Sodium ions are "pumped" from a region of lower concentration to a region of higher concentration in the nerve cells of humans. This process is an example of:
A. osmosis.
B. diffusion.
C. active transport.
D. passive transport.
Diffusion, passive transport and osmosis are examples of movement that does not require cellular energy. Since sodium ions are pumped against the concentration gradient, it requires work and is called active transport.