Cambridge O Level Biology · Syllabus 5090 · Human Gas Exchange
Gas Exchange Surface
What is Gas Exchange Surface?
A specialised region of an organism where gases are exchanged with the environment by diffusion. An efficient gas-exchange surface has a large surface area, so that many molecules can cross at once; a barrier only one or two cells thick, so that the diffusion distance is short; a moist lining, so that gases dissolve before they diffuse; a dense supply of blood or other transport medium, which removes the diffusing substance and so keeps the concentration gradient steep; and a means of renewing the medium on the other side, which in humans is ventilation. In humans the gas-exchange surface is the total surface of the alveoli in the lungs.
This definition is part of the Human Gas Exchange chapter in Cambridge O Level Biology.