If we inspect most cell membranes in a living human body, we would find a nearly continuous flow of substances back and forth across the plasma membrane. Which of the following explains this continuous flow?
A) Cell metabolism is constantly using up oxygen and raw materials; this lowers their concentration, so more will diffuse into the cell.
B) Cell metabolism is constantly producing waste molecules; this increases their concentration, so more will diffuse into the cell.
C) Cells produce useful secretions; this increases their concentration, and more will diffuse into the cell.
D) Cell metabolism constantly produces oxygen in respiration; this increases the cell's affinity for carbon dioxide which diffuses into the cell.
E) Cells are non-living and therefore anything can pass in and out of the cell.

Question

Quizplus · Accepted Answer

Cell metabolism constantly uses up oxygen and raw materials, which lowers their concentration, creating a concentration gradient. As a result, more of these substances will diffuse into the cell to balance the gradient. Additionally, waste molecules may also diffuse out of the cell in order to maintain equilibrium. This results in a continuous flow of substances across the plasma membrane.

If We Inspect Most Cell Membranes in a Living Human