specialised exchange surfaces

• Diffusion is the movement of particles from a high concentration to a low concentration
• Osmosis is movement of water through a partially permeable membrane from a high water potential (dilute solution) to a low water potential (concentrated solution).
• Active transport is the movement of particles across a partially permeable membrane from a low concentration to a high concentration
• The higher the temperature the faster the rate of diffusion because the particles have more thermal/ kinetic energy and so move faster
• Rate of diffusion is inversely proportional to membrane thickness
• The surface area and the volume of a sphere are calculated using 4πr2 and 4/3 πr3 respectively and this is useful because the alveoli in the lungs are one of the main (gas) exchange surfaces in the human body and these air sacs are sphere-shaped
• • As a an animal gets larger it’s surface area: volume ratio gets smaller.
  • The bigger something gets on the outside it must get even bigger on the inside to allow it to function
  • E.g. there is comparatively much more volume inside an elephant than a mouse, because it is a lot bigger. This means that it has a much lower surface area compared with it’s volume.
• To be efficient a gas exchange surface must:

  • have a large surface area.
  • be supplied with lots of blood vessels to take gases away – maintains concentration gradient.
  • be moist so gases can dissolve for diffusion.
  • be very thin so diffusion across the membrane is easy.
  • have a concentration gradient i.e. keep the air circulating
• explain how the alveoli are adapted

  • The walls of the alveoli are thin so that gases can diffuse easily/ efficiently/ more quickly.
  • Oxygen diffuses from the lungs into the blood
  • Diffusion is when the oxygen moves from a high concentration to a low concentration
  • Alveoli increase the surface area of the lungs
  • A large surface area will increase the rate of diffusion.
  • A good blood supply around the alveoli maintains the concentration gradient of these gases.
  • Good ventilation in the alveoli will maintain the concentration gradient.
  • It is moist to allow quicker/more efficient diffusion
• Explain how a fish’s gills are adapted for gas exchange - Large surface area, good blood supply to maintain concentration gradient, thin membranes to reduce diffusion distance.
• Explain how a root hair cell is adapted to its function -

  Large surface area, thin membranes to reduce diffusion distance
• Explain how the small intestine is adapted to its function - Villi and microvilli increase surface area, good blood supply maintains the concentration gradient, thin membranes  reduce diffusion distance
• The Peruvian screaming toad does not have gills and has a very simple lung with no alveoli. Explain how it gets enough oxygen to survive -

  It has thin moist skin which allows gases to diffuse through it over a large surface area. It has blood vessels near the surface of the skin to maintain the concentration gradient
• Explain why an elephant has large ears -

  To create a large surface area to radiate heat away efficiently and keep the elephant cool