exchanging substances

• gas exchange in the lungs:

  lungs transfer oxygen to the blood and remove waste carbon dioxide

  for this the lungs contain alveoli (tiny air sacs where gas exchange takes place)
• alveoli are specialised for diffusion of 02 and c02, they have:

  1. a massive surface area
  2. a moist lining (for disolving gasses)
  3. very thin walls
  4. a good blood supply
• the small intestine insides are covered in tiny villi that hugely increase its surface area and allows digested food to quickly be absorbed into the blood, for this they have a single layer of surface cells and a good blood supply
• gas exchange in fish:

  water enters fishes mouths and leaves through the gills, in the gills the oxygen (from the water) diffuses into the blood and carbon dioxide (from the blood) diffuses into the water,

  gills are made up of gill fillaments that are covered in lamallae which increase the surface area.
• lamallaes adaptations:

  1. lots of blood capillaries
  2. a thin surface area (minimise the diffusion distance)
  3. blood and water flow in opposite directions to maintain a high concentration gradient
• adaptations in the leaf for easy diffusion:

  1. stomata
  2. flattened shape (increases area, more effective)
  3. walls of cells inside the leaf are exchange surfaces
• stomata are holes on the bottom of leaves that allow carbon dioxide to diffuse into leaves and oxygen and water vapor to diffuse out, they are controlled by guard cells that close the stomata when it is too hot or dry and too much water is being lost.