AP BIOLOGY

Detailed explanation-1: -The potassium ion channel of bacteria is a beautiful example of passive transport in which ions move down a concentration gradient. However, many important transport systems function to move molecules against a concentration gradient. This is known as active transport (Figure 8).

Detailed explanation-2: -1: Passive Transport: Diffusion is a type of passive transport. Diffusion through a permeable membrane moves a substance from an area of high concentration (extracellular fluid, in this case) down its concentration gradient (into the cytoplasm).

Detailed explanation-3: -Passive transport, most commonly by diffusion, occurs along a concentration gradient from high to low concentration.

Detailed explanation-4: -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-5: -If movement is with the concentration or gradient, it is passive. If movement is against the gradient, it is active and requires energy.