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
Gas exchange takes place in the alveoli
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
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
Digested food
moves into the
blood by diffusion
and by active
transport