Facilitated diffusion differs from ordinary diffusion in that facilitated diffusion.
The Correct Answer and Explanation is :
Correct Answer: Facilitated diffusion differs from ordinary diffusion in that it requires specific membrane proteins to assist in the transport of substances across the cell membrane.
Explanation:
Facilitated diffusion is a type of passive transport that enables molecules to move across a cell membrane with the help of specialized membrane proteins, such as carrier proteins or channel proteins. It is distinct from ordinary diffusion in several key ways, though both processes rely on the principle of moving substances down their concentration gradient (from areas of higher concentration to areas of lower concentration).
- Requirement for Proteins:
Ordinary diffusion does not involve any assistance from proteins; molecules pass directly through the phospholipid bilayer of the membrane. This is typically limited to small, nonpolar molecules like oxygen, carbon dioxide, and lipid-soluble substances. Facilitated diffusion, on the other hand, is necessary for molecules that are too large, polar, or charged (e.g., glucose, amino acids, or ions) to diffuse directly through the hydrophobic core of the lipid bilayer. - Selectivity:
Facilitated diffusion is highly selective due to the involvement of specific proteins. For instance, glucose transporters allow only glucose molecules to pass, while ion channels may be selective for particular ions like sodium or potassium. - Efficiency for Certain Molecules:
In facilitated diffusion, the transport rate is often faster for specific substances because the proteins provide a pathway that bypasses the membrane’s resistance to polar or charged molecules. - Saturation Kinetics:
Unlike ordinary diffusion, the rate of facilitated diffusion can reach a maximum when all the available transport proteins are occupied, a phenomenon known as saturation. This is not observed in ordinary diffusion, which depends purely on the concentration gradient.
Despite these differences, both processes are energy-independent and rely solely on the concentration gradient, making them distinct from active transport, which requires energy input (ATP). Facilitated diffusion is essential for maintaining cellular homeostasis and transporting critical substances efficiently in biological systems.