What prevents ions from crossing the plasma membrane via
simple diffusion?
a. ions are too large.
b. ions carry a charge.
c. ions are hydrophobic.
d. ions do not produce a concentration difference.
e. ions cannot interact with membrane-bound
proteins.

Simple diffusion is the concept of a substance moving from an area of high concentration to a lower concentration without energy input. Because the plasma membrane is made of lipids which are non-polar, this membrane readily allows non-polar substances to diffuse through easily. If a substance has a charge like that of an ion, it will be difficult for the ion to cross the plasma membrane through simple diffusion. The answer should be B.