Exchange surfaces

• A single-celled organism has a relatively large surface area:volume ratio
• The tissues of a multicellular organism consist of cells with a similar structure and function. Organs, such as the heart and lungs, are made of tissues.
• One organ may consist of several tissues. Organ systems, such as the circulatory system, are groups of organs that perform a particular function.
• In multicellular organisms many organ systems are specialised for exchanging materials. The effectiveness of an exchange surface is increased by: • having a large surface area • a membrane that is thin, to provide a short diffusion path • (in animals) having an efficient blood supply • (in animals, for gaseous exchange) being ventilated