CBSE Class 10 Answered

Fishes show single circulation whereas birds and mammals show double circulation. This means that in fishes, blood goes only once through the heart during one cycle of passage through the body. In birds and mammals, blood flows twice through the heart, during each cycle of passage through the body.

Fishes have only 2 chambers in their hearts, whereas birds and mammals show 4 chambers.

In fishes, blood is pumped from heart to gills, where it is oxygenated. After oxygenation, it passes directly to the rest of the body. In birds and mammals, blood is pumped from heart to lungs for oxygenation. But after oxygenation, the blood is again taken to the left side of the heart from where it is pumped to the rest of the body.

Double circulation prevents mixing of oxygenated and deoxygenated blood and keeps them separate. Thisis not achieved by single circulation.

Double circulation provides highly efficient supply of oxygen to the body. This is useful in endothermic animals like mammals and birds, having high energy needs.

Another advantage of double circulation over the single circulatory system is that for each circulation the blood has to pass through only one set of capillary networks before returning to the heart. This helps to maintain a higher blood pressure and a higher speed of flow of the blood. In turn this helps to maintain steeper diffusion gradients than in animals with single circulation and so the exchange of metabolites (oxygen etc.) is more efficient.