Question

What could be the possible explanation for the evolution of four-chambered heart in mammals as opposed to two-chambered heart in fishes?

• A. Fishes do not require energy to maintain their body temperature.
• B. Fishes have efficient gills.
• C. Mammals have more complex structure than fishes.
• D. Fishes can store more energy than mammals.

Answer 1

Answer: (A), (C)

Mammals have more complex structure than fishes.

In fishes, the heart is two-chambered and there is mixing of oxygenated and deoxygenated blood. They are cold blooded, so energy is required only for locomotion and hence less amount of oxygen is sufficient in them. Birds and mammals are warm blooded, so more energy is required to keep up the body temperature so, more oxygen supply is required. Therefore, the heart has four chambers and oxygenated blood and deoxygenated blood is kept strictly separated.