Question

what is the difference in the concentration of molecules in two areas across a membrane?
a concentration gradient
b equilibrium
c diffusion
d active transport

Explanation:

To solve this, we analyze each option:

• Option a: A concentration gradient is defined as the difference in the concentration of molecules between two areas across a membrane. This matches the question's description.
• Option b: Equilibrium is when the concentration of molecules is equal across the membrane, so there's no difference. Eliminate.
• Option c: Diffusion is the movement of molecules from an area of high to low concentration (down a gradient), not the difference itself. Eliminate.
• Option d: Active transport is the movement of molecules against a concentration gradient using energy, not the concentration difference. Eliminate.

Answer:

a. concentration gradient