Question

in what direction do substances diffuse across the cell membrane?
a down the concentration gradient, from an area of lower to higher concentration
b down the concentration gradient, from an area of higher to lower concentration
c against the concentration gradient, from an area of lower to higher concentration
d against the concentration gradient, from an area of higher to lower concentration

Explanation:

Diffusion is the passive movement of substances. It occurs down the concentration gradient, from an area of higher to lower concentration without the use of energy.

Answer:

B. down the concentration gradient, from an area of higher to lower concentration