Exchanging substances

• The lungs' job is to transfer oxygen to blood and remove waste carbon dioxide from it. They contain alveoli where gas exchange occurs.
• Blue is blood with carbon dioxide

  Red is blood with oxygen
• Alveoli are specialised to maximise the diffusion of oxygen and carbon dioxide through their

  • large surface area
  • moist lining for dissolving gases
  • very thin walls
  • good blood supply
• The inside of the small intestine is covered in villi. They increase surface area so digested food is absorbed into the blood quicker.
• Villi have a

  • single layer of surface cells
  • very good blood supply to assist quick absorption
• Gills have a large surface area for gas exchange. Each gill is made up of lots of tiny gill filaments covered in lamellae which

  • increase surface area
  • have lots of blood capillaries to speed up diffusion
  • have a thin surface area
• The concentration of oxygen in water is always higher then that in the blood
• The underneath of a leaf is covered in stomata which carbon dioxide passes through
• Oxygen and water vapour diffuse out of the stomata
• Stomata size are controlled by guard cells which close if the plant is losing water faster then wanted
• Flattened shape of a leaf increases exchange surface area
• Cell walls have air spaces inside to increase surface area.