Diffusion through the cell membrane

I can explain why some substances can diffuse through the cell membrane and others cannot.

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Diffusion through the cell membrane

I can explain why some substances can diffuse through the cell membrane and others cannot.

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Key learning points

All substances, including the cell cytoplasm and substances within it, are made up of particles.
Particles of some substances diffuse into and out of a cell by moving through small holes in the cell membrane.
The particles that make up some substances are too big to diffuse through the holes in the cell membrane.
The cell membrane is selectively-permeable because only some substances can diffuse through it.
The net movement of particles through a cell membrane is down a concentration gradient.

Keywords

Cell membrane - All cells are surrounded by a membrane that controls what can enter and leave the cell.
Particles - All substances are made up of particles that are too small for us to see.
Diffusion - Diffusion is the net movement of particles of a substance down a concentration gradient.
Selectively-permeable - A material is selectively-permeable if some substances can move through it but others cannot.
Net movement - Net movement is the overall movement of particles from one area to another.

Common misconception

Thinking that all, or no, substances can diffuse through the cell membrane. Thinking that cells choose to take in particular substances, or that cells breathe or suck in substances such as oxygen.

The lesson explores the idea that particles of some, but not all, substances are small enough to diffuse through holes in the selectively-permeable cell membrane.

In Task A, students could be allowed to choose from a collection of objects which one they think is the best model of a cell membrane, or be asked to come up with their own suggestions and then peer assess their objects.

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Licence

This content is © Oak National Academy Limited (2025), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).