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Diffusion, Osmosis, Active Transport

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Additional Notes

Diffusion: movement of molecules, from a region of high concentration to a region of low concentration.

- Oxygen diffuses into cells, and the waste carbon dioxide diffuses out.

Osmosis: movement of water molecules, across a partially permeable membrane, from a region of high concentration of water to a low concentration of water molecules.

- It allows plants to take in water through their roots.
- It is used in kidney dialysis machines to filter the blood.

Semi-permeable membrane

- Small molecules, such as water can pass through the small holes in the membrane…
- But larger molecules like sugar cannot pass through the membrane.


A and B are salt solutions. A has a concentration of 2 g/cm3 and B has a concentration of 3 g/cm3

a) Describe solutions A and B using the terms ‘hypotonic’, ‘hypertonic’ or ‘isotonic’.

Solution A is hypotonic relative to B.

or solution B is hypertonic relative to A


b) Describe solutions A and B in terms of water potential

Solution A has a higher water potential than solution B

or Solution B has a lower water potential than solution A


c) Describe solutions A and B in terms of concentration

Solution A is less concentrated/more dilute than solution B

Solution B is more concentrated/less dilute than solution A