How useful is the study of the nature of body cavity and coelom in the classification of animals?


Coelom is the body cavity which is lined by a mesoderm. The presence or absence of body cavity or coelom plays a very important role in the classification of animals.
Animals that having  a cavity between body wall and digestive tract are known as coelomates for eg. annelids, molluscs, arthropods, echinodermates, and chordates etc.
The animals in which the body cavity is not lined by mesoderm are known as pseudocoelomates. In such animals, mesoderm is scattered in between ectoderm and endoderm. Aschelminthes is an example of pseudocoelomates.
Animals in which the body cavity is absent  are known as acoelomates For e.g platyhelminthes.



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If you are given a specimen, what are the steps that you would follow to classify it?


The steps that we would follow to classify the given specimen will be
(i) First we would classify the specimen according to the level of organisation. The animals can be classified into Cellular and Tissue/Organ level.

(ii)  The second criteria for classification would be on the basis of the body symmetry i.e. whether the specimen is of radial symmetry of bilateral symmetry.

(iii) The third classification would be on the basis of the body cavity or coelom.  Wheteher the body cavity is present or absent. And whether the coelom  is acoelom, pseudocoelom or true coelom
     
(iv) The specimen would be classified on the basis of the arrangement or the number of the layers into diploblastic or triploblastic.

(v) The specimen would then be classified on the basis of the presence or the absence of notochord.










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Could the number of eggs or young ones produced by an oviparous and viviparous mother be equal? Why?


The numbers of eggs produced by an oviparous mother will always be more than the young ones produced by a viviparous mother. This is because in oviparous animals, the development of young ones takes place outside the mother's body. Thus, their eggs are vulnerable because of the harsh environmental conditions and predators. Therefore, to overcome the loss, more eggs are produced by mothers so that even under harsh environmental conditions, some eggs are able to survive and produce young ones.
On the other hand, in viviparous organisms, the development of young ones takes place inside the body of the mother. Since the development takes place inside the body the young one is less exposed to environmental conditions and predators. Therefore, there are more chances of their survival and hence, less number of young ones is produced compared to the number of eggs.

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Ravi’s younger brother of class III stated that bats are like birds as they are able to fly.
How will you contradict him and make him understand that bats are mammals and not birds?


Flight is not only the criteria for classifying bat as birds. The features that bat has which prove that it is a mammal and not a bird are:

i. External ears

ii. Body covered with hairs and mammary glands. 

iii. They have skin instead of feathers and mouth.

iv. They have teeth instead of the beak.

v. They do not lay eggs but give birth to young ones.

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What are the modifications that are observed in birds that help them fly?


Birds have undergone many structural adaptations to suit their aerial life. Some of these adaptations are as follows:
(i) Streamlined body for rapid and smooth movement and to counter the resistance offered by the air current.
(ii) Covering of feathers for insulation.
(iii) Forelimbs modified into wings and hind limbs used for walking, perching, and swimming.
(iv) Presence of pneumatic bones to reduce weight.
(v) Presence of additional air sacs to supplement respiration.
(vi) Endoskeleton has hollow long bones to reduce weight that favors flying.
(vii) Uricotelic excretion that helps to reduce storage of water to reduce weight.

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