Why must cells pump out extra ions

If sodium ions are outside of a cell, they will tend to move into the cell based on both their concentration gradient and the voltage across the membrane (the more negative charge on the inside of the membrane). So cells pump out the extra ions.

This is what my candidate teacher said..

If the sodium ions are outside a cell, they would have to move the cell depending on its concentration gradient and the voltage across the membrane (the more negative charge within the membrane). So the cells pump the extra ions.

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explanation:

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