Which of the following statements is correct about diffusion?
a) it may require a transport protein.
b) it is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.
c) it requires an expenditure of energy by the cell.
d) it involves movement of molecules down a concentration gradient and may require a transport protein.
e) it is an active process in which molecules move from a region of lower concentration to one of higher concentration.

The right answer is B.

Diffusion is a passive transport (without energy, nor transport proteins) spreading a substance, a wave, in all directions by following the concentration gradient (from most concentrated to at least concentrated).

A number of small molecules O2, CO2, fatty acids, ethanol, can freely cross the cytoplasmic membrane when their concentration in the extracellular medium is greater than that of the intracellular medium.

The correct answer is option B) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.

Explanation:

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Diffusion is a passive transport process. It does not require transport proteins.

This transport happens from a region of greater concentration, to that of less concentration.

This is called concentration gradient.

After the analysis we conclude, that the correct answer is option B) It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration.