The following figure illustrates a plasma membrane. Which substance in the figure is crossing the membrane using simple diffusion?

Question

The following figure illustrates a plasma membrane.  Which substance in the figure is crossing the membrane using simple diffusion?

Quizplus · Accepted Answer

H2O is a small and uncharged molecule that can diffuse through the lipid bilayer of the plasma membrane without the need for a protein channel or carrier. Ca2+, Na+, and K+ are all charged ions that require membrane proteins such as ion channels, ion pumps, or ion exchangers to cross the plasma membrane.

The Following Figure Illustrates a Plasma Membrane