A carrier protein is required for the transport of these ions across the membrane

Options

A. Polar molecules
B. Non-polar molecules
C. Neutral solutes
D. All of them

Answer

To solve the question about which ions require a carrier protein for transport across the membrane, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carrier Proteins**:
- Carrier proteins are specialized proteins embedded in the cell membrane that facilitate the transport of specific substances across the membrane. They are crucial for the movement of polar and charged molecules that cannot easily pass through the lipid bilayer.

2. **Analyzing the Options**:
- The question provides several options regarding the types of molecules that require carrier proteins for transport.

3. **Evaluating the First Option - Polar Molecules**:
- Polar molecules, due to their hydrophilic nature, cannot easily diffuse through the hydrophobic lipid bilayer of the cell membrane. Therefore, they require carrier proteins to facilitate their transport.
- **Conclusion**: This option is correct.

4. **Evaluating the Second Option - Nonpolar Molecules**:
- Nonpolar molecules are hydrophobic and can easily pass through the lipid bilayer without the need for carrier proteins.
- **Conclusion**: This option is incorrect.

5. **Evaluating the Third Option - Neutral Solutes**:
- Neutral solutes may vary in their ability to cross the membrane. However, many neutral solutes can also diffuse through the membrane without the need for a carrier protein, depending on their size and polarity.
- **Conclusion**: This option is incorrect.

6. **Evaluating the Fourth Option - All of Them**:
- Since only polar molecules require carrier proteins for transport, the statement that all types of molecules require carrier proteins is incorrect.
- **Conclusion**: This option is incorrect.

7. **Final Answer**:
- Based on the evaluations, the correct answer is that **polar molecules** require a carrier protein for transport across the membrane.