Differentiate between Simple and Facilitated Diffusion
Simple and facilitated diffusion are both passive transport mechanisms by which molecules move across biological membranes. However, they differ in the mechanisms and types of molecules involved.
Simple Diffusion
- Occurs directly through the lipid bilayer without the involvement of membrane proteins.
- Primarily allows the passage of small, non-polar molecules such as oxygen (O₂), carbon dioxide (CO₂), and lipophilic substances.
- Driven solely by the concentration gradient (from high to low concentration).
- No energy or protein assistance is required.
- Occurs continuously until equilibrium is reached.
Facilitated Diffusion
- Involves specific membrane proteins such as carrier proteins or channel proteins.
- Transports polar or charged molecules (e.g., glucose, amino acids, ions) that cannot freely cross the hydrophobic core of the membrane.
- Also occurs down the concentration gradient, so it is a passive process (no energy input).
- Can be selective, saturable, and sometimes regulated by cellular signals.
Summary
While both are passive, simple diffusion allows unrestricted movement of small molecules through the lipid bilayer, whereas facilitated diffusion requires membrane proteins to transport specific molecules. Facilitated diffusion increases the efficiency and specificity of transport, critical for maintaining cellular homeostasis.