# The cell membrane is described as selectively permeable and controls the movement of substances into and out of the cell. Explain how the structure and properties of the cell membrane allow it to carry out this function, and describe two ways in which substances can move across the cell membrane.

> WJEC A-Level Biology (Wales) — 1.3 Cell membranes and transport · Explain · 5 marks

> Cells need to take in useful substances such as glucose and oxygen, and remove waste products such as carbon dioxide. The cell membrane plays a key role in controlling this movement.

## Mark scheme (5 marks)

1. The cell membrane is selectively permeable, meaning it only allows certain substances to pass through
2. The cell membrane has receptor molecules on its surface for cell-to-cell signalling
3. Diffusion — substances move from an area of high concentration to an area of low concentration across the membrane
4. Osmosis — water moves across the selectively permeable membrane from a region of high water concentration to a region of low water concentration
5. Active transport — substances are moved against the concentration gradient (from low to high concentration) using energy

## Key terms

- [cell membrane](https://www.gradenine.co.uk/glossary/cell-membrane)
- [selectively permeable](https://www.gradenine.co.uk/glossary/selectively-permeable)

## Related

- [Revision notes for WJEC A-Level Biology (Wales)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/the-cell-membrane-is-described-as-0af01602) · Published by Druglandscape Ltd.