Final answer:
A closed circulatory system circulates blood within blood vessels, separate from the body fluid, with varying heart chambers across different species: two chambers in fish, three in amphibians and reptiles, and four in mammals and birds.
Step-by-step explanation:
A closed circulatory system is one in which the blood is entirely contained within a network of blood vessels and the heart, separate from the body's interstitial fluid. This system is highly efficient at transporting nutrients, gases, and wastes throughout the organism. In comparison, the heart structures within animals with closed circulatory systems differ significantly:
- Fish have a two-chambered heart, with one atrium and one ventricle, which leads to unidirectional circulation.
- Amphibians and most reptiles have a three-chambered heart, where there is some mixing of oxygenated and deoxygenated blood.
- Mammals and birds possess a four-chambered heart with two atria and two ventricles, allowing for complete separation of oxygenated and deoxygenated blood (double circulation).
It is crucial to note that b) provides the correct definition and description of the closed circulatory system and heart structure differences.