Exchanging substances

• gas exchange happens in the lungs
• the alveoli are where gas exchange takes place
• oxygen diffuses from high concentration to low concentration, so it moves into the bloodstream
• carbon dioxide is produced by cells during respiration, which means that there's more carbon dioxide inside the body than outside
• how are alveoli specialised?

  large surface area

  moist lining

  thin walls

  good blood supply
• villi increase the surface area of the small intestine so that digested food is absorbed quickly into the blood
• structure of leaves let gasses diffuse in and out of the cells
• the bottom of a leaf has many holes called stomata which allow gases to pass through
• oxygen and water vapour is diffused out of the stomata
• the size of the stomata is controlled by the guard cells. these close if the plant needs to retain water
• gills have a large surface area for

  gas exchange