AP BIOLOGY

Detailed explanation-1: -Answer and Explanation: The correct answer is option C. Endocytosis is a form of active transport. Endocytosis is the biological process wherein molecules in the extracellular environment are taken in by the cell.

Detailed explanation-2: -The four main kinds of passive transport are simple diffusion, facilitated diffusion, filtration, and/or osmosis.

Detailed explanation-3: -A concentration gradient occurs when the concentration of particles is higher in one area than another. In passive transport, particles will diffuse down a concentration gradient, from areas of higher concentration to areas of lower concentration, until they are evenly spaced.