Facilitated diffusion can not cause net transport of molecules from a low to a high concentration. because

Options

A. This would require output of energy
B. This would require input of energy
C. Both (A) and (B)
D. None of these

Answer

### Step-by-Step Solution:

1. **Understanding Facilitated Diffusion**:
- Facilitated diffusion is a process where molecules move across a cell membrane through protein channels. This movement occurs along the concentration gradient, meaning molecules move from an area of higher concentration to an area of lower concentration.

2. **Concentration Gradient**:
- The concentration gradient is the difference in the concentration of a substance between two areas. In facilitated diffusion, molecules naturally flow from a region of high concentration to a region of low concentration, which is a passive process.

3. **Energy Requirement**:
- Facilitated diffusion does not require energy input (ATP) because it relies on the natural tendency of molecules to move down their concentration gradient. If molecules were to move from low to high concentration, it would require energy input to do so, as this is against the natural flow.

4. **Conclusion**:
- Therefore, facilitated diffusion cannot cause net transport of molecules from a low to a high concentration because it does not involve energy expenditure and only allows movement along the concentration gradient.

5. **Final Answer**:
- The correct reasoning is that facilitated diffusion cannot cause net transport from low to high concentration because it requires energy input, which is not utilized in this passive transport mechanism.