In insects, how does the blood circulate?

• A. Flows around inside the body cavity with no closed circulatory system.
• B. Circulates through a closed network of arteries and veins with a heart and aorta.
• C. Moves only through dorsal vessels connected to the brain.
• D. Is pumped by gill-like organs for tissue delivery.

Answer: (A)

Insects have an open circulatory system, where the circulating fluid (hemolymph) is not confined to a closed set of vessels. The heart is a long dorsal vessel with ostia (openings) that pumps hemolymph into the body cavity (the hemocoel); the fluid then bathes the organs and tissues before slowly returning to the heart. Gas exchange is mainly handled by the tracheal system, not by the circulatory system, so the hemolymph isn’t the primary oxygen carrier. This is why the idea of a closed network of arteries and veins, or pumping by gill‑like organs, doesn’t fit insects.