The insect circulatory fluid is called what?

• A. Hemolymph
• B. Blood
• C. Lymph
• D. Plasma

Answer: (A)

Insects use an open circulatory system, so the circulating fluid is called hemolymph. This fluid bathes all tissues in the body cavity (the hemocoel) and functions as the transport medium for nutrients, hormones, and wastes, as well as a medium for immune cells. It’s pumped by the dorsal heart and flows through body spaces rather than remaining strictly inside closed vessels. Because it isn’t the same as vertebrate blood and doesn’t form a separate plasma component within a closed vascular system, the correct term is hemolymph.

Blood refers to the circulating fluid of vertebrates that is contained within vessels and includes plasma, red and white cells, and platelets. Lymph is a tissue fluid in vertebrates that drains from tissues into lymphatic vessels and eventually the bloodstream. Plasma is the liquid component of vertebrate blood, containing dissolved proteins and solutes. These terms describe fluids in different circulatory contexts, whereas insects rely on hemolymph for their circulatory needs.