What is correct about the movement of substance across the membrane in facilitated diffusion?

Options

A. it is an active transport
B. it cause transport of molecules from low concentration to high concentration
C. it is insensitive to inhibitors
D. it is a very specific transport

Explanation

### 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 known as carrier proteins.

2. **Identifying Key Characteristics**:
- **Passive Transport**: Facilitated diffusion does not require energy input from the cell. It relies on the concentration gradient, meaning substances move from an area of higher concentration to an area of lower concentration.
- **Specificity**: The process is specific because it involves carrier proteins that only transport certain molecules. Each carrier protein is designed to bind to specific substances.

3. **Analyzing the Options**:
- **Option A: It is an active transport**: This is incorrect. Facilitated diffusion is a passive process, not active transport.
- **Option B: It causes transport of molecules from low concentration to high concentration**: This is also incorrect. Facilitated diffusion moves molecules from high concentration to low concentration.
- **Option C: It is insensitive to inhibitors**: This is incorrect. Facilitated diffusion is sensitive to inhibitors that can block the action of carrier proteins.
- **Option D: It is very specific transport**: This is correct. Facilitated diffusion is indeed very specific due to the involvement of carrier proteins.

4. **Conclusion**: The correct statement about the movement of substances across the membrane in facilitated diffusion is that it is very specific transport.

### Final Answer:
**D: It is very specific transport.**