MODERN CELL DOCTRINE

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

 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

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

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

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

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

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

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

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

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

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

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

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]

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

                       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

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

 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

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.