AP BIOLOGY

Detailed explanation-1: -Primary active transport directly uses a source of chemical energy (e.g., ATP) to move molecules across a membrane against their gradient.

Detailed explanation-2: -Facilitated diffusion therefore allows polar and charged molecules, such as carbohydrates, amino acids, nucleosides, and ions, to cross the plasma membrane. Two classes of proteins that mediate facilitated diffusion are generally distinguished: carrier proteins and channel proteins.

Detailed explanation-3: -The active transport of small molecules or ions across a cell membrane is generally carried out by transport proteins that are found in the membrane. Larger molecules such as starch can also be actively transported across the cell membrane by processes called endocytosis and exocytosis.

Detailed explanation-4: -During active transport, a protein pump uses energy, in the form of ATP, to move molecules from an area of low concentration to an area of high concentration. An example of active transport is the sodium-potassium pump, which moves sodium ions to the outside of the cell and potassium ions to the inside of the cell.