Some protists possess structures for regulation of their water content. They are

Options

A. Nuclei
B. Contractile vacuoles
C. Chromatophores
D. Membranes.

Answer

To solve the question regarding which structures in protists help in the regulation of their water content, we can analyze the provided options step by step.

**Step 1: Understand the Options**
The question provides four options:
1. Nuclei
2. Contractile vacuoles
3. Chromatophores
4. Membranes

**Step 2: Analyze Each Option**
- **Nuclei**: The nucleus is primarily responsible for housing genetic material and does not play a role in water regulation. Therefore, this option is incorrect.

- **Contractile Vacuoles**: These structures are found in freshwater protists. Their main function is to expel excess water from the cell, thus helping in osmoregulation and preventing the cell from bursting due to excess water intake. This option is correct.

- **Chromatophores**: These are pigment-containing organelles found in some protists that are involved in photosynthesis and do not regulate water content. Hence, this option is incorrect.

- **Membranes**: While membranes provide protection and structure to the cell, they do not specifically regulate water content. Thus, this option is also incorrect.

**Step 3: Conclusion**
After analyzing all options, the only structure that helps in the regulation of water content in protists is the **contractile vacuoles**.

**Final Answer**: The structures for regulation of water content in some protists are **contractile vacuoles**.

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