Diffusion

Diffusion

1. Villi in the small intestine

   • wall just one cell thick - ensures that there is only a short distance for absorption to happen by diffusion and active transport.
   • Increased surface area to absorb more nutrients.

2. Gas exchange in the lungs

   • Large surface area - many alveoli are present in the lungs with a shape that further increases surface area.
   • Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance.
   • Extensive blood supply - ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs
   • A large diffusion gradient - breathing ensures that the oxygen concentration in the alveoli is higher than in the capillaries so oxygen moves from the alveoli to the blood. Carbon dioxide diffuses in the opposite direction.

3. gills of fish

   • large surface area of the gills
   • large surface area of the blood capillaries in each gill filament
   • the short distance required for diffusion – the outer layer of the gill filaments and the capillary walls are just one cell thick
   • there is a counter current flow of water and blood

4. roots and leaves in plants

   • large surface area
   • Thin leaves minimize the diffusion pathway

5. Amoeba

   • large surface area
   • Thin cell membrane to create a thinner diffusion pathway