated by an example of afood chain which include deers,antelops ,etc., as primary consumers and tigers,leopards ,wolves ,etc., as secondary consumers .In this food chain if primary consumers fall short in number ,the secondary consumers [tigers,leopards,wolves,etc] will prey upon domestic animals and tereafter if the domesticated animals fall short in number , the above mentioned secondary consumers will consume vegetables and crops raised or cultivated by farmers .Not only this ,they may also turn into man eaters s.This prey and predator chain maintains the balance of the nature .Obviously , the destruction of wild life will endanger our civilization . Bird act as pollinators , cause dispersal of fruits and seeds ,devour abnoxious insect pests or of crops and behave as sca vengers. If these or their habitats are destroyed ,the man will suffer and immense loss.

BLOOD PRESSURE

2011-08-18T23:50:00.000-07:00

The force of the strength of the jerk with which blood flows in blood vessels is called blood pressure .The source of this pressure is strong rythemic contraction of the heart . This force is sufficient for moving the blood from heart to organs through arteries and then from organs to heart through veins . The blood pressure in arteries is more than that in veins .The blood pressure is of two types ;systolic blood pressure and diastolic blood pressure .When heart contracts ,the artery has high blood pressure .This blood pressure is called systolic blood pressure But whe heart relaxes , the artery has reduced or less blood pressure called diastolic blood pressure .The blood pressure is measured by an instrument called sphygmomanometer .It depends upon the upon mental and physical conditions and age .Among young men the systolic blood pressure ranges from 100-140 mm Hg and the diastolic blod pressure fromm 55-80 mm Hg .The systolic pressure is is 90 plus age + 10 .Sometimes ,the blood pressure becomes high or low to the normal level .The high blood pressure develops due to unbalanced diet ,or heavy work ,or mental tension [anxiety ,worry an emotion ] or in old age because the diameter of arteries is reduced .Therefore, heart has to use more force for moving blood to organs .This may lead to heart failure . The low blood pressure develops due to fatigue and reduction in blood volume .There fore heart propels blood in arteries with less force. Consequently , body organs donot get nutrients and other substances in adequate quantities .Therfore , body becomes weak and this may lead to heart failure . Control of Body Heat By Blood All the invertebrates and lower vertebrates animals like fish , amphibia and reptiles are poikilothermic,that is , thier body temperature varies with that of thei surroundings .The temperature of such animal is usually a few degrees above that of its environment , but a rise or fall in the temperature of the air or water in which it lives will produce acorresponding change in the animal's body temperature .These animals produce heat but thy have very little capacity for conserving it or for adjusting supply and demand . Since the speed of most chemical changes that takes place in living organisms increased by a rise in temperature , it follow that the rate of activity of a poikilothermic animal will depend to a large extent on the surrounding temperature ; in cold conditions their low body temperature slows down all chemical changes and reduces the organism to a state of inactivity . Insects can be immobilized by a sudden fall of temperature . The quality of homiothermic condition is restricted to birds and mammals and means the ability ok keeping the temperature of the body constant, day and night , year in and year out Take your own example .A certain amount of heat is always produced by oxidation .Human muscles are about 40 % efficient as mechanical machines .This means that about 40% of energy produced by a muscle is available for machanical work and the other 60% appears as heat .the heat produced in cotracting muscle cells warms the blood in the surrounding capilaries .The warm warm blood transfers the heat to cooler tissues through which it passes .This is much like the distribution of heat by a hot water system Birds and mammals produce considerable amount of heat which is well distributed by the rapid circulating blood .This ,plus the mechanism for excreting excess heat, makes it possible for them to maintain a constant temperature of the body.

