# Explain how the resting membrane potential of a neuron is maintained.

> IB DP Biology Standard Level (2023 syllabus) — C2.2 Neural signalling · Explain · 4 marks

## Mark scheme (4 marks)

1. The resting membrane potential is approximately −70 mV (inside negative relative to outside).
2. Sodium–potassium (Na⁺/K⁺) pumps actively transport 3 Na⁺ out of the cell and 2 K⁺ into the cell per cycle, using ATP.
3. The membrane is more permeable to K⁺ than to Na⁺ at rest (through leak channels), so K⁺ diffuses out down its concentration gradient.
4. The net outward movement of positive charge (K⁺ leaving) and the unequal pump ratio leave an excess of negative charges inside, establishing the negative resting potential.

## Key terms

- [resting membrane potential](https://www.gradenine.co.uk/glossary/resting-membrane-potential)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-resting-membrane-potential-afcf46d8) · Published by Druglandscape Ltd.