The concentration of sodium on the inside of the cell is 20 mM. The outside of the cell has a sodium concentration of 115 mM. Which mechanism of ion uptake would best move sodium from the inside of the cell to the outside?

Sodium would move from a concentration of 20 mM inside the cell to 115 mM outside, where its concentration is higher. Moving an ion against its concentration gradient requires energy, so active transport is the best mechanism. Diffusion and passive transport move substances down their concentration gradients, while osmosis refers to water movement.

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