BLOOD

2011-08-18T23:01:00.000-07:00

The blood is a liquid connective tissue ,consisting of a liquid part called plasma and a cellular or solid part called formed elements ,consisting of blood cells or blood corpuscles .It is a dynamic connective tissue which adjusts its composition continuosly according to need of the body . PLASMA ;It is a whole blood minus formed element [blood corpuscles and blood platelets] , and can be separated from the whole body by centrifugation .If it is left to stand , it coagulates , forming a gel-like matter and a clear fluid called serum .The serum is similar to the plasma excepts that is lack coagulation factors .The plasma, atransparent ,alkaline and yellow fluid is composed of about 90% water and about 10% solid and it contributes to about 55% of the blood volume .The solid part of the plasma consists of proteins , inorganic salts and other substances such as glucose , amino acids , urea , enzymes ,hormones, anti bodies , oxygen ,carbon -dioxide , etc. The inorganic constituents of the plasma are Na,K,CL,HCO3, CA,etc. The main plasma proteins include albumin , globulin and fibrinogen which are large molecules and cannot pass through the thin wall of the blood capillaries.These proteins contribute mostly to the osmotic pressure of the plasma .Besides ,these also help to buffer changes in the blood acidity [ph] .The albumin is most abundants and the plasma proteins and accounts for the most osmotic pressure of the plasma .It checks excess loss of fliud from the blood .It also help many substance dissolved in the plasma by binding to them .Thus it plays important role in plasma transport .The globulin exists as alpha , beta and gamma globulins . the gamma globulins are antibodies which are involved in the immunological defence of the body.The alpha and beta globulins contribute to the osmotic pressure of the blood and also seve as carrier for substances.The fibrinogen, produced in the liver , serves as foundation of the coagulation of the blood during which it gets converted into insoluble fibrins as a networks of fibres . Blood corpuscles or blood cells ; The formed element of the blood are represent by blood corpuscles which are of three basic types ,the erythrocytes[=red blood corpusles , or red blood cells written as RBCin the abbreviated form] ,Leucocytes [=whitwe blood corpuscles or cells written as WBC in the abbreviate form] . Red blood cells [RBC] These blood cells are called erythrocytes are very small ,circular , bicon cave and dislike , about 8 u in diameter and 2u in thicknesss .Their bicon cave area provides more surface area , favouring more diffusion in and out .These4 are pliable elastic cells that bend , flex and twist while passing through tiny vehicles the cappilaries In mammals ,including man except camel and limma , the mature red blood cells lacks nucleus ,i.e., it is not nucleated .The red blood cells contain haemoglobin which gets more spaces for its accomodation in them due to absence of the nucleus .The individual red blood cells are pale yellow but when aggregated ,these appear reddish.The outer surface of the RBC has plasma membrane compose of lecithin nad cholesterol .This membrane enclose a homogenos matrix called stroma .containing loosely arranged network of fibrous and globular proteins which form the cyto skeleton .This is attached to the inner surface of the plasma membrane and gives disc-like shape to the RBC .However , other other cell organelles are absent due to absence of the nucleus .The stroma contain haemoglobin which gives pale red colour to the cell .Each erythrocyte has 200 to 300 molecules of the haemoglobin accounting fo the one- third of its volume .

