What term is used to describe the transport medium or 'blood' in insects?

The term used to describe the transport medium or 'blood' in insects is haemolymph. In the insect circulatory system, haemolymph plays a crucial role similar to that of blood in vertebrates. It circulates throughout the body, transporting nutrients, hormones, and waste products. Unlike blood, which contains red blood cells and hemoglobin for oxygen transport in vertebrates, haemolymph is a clear or yellowish fluid that does not carry oxygen in the same manner.

Haemolymph is also important for other functions, including temperature regulation, nutrient storage, and defense against pathogens. The open circulatory system of insects allows haemolymph to flow freely within the body cavity, bathing the internal organs and tissues directly. This system is different from the closed circulatory systems found in mammals, where blood is confined to vessels.

The other terms listed describe components associated with the circulatory systems of vertebrates. Hemoglobin is a protein specifically involved in oxygen transport in vertebrate blood. Plasma and serum are components of blood in vertebrates; plasma is the liquid part of the blood that carries cells and nutrients, while serum is the fluid that remains after blood coagulation. These terms do not apply to insects, reinforcing the uniqueness of haemolymph