Give reasons for the following:
(a) Arteries are thick walled.
(b) Blood goes only once through the heart in fishes.
(c ) Plants have low energy needs.

Explanation

(a) Arteries ar thick walled because these vessels carry blood from the heart to all the part of the body and blood emerges from the heart under high pressure.
(b) A fish has a two chambered heart and has gills to oxygenate blood. In a fish, the heart pumps deoxygenated blood to gills where oxygenation of blood takes place. The oxygenated blood from the gills is supplied to the body part of the fish where oxygen is utilised and carbon dioxide enters into it, making it deoxygenated. This deoxygenated blood returns to the heart to be pumped into gills again. Thus blood passes through the heart of fish only once in one complete cycle.
(c) Plants are fixed at a place and do not show any locomotion. Plants are less active. Their cells do not need to be supplied with materials so quickly. Therefore plants have low energy needs and respire at a slow rate.