RABBIT;CIRCULATORY SYSTEM

2011-08-18T22:14:00.000-07:00

The circulatory system is the transport system of the body,it transports various substances from tissues to tissues .Besides ,it maintains the chemical composition and physical environment of the body fluids ,essential for the metabolic reactions on which the life wheels on smoothly .Moreover , in certain animals such as birds and mammals ,it also it also maintains a body temperature to a constant level. The circulatory system of vertebrates , including mammal fall under two categories ,[1] blood vascular system and [2] lymphatic system .These are distinguishable on the basis of the circulatory or transporting medium; it is blood in the blood vascular system and lymph in the lymphatic system .However , the remarkable fact about the circulatory system of mammals is that it is of closed type i.e., the circulatory medium flows in vessels; even the lymph does not flow in open spaces within the body. 1.BLOOD VASCULAR SYSTEM ;The blood vascular system of the rabbit or any other mammal ,like that of other vertebrates , consists of the rabbit of higher muscular and highly contractile heart ,blood vessels,pervading every part of the body and blood vessels due to the pumping action of the heart . HEART The heart of the rabbit and other mammals, including man ,lies in the mediastinal space between the lungs ,inclined slightly to the left,.It is somewhat pear -shaped with broad -base ,lying toward the trachea ,and a narrow apex ,lying toward the diaph ragm .The heart is covered by the pericardium which is composed of two thin membranes between which is present a lymph like fluid called pericardial fluid .This fluid ensures free movement of the heart and absorbs shocks which oterwise may hurt the heart . External Structure ; The heart is extenally distinguishable into a broad anterior part called atrial or auricular part and a poterior narrow part called ventricular part .These two parts are demarcated by a transverse shallow groove like coronary sulcus which is placed far forward ,making the auricular part smaller than the ventricular part .The auricular part consists of the right and left auricles .Like wise , the ventri cular is also divided into the right and left auricles .Likewise , the ventricular part is also divided into the left and right ventricles by a logitudinal sulcus which starts from the base of the ventricular part , almost medially and extends backward obliquely toward the right not reaching the apex and therefore the left ventricle is large than the right ventricle . The sinus venosus and trunkus arteriosus are not found in the heart of the rabbit or any other mammal .The sinus venosus is merged into the right auricle and is represanted only by the sinu - auricular node[sanode] . Likewise , the trunkus arteriosus is completely merged in the left ventricle .The right auricle recieves venous or deoxygeneted blood from all parts of the body , except lungs by two superior vena cavae [anteroir vaena cavae or precavals ] and an inferior vena cava [= posterior vena cavae or postcaval ], whereas the left auricles recieves ithe oxygeneted blood from lung by two pulmanary veins The aorotid arches arise from the ventricles ; the pulmonary aorta arises from the right ventricle and the caratico- systemic aorta from the left ventricle .The pulmonary aorta and caratico -systemic aorta are joined by a liga ment called ligamentum arteriosus . The blood supply of the heart is maintain by acoronary artery and a coronery vein .

ABSORPTION OF DIGESTED FOOD

2011-08-18T03:11:00.000-07:00

While within the alimentary canal the food ,strictly speaking , is still outside the body .In order to be use to organism ,it most be absorbed in the blood stream .The entry of the digested food from the lumen of the gut ,specially intestine , into the blood stream is called absorption . Very little absorption takes place either in the buccal cavity or in the stomach but these can be scarcely classified as food .By far the greater part of the absorption takes place in the ileum .The food is in a very soluble and easily diffusible form and hence it can be easiy absorbed throug its wall into the blood and lymph cappilaries . The absorptive area of the small intestine is enormously increased by the development of villi in this region .In man ther are 5,000,000 minute waving villi , providing a very large inner surface area [5 times the body surface ] for absorption .Each villus is wellsupplied with the capillary blood vessels and lacteals are concerned with the absorption of fat .The oval peyer's patches or lymphoid nodules manufacture certain white corpuscles known as lymphocytes which also helps in the absorption of fat .The vermiform appendix which has the structure of peyer's patches is also absrptive in a high degree. The digested carbohydrates chiefly as glucose and protein must pass through where it break up into cappilaries .Thus all the carbohydrates chiefly as glucose and proteins as amino acids are observed into the villus cappilaries and lead to the factor of the hepatic portal vein .The hepatic portal vein passes into the liver where it break up into capillaries .Thus all the carbohydrates and proteins must pass through the liver before entering to the general circulation .In this respect the liver provides a very important regulatory mechanism .Any exccess of blood sugar is always changed into glucose and stored in liver cells .On the other hand , if there is shortage of sugar in the blood , the glycogen stored in the liver is turned once again into glucose by and enzyme known as glycogenase and released into the blood .In this way the liver not only acts as a regulator but also as a store house of carbohydrates . The amino acids are brought by the hepatic vein to the liver and are allowed to go into the general circulation. Thecells of the body absorb amino acids are dealt with in the liver ; by a complex actions the amino acids are split up. The carbon , hydrogen and oxygen unite to form glycogen or fat and the nitrogen forms ammonia .Ammonia is highly poisonous and is not released into the blood in any quantity in mammals .It combines with carbon dioxide under the influence of certain enzymes to form urea .The breaking down of amino acids is known as deamination. The digested fat , as fatty acids and glycerol , passes directly into the lacteals where it is at once changed into minute droplet of fat so that this vessels contain a milky white emulsion .The removal from the intestinal contents of the digested carbohydrates ,proteins and fats leaves afluid residue containing undigested and indigestable food , remais of bacteria and largely of undigested cellulose .This residue passes into the caecum and colon where further process of absorption takes place but it is chiefly of water .A largely proportion of water is absorbed during the passage of this fluid residue through the colon so that by the time it reaches the rectum the residue becomes semi-solid and form the faeces , which is thrown out at intervals.

