Question
Explain the evolution of heart from fishes to mammals.
✓
Answer
- (1) Fishes:
- They have only two chambered heart, one atrium and lower ventricle.
- The blood is pumped to the gills, which is oxygenated there, and passes directly to the rest of the body.
- Thus, blood goes only once through the heart in the fish during one cycle of passage through the body.
- (2) Amphibians and many reptiles:
- Amphibians and most of the reptiles are cold blooded.
- Therefore, they can tolerate mixing of oxygenated and deoxygenated blood.
- They have three chambered hearts which mix the oxygenated and deoxygenated blood.
- (3) Birds and mammals:
- They have four chambered hearts.
- The complete seperation of the right and the left side of the heart is keeps oxygenated and deoxygenated blood separate without mixing.
- Such separation allows a highly efficient supply of oxygen to the body.
- This is useful in animals as they have high energy needs for to maintain their body temperature.
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