Select an incorrect statement for facilitated diffusion

Options

A. Substances soluble in lipids diffuse through the membrane faster.
B. Creates concentration gradient
C. Special proteins help in movement substances across membranes without expenditure of ATP energy
D. Transport rate reaches a maximum when all of the protein transporters are being used

Answer

To determine the incorrect statement regarding facilitated diffusion, we will analyze the characteristics of facilitated diffusion step by step.

### Step-by-Step Solution:

1. **Understanding Facilitated Diffusion**:
- Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special proteins.

2. **Direction of Transport**:
- In facilitated diffusion, substances move along the concentration gradient, meaning they move from an area of higher concentration to an area of lower concentration.

3. **Energy Requirement**:
- Since facilitated diffusion is a passive process, it does not require ATP (adenosine triphosphate) for energy.

4. **Role of Membrane Proteins**:
- Specific membrane proteins (transporters or carriers) are necessary for the transport of substances during facilitated diffusion.

5. **Factors Affecting Rate of Diffusion**:
- The rate of diffusion can depend on several factors:
- **Size of the Substance**: Smaller substances tend to diffuse faster.
- **Solubility in Lipids**: Substances that are more soluble in lipids will diffuse more quickly across the membrane.
- **Nature of the Substance**: Hydrophilic substances may have difficulty crossing the lipid bilayer without assistance.

6. **Concentration Gradient**:
- An important point is that facilitated diffusion does not create a concentration gradient; it utilizes an existing gradient. Therefore, if a statement claims that facilitated diffusion creates a concentration gradient, it is incorrect.

7. **Saturation Kinetics**:
- When all available transport proteins are occupied, the rate of transport reaches a maximum, which is known as saturation kinetics.

### Conclusion:
The incorrect statement regarding facilitated diffusion is that it "creates a concentration gradient." Instead, facilitated diffusion relies on an existing concentration gradient.