This week you learned that each animal phylum has its own unique organization of

Question

This week you learned that each animal phylum has its own unique organization of body structures, or body plan. The body plan includes levels of organization (cells -> tissues -> organs -> organ systems), body symmetry, differentiation of germ layers, cavity formation, patterns of embryological development, segmentation, cephalization, and limb formation. Compare and contrast the two different types of body symmetry, and name an example of each. Is one type advantageous over the other? Explain.

Explanation / Answer

Radial symmetry: a) In this kind of symmetry the body radiates outward from a central point.

b) They do not have a left or right side but have a top and bottom side.

c) It is suitable for sessile, slow moving or floating animals

Eg : Sea snemone, Jellyfish, Star fish

Bilateral symmetry:

a) In this kind of symmetry one single plane devides an animal body into two equal halves which are mirror image to each other.

b) It has both left and right side as well as a front and rear side

c) It is mostly found in moving animals.

Eg: almost 99% animals who are motile are bilaterally symmetric , for example mammals, birds, reptiles etc.

The bilateral symmetry is advantageous over radial symmetry because of a front and rear end. As during movement the front end confronts the environment 1st, all the sensory equipments are developed in the front end leaving the rear end only for faster movement. This also gives rise to cephalization at the front end. Due to perception of gravity the difference between dorsal and ventral also becomes prominant. This kind of symmetry gives a overall perception of the immidiate environment of an organism and thus makes movement easier and faster. Also bilateral symmetry produces a streamline body which reduces drag force thus helps movement in air or water easier.

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