AP BIOLOGY

Detailed explanation-1: -Why does osmosis occur in cells? Water moves through a semipermeable membrane in osmosis because there is a concentration gradient across the membrane of solute and solvent. The solute cannot effectively move to balance the concentration on both sides of the membrane, so water moves to achieve this balance.

Detailed explanation-2: -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-3: -Answers. FACILITATED DIFFUSION. In facilitated diffusion, substances move into or out of cells down their concentration gradient through protein channels in the cell membrane. Simple diffusion and facilitated diffusion are similar in that both involve movement down the concentration gradient.

Detailed explanation-4: -A semipermeable membrane allows only solvent molecules to pass through while leaving behind solute molecules. Such type of diffusion of water through a semi-permeable membrane is called osmosis.

Detailed explanation-5: -Cell membranes serve as barriers and gatekeepers. They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot.