specialised exchange systems

• exchange surfaces have special features to improve their efficiency such as a large surface area, they're thin and a good blood supply
• larger organisms have a greater metabolic rate
• a smaller surface area to volume ratio means disunion to internal cells would e
• • The cells on plant roots grow into long 'hairs' which stick out into the soil. Each branch of a root will be covered in millions of these microscopic hairs.
  • Gives the roots a large surface area, which helps to increase the rate of absorption of water by osmosis and mineral ions by active transport from the soil.
  • it has very thin walls so a very short diffusion distance
  • cell sap in root hairs contains dissolved sugar and minerals so water enters the root hairs very readily from the soil to increase the water potential
• Exchange surfaces are usually thin to decrease the distance that the substances being exchanged have to travel over, and so improve efficiency. Some are only one cell thick.
• • Each alveolus is made from a single layer of thin, flat cells called the alveolar epithelium.
  • Oxygen diffuses out of the alveolar space into the blood.
  • Carbon dioxide diffuses in the opposite direction.
  • The thin alveolar epithelium helps to decrease the distance over which oxygen and carbon dioxide diffusion takes place, which increases the rate of diffusion
  • the alveoli are surrounded by a large capillary network giving each alveolus its own blood supply
• • The alveoli are surrounded by a large capillary network, giving each alveolus its own blood supply. The blood constantly takes oxygen away from the alveoli, and brings more carbon dioxide.
  • The lungs are ventilated so the air in each alveolus is constantly replaced.
  • These features help to maintain concentration gradients of O2 and CO2
• • In the gills, O2 and CO2 are exchanged between the fish's blood and the surrounding water.
  • as the water passes through the openings between the sections of the gill the oxygen dissolved in the water diffuses into the gills and is taken into the blood
  • Fish gills contain a large network of capillaries - this keeps them well-supplied with blood.
  • They're also well-ventilated - fresh water constantly passes over them.
  • These features help to maintain a concentration gradient of O2 - increasing the rate at which O2 diffuses into the blood.