Facilitated diffusion differs from ordinary diffusion in that
The Correct Answer and Explanation is:
Correct answer:
Facilitated diffusion differs from ordinary diffusion in that it requires membrane proteins to transport substances across the cell membrane.
Explanation
Facilitated diffusion and ordinary diffusion are both types of passive transport, meaning they do not require energy from the cell to occur. However, the key difference lies in how the substances move across the cell membrane.
Ordinary diffusion, also called simple diffusion, involves the movement of molecules directly through the phospholipid bilayer of the cell membrane. It usually occurs with small, nonpolar molecules such as oxygen, carbon dioxide, and lipid-soluble substances. These molecules move from an area of higher concentration to an area of lower concentration until equilibrium is reached. Since the membrane is semi-permeable, only certain molecules can pass through without assistance.
Facilitated diffusion, on the other hand, is used for molecules that cannot easily pass through the lipid bilayer. This includes large, polar, or charged molecules such as glucose, amino acids, and ions. These molecules require the help of specialized membrane proteins to cross the membrane. These proteins can be either channel proteins, which form pores for specific molecules to pass through, or carrier proteins, which bind to a substance and change shape to shuttle it across the membrane.
Even though facilitated diffusion needs proteins, it is still a passive process because it does not use cellular energy. The movement of substances in facilitated diffusion still follows the concentration gradient — from a region of high concentration to low concentration — but it depends on the availability and function of the specific proteins.
In summary, while both types of diffusion aim to balance concentrations across membranes, facilitated diffusion differs from ordinary diffusion by relying on transport proteins to help larger or charged molecules cross the membrane that cannot diffuse through it directly.
