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Diffusion

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Diffusion is the NET movement of a substance down its concentration gradient.

Increasing the rate of diffusionEdit

  • Distance - a shorter distance will increase the rate of diffusion. This is why the walls of the alveoli and capillaries are so thin.
  • Concentration gradient - A greater concentration gradient will mean the rate of diffusion increases. This concentration gradient is kept large by removing the substance as it moves across the place where it diffuses.
  • Size of molecules - smaller is quicker
  • Surface area - a greater surface area is better for fast diffusion. There are many alveoli in the lung and therefore have a very large surface area.
  • Temperature - since molecules have a greater kinetic energy at a higher temperature and will therefore diffuse quicker



Definition of Diffusion- Diffusion is the movement of a substance from an area of high concentration to an area of low concentration this is called the concentration gradient.

Diffusion and living organismsEdit

Diffusion is very important to all living organisms.

Diffusion of oxygen from alveoli to red blood cellsEdit

There are thousands of tiny air sacs (alveoli) in humans' lungs, around which are wrapped tiny capillaries. Inside these capillaries are many red blood cells. Oxygen molecules move randomly around inside the alveoli . Some move through the cell wall of the alveolus and then through the capillary wall. Since there are a lot of oxygen molecules inside the alveoli and not many inside the red blood cells; therefore the net movement of oxygen is from the alveoli to the blood. The oxygen has moved down a concentration gradient by diffusion.

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