The study of the functional properties of insect tissues and organs. Insects are one of the most diverse groups of animals on Earth. They have evolved adaptations that allow them to live in a variety of ecosystems. The basic body plan comprises a hard exoskeleton forming a protective covering over internal tissues. The interior of the exoskeleton is referred to as the hemocoel. Insects have an open circulatory system with hemolymph (blood) freely moving within the hemocoel and bathing all of the internal tissues. A basement membrane composed of a noncellular matrix of proteins, lipids, and carbohydrates separates the internal tissues from the hemolymph. The fat body is a specialized tissue within the hemocoel. It is usually a whitish tissue found throughout the body of the insect and is involved in storing fat reserves. It is also involved in general metabolism and regulates the composition of the hemolymph. The fat body is, in fact, the site of production for the major proteins found in the hemolymph.