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the spreading of the particles of a gas, or of any substance in solution, resulting in a net movement from a region where they are of a higher concentration to a region with a lower concentration

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When does it occur?

occurs spontaneously due to the random movement of fluid particles - all gas, liquid or dissolved particles have kinetic energy of movement

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Greater the difference in concentration, the...

the faster the rate of diffusion, due to the steeper concentration gradient

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How big are the molecules?

Only relatively small molecules can diffuse through cell membranes eg amino acids but not proteins, sugars like glucose but not large carbohydrate molecules like starch

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Oxygen and Respiration

oxygen required for respiration passes through cell membranes by diffusion.

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Where does it occur?

Diffusion occurs in all mixtures of gases, liquids or solutions.

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Anything dissolved in a solution can...

spread or diffuse if there is a difference in concentration ie a net transfer of the substance from one place to another eg through a cell membrane

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