Q67 of 167 Page 211

There are five animals A, B, C, D and E. The animal A uses its modified forelimbs for flying. The animal B uses its forelimbs for running whereas the animal C uses its forelimbs for grasping. The animal D can live on land as well as in water and uses its forelimbs to prop up the front end of its body when at rest. The animal E which respires by using spiracles and tracheae uses wings for flying but its wings are analogous to the modified forelimbs of animal A.

(a) What could the animals A, B, C, D and E be?


(b) Why are the forelimbs of animals A, B, C and D called homologous organs ?


(c) What does the existence of homologous organs in animals A, B, C and D tell us about their ancestors?


(d) Why are the modified forelimbs of animal A and the wings of animal E called analogous organs?


(e) State whether animals A and E have a common ancestor or not.

(a)Animals A, B, C, D and E could be sparrow, Lizard, human, frog, insect.

(b) Forelimbs of Bird, lizard, human and frog are called homologous organs because their basic structure of bones is similar but they perform different functions. This means that they have had a common ancestor and with time they adapted themselves according to the requirements.


(c) The existence of homologous organs in animals A, B, C, D tell us that since they have similar basic structure of origin, they have a common ancestor.


(d) Modified forelimbs of Bird and wings of Insect are called analogous organs because they have different basic structure but they perform similar functions. Bird uses its forelimbs to fly; similarly insect uses its wings to fly. Because their basic structure of origin is different so they do not have a common ancestor.


(e) No, Animals having analogous organs do not have a common ancestor because their basic structure of origin is different.


More from this chapter

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65

Some of the important fossils which have been studied are those of organisms X, Y and Z. X were marine arthropods which were common between 400 to 600 million years ago. Y were the invertebrate animals (molluscs) with a flat, coiled, spiral shell which lived in the sea about 180 million years ago. Z are the extinct carnivorous or herbivorous reptiles which appeared on the earth about 250 million years ago and became extinct about 65 million years ago. What are X, Y and Z?

 66

The farmers have been cultivating a food plant X for over two thousand years and have produced as many as five entirely different looking vegetables A, B, C, D and E from it.

(a) What could the plant X be?


(b) What are A, B, C, D and E?


(c) What is the process of evolution involved in this example known as?

 68

X, Y, and Z are three animals. The animal X can fly but animal Y can only run on ground or walls. The forelimbs of animals X and Y have the same basic design but they are used for different purposes such as flying and running respectively. The animal Z became extinct a long time ago. The study of fossils of Z tells us that it had some features like those of X and some like those of Y. In fact, Z is said to form a connecting link in the evolutionary chain of X and Y.

(a) What could the animals X, Y and Z be?


(b) What name is given to the forelimbs like those of X and Y which have the same basic design but different functions?


(c) Name one feature in which Z resembled X.


(d) Name one feature in which Z resembled Y.


(e) Which is the correct evolutionary chain involving X, Y and Z: X Z Y or YZ X?

 69

A population of red beetles lives in green bushes in a garden. Once during the process of breeding, a green beetle is produced.

(a) State whether the change in color of beetle is a process of evolution or not.


(b) Can the new color of green beetle be passed on to its next generations?


(c) What will be the advantage (if any) of the green color to the beetle?


(d) State whether the production of green color involved a change in genetic material or not.