Question

which of the following statements about diffusion is correct?
it is very rapid over long distances.
it requires an expenditure of energy by the cell.
it is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
it is an active process in which molecules move from a region of lower concentration to one of higher concentration.
it is a passive process in which molecules move from a region of lower concentration to a region of higher concentration.

Explanation:

Diffusion is a passive process. In passive transport, no energy expenditure (like ATP) is required by the cell. Molecules in diffusion move down their concentration gradient (from higher to lower concentration).

• The first option is wrong because diffusion is slow over long distances (e.g., in large organisms, simple diffusion is not sufficient to supply all cells with nutrients over long distances, which is why circulatory systems exist in complex organisms).
• The second option is wrong as diffusion is passive (no energy expenditure by the cell).
• The fourth option is wrong because it describes active transport (which requires energy and moves molecules against the concentration gradient).
• The fifth option is wrong as molecules move from higher to lower concentration in diffusion.

Answer:

It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.