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OCTOBER 25, 2012

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A major part of the Earth comprises living beings, which make up the biological world. There are millions of  unique varieties of plants and animals. All living beings are distinguished by their ability to move, respire, grow and reproduce, which are absent in non-living things.



Studying the millions of varieties is a Herculean task for any scientist. To achieve it, therefore, the scientists have grouped together similar types of plants / animals to simplify their study. By studying a representative of each group, we can know fairly well the unique features of the whole group. Such a system of grouping together living beings is known as classification.




Scientists in different parts of the world call the same animal / plant by different names. It may create a lot of problems in communication. To rid of this problem, a uniform system of naming has been proposed by Carl Von Linneaus. According to this system, every organism has been assigned two names


1. generic name known as genus and


2. a special name known as species. For instance, both the common cat and and the lion have a common genus Felis, but since there is considerable difference in their characters, each has a separate species name. Obviously, having a common genus name means great similarity in their basic biological features. The common names and the corresponding scientific names of some common living beings are elsewhere in this discussion.




         ANIMAL GROUPS                                                                PLANT GROUPS


1. Phylum Protozoa e.g. Amoeba, Plasmodium                    1. Algae e.g. Seaweeds, Spirogyra

                                                                                                     2. Fungi e.g. Penicillium


2. Phylum Porifera e.g. sponges                                             3. Bryophytes e.g. Marchantia


3. Phylum Coelentrata e.g. Corals, Jelly-fish, Star-fish         4. Pteridophytes e.g. Ferns


4. Phylum Platyhelminthess e.g. Tapeworm                          5. Gymnosperms e.g. Pinus


5. Phylum Nemahelminthes e.g. Ascaris                               6. Angiosperms e.g. Triticum


6. Phylum Insecta e.g. Silver Fish, Cockroaches


7. Phylum Echinodermata 


8. Phylum Mollusca


9. Phylum Chordata e.g. Rat, Whale, Fishes


(Bacteria and viruses are excluded because they possess the features of both plants and animals. For instance, some bacteria can make their own food, which brings them closer to plants. Viruses, on the other hand are creatures which can multiply only on a living host, can survive extreme environmental conditions and possess features of both living and non-lining beings. Like living beings, they can multiply. And like non-living things, they can crystallize themselves under appropriate environmental conditions. Many bacteria and viruses are responsible for some major human diseases.)


Of these, the Chordates are the most advanced group in terms of biological organization. They are distinguished by the presence of a notochord or vertebral column. They are further divided into many types.


A. Pisces (Swimming Fishes)   


B. Amphibia                


C. Reptilia (Crawling Reptiles)


D.  Aves (Flying Birds)            


E. Mammalia (Child-Bearing Mammals)



Each animal group is marked by certain features unique to them e.g.


1. Fish have gills for respiration in the adult stage, fins all over the body and internal fertilization. Therefore, swimming doesn’t define a fish nor does the name tag of fish attached to the name of an animal. For example, the commonly known animal Silver Fish is not fish at all (it is an insect), because it lacks gills, fins and other features exclusive to fishes.

2. Amphibians are animals that can live on both land and in water.  A typical example is a frog which lives in ponds normally, but can come on earth.


3. Reptiles have scales found all over the body. Since they live in dry places, it helps them in conserving body water to a large extent.


4. From birds onwards, a true four-chambered heart is found in all animals, which means that pure and impure blood are actually separated in different chambers of the heart. Birds have wings (which are actually modified fore-limbs) and a constant body temperature, apart from a four-chambered heart. Of course, they can fly, but the ability to fly does not make an animal a bird.  For instance, many insects can fly with wings that are extensions of the skin. So technically speaking, they cannot be called birds.


5. Mammals are the most advanced animal groups. Many features distinguish them other groups like


A.    The presence of hair all over the body.


B.    Internal fertilization (in groups, fertilization takes place outside the body, i.e. is external)


C.    Ability to give birth to young ones directly (birds and fishes lay eggs)


D.    A constant body temperature which does not change as per outside changes. Such constant-temperature animals are called warm-blooded while those whose body temperature changes with outside changes are called cold-blooded e.g. fish, reptiles.


E.    A constant internal temperature is a great advantage for an animal because it lets its body function without any hindrance (Most body processes need a suitable range of temperature). Its importance can be easily supported with frog, which is a cold-blooded animal. In winters when temperature dips very low, frogs bury themselves in the bed of the ponds (hibernation) to avoid the low temperature, which hinders their body functions. On the other hand, most mammals have internal biological mechanisms which adjust their temperature to avoid excessive heat or cold, thus creating a constant internal environment for the body reactions. (homeostasis)


Extreme care of the young is a special feature of this group. Generally speaking, the more advanced the animal on the scale, the more the degree of parental care. A highly developed Central Nervous System, which allows them to think, plan and reason, is an essential aspects of their intelligence. Of course, no animal apart from humans can speak but some remarkable research shows that chimpanzees can definitely communicate with special sign languages.


Common Name              Scientific Name


  Oryza sativa

Onion                                            Allium cepa

Pea                                               Lathyrus odoratus

Cat                                                Felis domesticus

Homo  sapiens

Frog                                               Rana tigrina


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