What causes the movement of food inside the alimentary canal?

Plants have low energy needs as compared to animals. Explain.

Lack of oxygen in muscles often leads to cramps among cricketers. This results due to

How many chambers are present in the heart of fishes? How many times does blood flow through the heart during each cycle?

$(a)$ How many chambers are present in the heart of $(i)$ fish $(ii)$ amphibians? $(b)$ Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?

Which is the first enzyme to mix with food in the digestive tract?