INGESTION AND DIGESTION

2011-08-18T00:52:00.000-07:00

[The account of the digestion presented under this section is applicable to maost mamals including man ] .As his already been stated , the rabbit gnaws its food.By means of chisel-shaped incisors , small portion of the vegetables matter are cut up and after being caught by the mobile lips are taken into the buccal cavity .Here the food is throughly mixed with saliva and subjecte to the action of the grinding cheek-teeth .During later process which is called mastication , the food is turned round and round in the buccal cavity by movements of the tongue and chhek -muscles until the whole forms a pulpy mass..Through mastication is of very great importance in herbivores animals like rabbit which live entirely on vegetable matter containing a great deal of starch.It should be noted that in such animals the molar and pre-molar have special transverse ridges for grinding the food . Further the surfaces of the tongue is hard and helps by rubbing the food against the palatine ridges on the roof of the mouth cavity. . When mastication is completed , the pulpy mass is swallowed .This is affected by the bonus being pushed into pharynx by the raising of the tongue, prevented from entering the posterior nares by the soft palate and isa finally forced into the beginning of the oesophagus by the contraction of the pharyngeal wall.During the contraction of the pharynx and entry of the bolus into the oeso phagus the food is prevented from entering into the larynx through the glottis by a flap- like epiglottis .The oeso phagus conveys the food to the stomach through the activity of the layer s of the muscles in its walls.This activity causes peristalsis . The first stages in the conversaion of food into the protoplasm of the animal is its partial breaking down into simpler compounds . In all cases the digestion consists of a process of hydro lysis,during which the molecular size of the subsances is progressively reduced until the true sollution is possible .These changes are brought about by the familiar biocatalysts known as enzymes or ferments. Inmouth , the food comes in contact with the colourless wateryfluid or saliva , secreted in the mouth cavity by the front pairs of salivary glands , which keeps the mouth continuosly moist under normal conditions.When the food is in mouth ,its smell and tastes considerably increase the rates of its secretion .Since food stays for a very short time in a mouth , it is not in the mouth but in the stomach where thwe main bulk of the salivary digestion takes place Besides ptyalin ,saliva contains 99% water ,mucin albumin ,globumin ,etc.The function of saliva are as follows ; 1 It changes insoluble starch and glycogen into soluble maltose . 2; It helps in swallowing and moistening and lubricating the food.3 It dissolves soluble substance and thus make them fit for tasting .4It has a cleaning effect on the mouth and the teeth . In the mouth ,3-5 percent of the carbohydrates are digested in the suceeding part of the alimentry canal . The digestion doesnot takes place in the oeso phagus because the oeso phagus secretly only mucin ; it doesnot produce any digestive enzyme .The mucin is simply added to the bolus so that it easily passes from the oesophagus to the stomach .However . the action of the ptyalin , which has already started in the mouth , continues . Digestive in the stomach . The food is subjected to the action of the gastric juice , secreted by the tubular gastric glands .As soon as the food reaches the stomach ,its wall is mechanically simulated to produce the gastrin harmone , which , in turn stimulates gastric glands to pour gastric juice into the lume of the stomach The gastric juice is composed of water , mucin ,hci an three digestive enzymes such as pepsin ,rennin [in young ones of rabbit and calves of cattles] and gastric lipase The mucin protects the tissue from the action of enzymes .It is amphoteric [a substance that can act as both acid and base according to conditions] in nature and can thus nutralises both acids and alkalies besides providing a mechanical buffer between hard food substance and the living tissues