For diffusion to occur, which condition must be met?

A) A concentration gradient must exist.

B) A hypotonic external environment is required.

C) A hypertonic external environment is required.

D) Dynamic equilibrium must exist.

For diffusion to occur, the condition that must be met is that a concentration gradient must exist. The answer is letter A. The movement is always from a higher concentration to a lower concentration. The rest of the choices do not answer the question above.