BIOL 1107 Chapter Notes - Chapter 44: Gastrovascular Cavity, Extracellular Fluid, Hemolymph
Document Summary
Least complex animals (sponges, cnidarians, flatworms) have no distinct circulatory system. Aquatic or are surrounded by body fluids of a host animal. Bodies are structured as thin sheets of cells that lie close to the fluids of surrounding external environment. Substances diffuse between cells and environment through animal"s external surface or through surfaces of internal channels and cavities that are open to environment. Sponges- water carrying nutrients and oxygen is pumped by surface cells with beating flagella through pores in body wall surrounding central cavity. Passes through cavity and leaves through large exit pore (carrying co 2 and wastes) Gastrovascular cavity: saclike body cavity with single opening, mouth, which serves both digestive and circulatory functions. Large, complex animals- most cells lie in cell layers too deep within body to exchange substances directly with external environment by diffusion.
