Refer to the Two Figures Below

Multiple Choice

Refer to the two figures below. The figures show the interaction of the same human muscle cell with oxygen and carbon dioxide.Which statement is correct and supported by these figures?

A) When a substance is present at a high concentration outside of a cell, the substance diffuses into the cell, but when a substance builds up inside a cell, it must be pumped out.
B) The arrows in the two figures indicate that molecules move in only one direction and never in the opposite direction during diffusion.
C) Once the concentrations of a substance are equal on both sides of the membrane, particles stop moving and diffusion stops.
D) Diffusion across the cell membrane occurs in cases of small nonpolar molecules and involves a net movement of molecules in the direction from high to low concentration.
E) Diffusion of substances across a cell membrane differs from diffusion of substances in solution in that equilibrium is achieved only in the case of the cell membrane.