AP BIOLOGY

Detailed explanation-1: -It takes place across a biological membrane where a transporter protein couples the movement of an electrochemical ion (typically Na+ or H+) down its electrochemical gradient to the upward movement of another molecule or an ion against a concentration or electrochemical gradient.

Detailed explanation-2: -During active transport, substances move against the concentration gradient, from an area of low concentration to an area of high concentration. This process is “active” because it requires the use of energy (usually in the form of ATP).

Detailed explanation-3: -Active transport is the movement of molecules across a cell membrane in the direction against their concentration gradient, going from a low concentration to a high concentration.

Detailed explanation-4: -When a cell expands energy to move a solute across its membrane against a concentration gradient, this process is called active transport. Active transport is a movement of substances from lower to higher concentration and requires cellular energy to achieve this movement.

Detailed explanation-5: -Answer and Explanation: The movement of a substance across a biological membrane against its concentration gradient with the help of energy input is active transport, which is option b.