# Explain how the sodium–potassium pump (Na⁺/K⁺-ATPase) maintains the electrochemical gradient across the plasma membrane of an animal cell.

> IB DP Biology Higher Level (2023 syllabus) — B2.1 Membranes and membrane transport · Explain · 4 marks

## Mark scheme (4 marks)

1. The pump is a transmembrane (integral) protein that uses ATP hydrolysis to drive active transport against concentration gradients.
2. Three sodium ions are pumped out of the cell per cycle, raising extracellular Na⁺ concentration and lowering intracellular Na⁺ concentration.
3. Two potassium ions are pumped into the cell per cycle, raising intracellular K⁺ concentration relative to the extracellular fluid.
4. Because three positive charges leave but only two enter per cycle, the pump generates a net negative charge inside the cell, contributing to the electrical component (membrane potential) of the electrochemical gradient.

## Key terms

- [Na⁺/K⁺-ATPase](https://www.gradenine.co.uk/glossary/na-k-atpase)
- [electrochemical gradient](https://www.gradenine.co.uk/glossary/electrochemical-gradient)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](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/explain-how-the-sodium-potassium-pump-na-k-atpase-8570c66c) · Published by Druglandscape Ltd.