Multiple Choice Question Why does active transport require energy to move molecules of a substance across a cell membrane? A. Lack of the substance makes the cell weak. B. The substance moves from low to high concentration, against the concentration gradient. C. The cell membrane is very thick. D. The substance moves from high to low concentration, with the concentration gradient.

Answer 1

The correct answer is: B. The substance moves from low to high concentration, against the concentration gradient.

Active transport requires energy because it involves moving molecules against their concentration gradient, which means moving them from an area of lower concentration to an area of higher concentration.