# Explain how the cell membrane controls the movement of substances into and out of a cell. In your answer, include reference to diffusion, osmosis and active transport.

> Eduqas A-Level Biology — 1.3 Cell membranes and transport · Explain · 5 marks

> Red blood cells are surrounded by blood plasma. The plasma contains glucose, oxygen, carbon dioxide and various salts at different concentrations to those inside the red blood cells.

## Mark scheme (5 marks)

1. The cell membrane is selectively permeable, allowing only certain substances to pass through
2. Diffusion is the movement of substances from a region of high concentration to a region of low concentration across the membrane
3. Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration across a selectively permeable membrane
4. Active transport moves substances from a region of low concentration to a region of high concentration (against the concentration gradient)
5. Active transport requires energy (from respiration), whereas diffusion and osmosis do not

## Key terms

- [cell membrane](https://www.gradenine.co.uk/glossary/cell-membrane)
- [diffusion](https://www.gradenine.co.uk/glossary/diffusion)
- [osmosis](https://www.gradenine.co.uk/glossary/osmosis)
- [active transport](https://www.gradenine.co.uk/glossary/active-transport)

## Related

- [Revision notes for Eduqas A-Level Biology](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-cell-membrane-controls-a52de74a) · Published by Druglandscape Ltd.