B3 -Diffusion through cell membranes

Gas exchange happens in the lungs
1. Lungs job is to transfer oxygen to the blood and to remove waste carbon dioxide from it.
  1. To do this the lungs contain millions of little air sacs called alveoli where gas exchange takes place.
Alveoli are specialised to maximise diffusion of oxygen and CO2. They have an enormous surface area (75m2), a moist lining for dissolving gases, very thin walls, a ood blood supply.
The inside of the small intestine is covered in millions of tiny projections called villi. They increase surface area in a big way so that digested food is absorbed much more quickly into the blood.
1. They have a single layer of surface cells and a vey good blood suplly to assist quick absorption.

Resource summary

	Created by Lily O'Brien almost 8 years ago