How can substances be transported across a membrane against their concentration gradient?

To move substances against a concentration or electrochemical gradient, a cell must use energy.

Explanation:

This occurs because During active transport, substances move against the concentration gradient from an area of low concentration to an area of high concentration which is a  “active” progress which requires the use of energy (usually in the form of ATP). It is the opposite of passive transport.

answer; i believe the correct answer is (replication is not conservative);

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