The main difference between active and passive transport across cell membrane is that

Options

A. Active transport is more rapid than passive
B. Passive tranport is non selective
C. Passive transport is due to the concentration gradient across the cell membrane whereas active transport is due to metabolic energy
D. Passive transport is confined to anions whereas active transport is confined to cations only

Answer

**Step-by-Step Text Solution:**

1. **Definition of Active and Passive Transport**:
- Active transport is the movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration, which requires energy (ATP).
- Passive transport is the movement of molecules from a region of higher concentration to a region of lower concentration, which does not require energy.

2. **Energy Requirement**:
- Active transport requires metabolic energy (ATP) to move substances against their concentration gradient.
- Passive transport does not require energy, as it relies on the natural kinetic energy of molecules and the concentration gradient.

3. **Direction of Movement**:
- In active transport, substances move against the concentration gradient (from low to high concentration).
- In passive transport, substances move along the concentration gradient (from high to low concentration).

4. **Examples**:
- Examples of passive transport include simple diffusion and facilitated diffusion. Both processes allow molecules to move without the use of energy.
- An example of active transport is the sodium-potassium pump, which moves sodium ions out of the cell and potassium ions into the cell against their respective concentration gradients.

5. **Selectivity**:
- Passive transport can be selective, especially in facilitated diffusion, where specific proteins help transport certain molecules.
- Active transport is also selective, as it often involves specific transport proteins that move particular ions or molecules.

6. **Conclusion**:
- The main difference between active and passive transport is that active transport requires energy to move substances against their concentration gradient, while passive transport occurs naturally along the concentration gradient without energy input.

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