Question

a. diffusion is the net movement of molecules from an area of (low/high) concentration to an area of (low/high) concentration.
b. the molecules will continue to move along this (semi - permeable membrane/concentration gradient) until they reach (diffusion/equilibrium).
c. once equilibrium is reached, molecules will continue to move across a membrane (randomly/in one direction).

Explanation:

a. Diffusion is the net movement of molecules from an area of high concentration to an area of low concentration. This is because molecules tend to spread out to fill available space.
b. Molecules move along the concentration gradient (difference in concentration) until equilibrium (equal concentration throughout) is reached. A semi - permeable membrane is a structure, not what the molecules move along in the context of the concentration - related movement described here.
c. Once equilibrium is reached, molecules continue to move randomly. There is no net movement in one direction as the concentrations are equal.

Answer:

a. high; low
b. concentration gradient; equilibrium
c. randomly