Which of the following is NOT a function of enzymes in the smooth endoplasmic reticulum?

A. The cells will shrink at first, but will later reach equilibrium with the surrounding solution and return to their original condition: If the solute cannot cross the membrane, the cells cannot regain water through solute equilibration, so they will not return to their original size.

B. The cells will show no change due to diffusion of both solute and solvent: In a hypertonic solution where the solute is impermeable, only water can move, so diffusion of solute does not occur and the cell will be affected by water loss.

C. The cells will lose water and shrink: Water moves out of the cell by osmosis to balance the higher extracellular solute concentration. The loss of water causes the cells to shrink, a process called crenation.

D. The cells will swell and ultimately burst: Swelling occurs in a hypotonic solution where water enters the cell due to lower solute concentration outside. In a hypertonic solution, the opposite occurs, so bursting does not happen.

A. Chloride ions: Chloride ions help stabilize the membrane potential by balancing charges, but they move passively along gradients set by other ions. Since chloride permeability is not the dominant factor at rest, they do not primarily determine the resting membrane potential.

B. Calcium ions: Calcium concentration is kept very low inside cells compared to outside. Its main role is in processes like muscle contraction and neurotransmitter release, rather than in establishing the electrical gradient at rest, so it contributes little to resting potential.

C. Potassium ions: Potassium ions are the major determinant of resting membrane potential because the membrane is most permeable to potassium at rest. Efflux of potassium through leak channels leaves the inside more negative, making it the primary driver of resting potential.

D. Sodium ions: Sodium ions are more concentrated outside the cell and tend to diffuse inward, but the membrane has low sodium permeability at rest. Although sodium influx is important during depolarization, it is not the chief factor in establishing resting membrane potential.