The cell membrane is said to be _____ with respect to the movement of molecules across it

Options

A. Permeable
B. impermeable
C. Semi permeable
D. Selectively permeable

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the nature of the cell membrane concerning the movement of molecules across it. We need to identify the correct term that describes this characteristic.

2. **Evaluating the Options**:
- **Option 1: Permeable**: A permeable membrane allows all fluids and nutrients to pass through. Since the cell membrane does not allow everything to pass freely, this option is incorrect.

- **Option 2: Impermeable**: An impermeable membrane does not allow any fluids or molecules to pass through. This is also incorrect for the cell membrane, as it does allow certain substances to pass.

- **Option 3: Semi-permeable**: A semi-permeable membrane allows the passage of small molecules while restricting larger ones. While this is somewhat accurate, it does not fully describe the selective nature of the cell membrane.

- **Option 4: Selectively Permeable**: This term means that the membrane allows certain molecules to pass while blocking others based on size, charge, or other factors. This accurately describes the cell membrane's function.

3. **Conclusion**: After evaluating all options, the correct answer is that the cell membrane is said to be **selectively permeable** with respect to the movement of molecules across it.

**Final Answer**: The cell membrane is said to be **selectively permeable** with respect to the movement of molecules across it.

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