Name the red pigment which carries oxygen in the blood.

What is meant by the terms 'single circulation' and 'double circulation'?

Describe the working of human blood circulatory system with the help of a suitable diagram which shows all the steps involved.

Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

How many chambers are there in the heart of: (i) an amphibian, (ii) a mammal, and (iii) a fish?