Diffusion
Diffusion is the movement of particles from a region where they are in high concentration to a region where they are in low concentration, and is one of the ways substances can move across the cell membrane, into or out of the cell.
Particles diffuse down a The difference in the concentration of a chemical across a membrane.. This is known as This is the movement of molecules down a concentration gradient without the need for additional energy, eg diffusion and osmosis..
Image caption, Diffusion experiment
Potassium permanganate is placed into a beaker of water
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Examples of diffusion in living organisms
Products of digestion, dissolved in water, can pass across the wall of the small intestine by diffusion. Their concentration is higher in the small intestine than their concentration in the blood, so there is a concentration gradient from the intestine to the blood.
Oxygen and carbon dioxide, dissolved in water, are exchanged by diffusion in the lungs:
- oxygen moves down a concentration gradient from the air in the Tiny air sacs in the lungs, where gas is exchanged during breathing. to the blood
- carbon dioxide moves down a concentration gradient from the blood to the air in the alveoli
The dissolved substances will only continue to diffuse while there is a concentration gradient.
Blood flow continuously takes oxygen away from the lungs. This helps to maintain the concentration gradient.