topic 1 - exchanging substances

• gas exchange -

  happens in the lungs when oxygen is transferred to the blood and removal of carbon dioxide.Lungs have millions of air sacs called aveoli which is where gas exchange takes place
• Alveoli is specialise to maximise the diffusion rate of oxygen and carbon
• alveoli functions -

  enormous surface area

  moist lining

  very thin walls

  good blood supply
• Small intestines is filled with millions of projections called villi, which increase surface area
• Villi have single layer surface area and good blood supply to assist quick absorption
• gills are the gas exchange surface in fish
• water enter the fish via the mouth and passes out through the gils.Oxygen diffuses from the blood in the gills and carbon dioxide diffuses from the blood into the water