Osmoregulation is maintained by

Options

A. Plasma membrane
B. Nuclear membrane
C. Tonoplast
D. 1 & 3

Answer

### Step-by-Step Text Solution:

1. **Understanding Osmoregulation**:
- Osmoregulation refers to the process by which cells and organisms maintain the balance of water and solutes (like salts) in their bodies. This is crucial for cellular function and overall homeostasis.

2. **Defining Key Terms**:
- The term "osmotic potential" relates to the tendency of water to move across a semi-permeable membrane due to differences in solute concentration. Osmoregulation is essentially about managing this osmotic potential.

3. **Role of Membranes in Osmoregulation**:
- The plasma membrane, which surrounds the cell, is a semi-permeable membrane. This means it allows certain substances to pass while blocking others. This characteristic is essential for osmosis, the process by which water moves across the membrane to balance solute concentrations inside and outside the cell.

4. **Identifying the Correct Structures**:
- Among the options given (plasma membrane, nuclear membrane, tonoplast), the plasma membrane is the primary structure responsible for osmoregulation due to its semi-permeable nature.
- The nuclear membrane primarily protects the nucleus and does not play a direct role in osmoregulation.
- The tonoplast is the membrane surrounding the vacuole in plant cells and can also contribute to osmoregulation by managing water storage and solute concentration within the vacuole.

5. **Conclusion**:
- Therefore, both the plasma membrane and the tonoplast are involved in osmoregulation, making options 1 (plasma membrane) and 3 (tonoplast) correct.

### Final Answer:
Osmoregulation is maintained by the plasma membrane and the tonoplast (options 1 and 3).

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