Crossing Membranes Passive Processes

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Crossing Membranes 1 – Passive Processes

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Diffusion

The After Shave Man

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Diffusion in Air

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Diffusion in water

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What is diffusion? (definition)

Diffusion is the movement of molecules (or ions) from a region of high concentration to a region of lower concentration until they are spread out evenly

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Example 1:Diffusion in the Alveoli: O2 diffusing into the blood and CO2 diffusing out of the blood

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Example 2: Some digested food diffuses across the gut wall into the blood

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What affects the rate of diffusion?

Concentration gradient: The greater the difference in the concentration of a substance in two areas, the faster the rate of diffusion

The rate of diffusion is directly proportional to the concentration gradient

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What affects the rate of diffusion?

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Small particles tend to diffuse faster than larger ones

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Diffusion takes place more quickly through thin membranes (e.g. exchange of gases through the alveolar wall)

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The larger the surface area the higher the rate of diffusion (e.g. in gases diffusing into/out of leaves)

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The shorter the distance, the faster the rate of diffusion

An increase in temperature

increases the rate of diffusion

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Facilitated Diffusion

Faster movement

Cell membrane proteins used

Channel proteins

Carrier proteins

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Channel Proteins facilitate the diffusion of Ions

Na+

K+

Ca2+

Cl-

Why can ions not diffuse freely across the membrane?