Carrier proteins for active salt uptake

Options

A. have pores
B. from complex with ions
C. function uner transpiration pull
D. All of the above

Answer

### Step-by-Step Solution:

1. **Understanding Carrier Proteins**:
- Carrier proteins are integral membrane proteins that facilitate the transport of substances across the cell membrane. They are crucial for the active uptake of ions and other solutes.

2. **Role of Carrier Proteins in Active Transport**:
- Active transport is the process where substances are moved against their concentration gradient, which requires energy, usually in the form of ATP. Carrier proteins are essential for this process.

3. **Mechanism of Action**:
- When a salt ion (such as Na+ or K+) approaches a carrier protein, it binds to the protein, forming a complex. This binding induces a conformational change in the carrier protein.

4. **Transport Process**:
- After the conformational change, the carrier protein reorients itself, effectively transporting the ion across the membrane and releasing it into the cytoplasm of the cell.

5. **Comparison with Other Mechanisms**:
- Unlike channels or pores that allow passive transport of substances (like water), carrier proteins specifically bind to ions and facilitate their movement through active transport.
- The transpiration pull is related to water movement in plants and does not involve carrier proteins directly.

6. **Conclusion**:
- Therefore, the correct function of carrier proteins in the context of active salt uptake is that they "form complexes with the ions."

### Final Answer:
The correct option is that carrier proteins for active salt uptake "form complexes with the ions."

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