AP BIOLOGY

Detailed explanation-1: -Active transport: moving against a gradient To move substances against a concentration or electrochemical gradient, a cell must use energy. Active transport mechanisms do just this, expending energy (often in the form of ATP) to maintain the right concentrations of ions and molecules in living cells.

Detailed explanation-2: -Active transport requires energy for the process by transporting molecules against a concentration or electrochemical gradient.

Detailed explanation-3: -Diffusion is the movement of particles from high concentration to low concentration in a substance. This process is essential for life on Earth, allowing for the movement of molecular compounds into and out of the cell.

Detailed explanation-4: -Passive transport requires no energy input, as compounds are able to move freely across the membrane based only on a favourable concentration gradient (Figure 1.11).