Differentiate between facilitated and passive diffusion across the membrane with examples.
Passive and Facilitated Diffusion are both energy-independent processes that move molecules across the plasma membrane, but they differ in mechanism and specificity.
Passive Diffusion:
- Small, non-polar molecules such as oxygen ($O_2$) and carbon dioxide ($CO_2$) move directly through the lipid bilayer.
- Molecules move down their concentration gradient without the need for proteins.
- Simple and continuous, but limited by molecule size, polarity, and lipid solubility.
Facilitated Diffusion:
- Polar or larger molecules, like glucose, amino acids, and ions (e.g., $K^+$), require membrane proteins for transport.
- Uses carrier proteins or channel proteins to move molecules down their concentration gradient.
- Examples:
- Glucose enters via GLUT transporters.
- Potassium ions move through specific ion channels.
- More rapid and specific than passive diffusion, but can become saturated when protein carriers are fully occupied.
Both processes are essential for cellular function, ensuring adequate supply of oxygen, nutrients, and ions while maintaining homeostasis according to the cell’s needs and molecular properties.
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