B3 - Diffusion through cell membranes

B3 - Diffusion through cell membranes

1. Gas exchange happens in the lungs

   • The job of the lungs is to transfer oxygen to the blood and to remove waste CO2 from it. To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place

2. Gas exchange takes place in the alveoli

3. The alveoli are specialised to maximise diffusion of O2 and CO2. They have an enormous surface area, a moist lining for dissolving gases, very thin walls, a good blood supply

4. The villi provide a really big surface area

   • The inside of the small intestine is covered in millions of tiny projections called villi. They increase the surface area 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

5. Digested food moves into the blood by diffusion and by active transport