Explain why the cell membrane is important for controlling what enters and leaves a cell.

Edexcel GCSE Biology (1BI0) — 1.1 Cell biology · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

All living cells are surrounded by a cell membrane. The cell membrane is described as selectively permeable.

Model answer (4 marks)

The cell membrane is selectively permeable, allowing only certain substances to pass through. This lets useful molecules such as glucose and oxygen enter the cell while keeping harmful substances out. It also permits waste products like carbon dioxide or urea to leave. By controlling the movement of materials, the membrane maintains a stable internal environment and keeps the cell functioning correctly.

Examiner tips

Use the term "selectively permeable" early. Show the two directions: entry of nutrients and exit of waste. Mention the result: stable internal environment. Keep answer concise to fit 4 marks.

Common mistakes

Confusing the membrane with the cell wall. Failing to mention both entry of nutrients and exit of waste. Using vague phrases like "helps the cell" without explaining the mechanism.

Mark scheme (4 marks)

The cell membrane is selectively permeable, meaning it allows some substances to pass through but not others
This allows useful substances such as glucose and oxygen to enter the cell
Waste products such as carbon dioxide or urea can leave the cell
This maintains a stable internal environment / prevents harmful substances from entering the cell, keeping the cell functioning correctly

Key terms in this question

cell membrane