AP BIOLOGY

Detailed explanation-1: -In passive transport, no energy is needed in order for molecules to move across the membrane. Diffusion across a cell membrane works best with large, complex molecules. Different from passive transport because it requires energy. Active transport is necessary to make particles move against their natural tendency.

Detailed explanation-2: -Only the smallest molecules like water, carbon dioxide, and oxygen can freely diffuse across cell membranes. Larger molecules or charged molecules often require an input of energy to be transported into the cell. Even when equilibrium is reached, particles do not stop moving across the cell membrane.

Detailed explanation-3: -Diffusion is the movement of molecules from an area of high concentration of the molecules to an area with a lower concentration. For cell transport, diffusion is the movement of small molecules across the cell membrane.

Detailed explanation-4: -If a cell is a single-celled microorganism, such as an amoeba, it can satisfy all of its nutrient and waste needs through diffusion. If the cell is too large, then diffusion is ineffective at completing all of these tasks.

Detailed explanation-5: -Large polar or ionic molecules, which are hydrophilic, cannot easily cross the phospholipid bilayer. Charged atoms or molecules of any size cannot cross the cell membrane via simple diffusion as the charges are repelled by the hydrophobic tails in the interior of the phospholipid bilayer.