Biology 3 (i)

Gaseous exchange happens in the lungs.

The job of the lungs is to transfer oxygen to the blood and to remove waste carbon dioxide from it.

To do this the lungs contain millions of little air sacs called alveoli where gaseous exchange takes place.

The alveoli are specialised to maximise the diffusion of oxgen and CO2. They have: 

• An enormous surface area (about 75m  in humans)
• A moist lining for dissolving gases
• Very thin walls
• A copious blood supply

Villi

the inside of the small intestine is covered in millions and millions of tiny little projections called villi.

They increase the surface area in a big way so that digested food is absorbed much more quickly into the blood.

They have:

• A single layer of surface cells
• A very good blood supply to assist quick absorption