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 .