Question

select the true statements. molecules diffuse across a cell membrane until they are all on one side. molecules move down their concentration gradient to reach equilibrium. once equilibrium is reached, molecules stop crossing the cell membrane. equilibrium is reached when molecules have an equal concentration on both sides of the cell membrane.

Explanation:

• Molecules diffuse across a cell membrane until they are all on one side: This is incorrect. Diffusion continues until equilibrium (equal concentration on both sides) is reached, not all on one side.
• Molecules move down their concentration gradient to reach equilibrium: Correct. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration (down the concentration gradient) until equilibrium.
• Once equilibrium is reached, molecules stop crossing the cell membrane: Incorrect. At equilibrium, molecules continue to move across the membrane, but there is no net movement (equal movement in both directions).
• Equilibrium is reached when molecules have an equal concentration on both sides of the cell membrane: Correct. By definition, equilibrium in diffusion means equal concentration on both sides.

Answer:

Molecules move down their concentration gradient to reach equilibrium.
Equilibrium is reached when molecules have an equal concentration on both sides of the cell membrane.