Biology 4.3 Exchange of Gases in the Lungs

Site of gas exchange in mammals = epithelium of alveoli.

Alveoli - minute air sacs 100-300um in diameter.

Essential features of exchange surfaces

• Large surface area to volume ratio - speeds up rate of exchange.
• Very thin - short diffusion pathway so materials can cross rapidly.
• Partially pemeable - selected materials diffuse through easily.
• Movement of environmental medium e.g. air - maintain a diffusion gradient.
• Movement of internal medium e.g. blood - maintain a diffusion gradient.

Diffusion is proportional to: (surface area x difference in concentration…