Which of the following factors does not affect the rate of simple diffusion ?

Options

A. The permeability of the membrane
B. The number of transport proteins in the membrane
C. The gradient of concentration
D. Temperature and pressure

Answer

To determine which factor does not affect the rate of simple diffusion, we need to analyze the options provided based on the principles of diffusion.

### Step-by-Step Solution:

1. **Understanding Simple Diffusion**: Simple diffusion is the passive movement of substances from an area of higher concentration to an area of lower concentration. It does not require energy and is influenced by various factors.

2. **Factors Affecting Simple Diffusion**:
- **Membrane Permeability**: The permeability of the membrane is crucial because it determines how easily substances can pass through. A more permeable membrane allows for a higher rate of diffusion.
- **Concentration Gradient**: The difference in concentration between two areas (the concentration gradient) directly affects the rate of diffusion. A steeper gradient results in a faster diffusion rate.
- **Temperature and Pressure**: Higher temperatures generally increase the kinetic energy of molecules, leading to a faster rate of diffusion. Similarly, changes in pressure can influence the movement of molecules.

3. **Analyzing the Options**:
- **Option A (Membrane Permeability)**: This does affect the rate of diffusion.
- **Option B (Number of Transport Proteins)**: This is the correct answer because the number of transport proteins is related to facilitated diffusion, not simple diffusion. Simple diffusion does not involve transport proteins.
- **Option C (Concentration Gradient)**: This does affect the rate of diffusion.
- **Option D (Temperature and Pressure)**: This also affects the rate of diffusion.

4. **Conclusion**: The factor that does not affect the rate of simple diffusion is the **number of transport proteins in the membrane**.

### Final Answer:
**The number of transport proteins in the membrane does not affect the rate of simple diffusion.**