true or false? during diffusion, substances enter a cell against the concentration gradient.

The statement "during diffusion, substances enter a cell against the concentration gradient" is false. Diffusion is a passive process where substances move from an area of higher concentration to an area of lower concentration, meaning they move down or along the concentration gradient. Substances do not naturally move against the concentration gradient during diffusion. Moving substances against the concentration gradient—i.e., from low to high concentration—requires energy and occurs through active transport, not diffusion. Active transport uses energy, such as ATP, to pump molecules against the concentration gradient into or out of cells. Therefore, during diffusion, substances always move into a cell down the concentration gradient, not against it.