Coenobium occurs in

Options

A. Spirogyra
B. Ulothrix
C. Volvox
D. Chlorella.

Answer

**Step-by-Step Solution:**

1. **Understanding Coenobium**: Coenobium refers to a specific arrangement of cells in certain algae where the thallus is non-motile, has a fixed shape, and contains a fixed number of cells. This structure is important for identifying the type of algae.

2. **Analyzing the Options**:
- **Spirogyra**: This is a filamentous green algae that can reproduce both sexually and asexually. It does not form a coenobium structure as it is typically found in long, unbranched filaments.
- **Ulothrix**: This is also a filamentous green algae that is non-branching and can be found in both fresh and saltwater. Like Spirogyra, it does not form a coenobium.
- **Volvox**: This is a colonial green algae that forms hollow spherical or oval colonies. The number of cells in the colony is fixed, ranging from 500 to 60,000 depending on the species. This structure fits the definition of coenobium.
- **Chlorella**: This is a unicellular green algae that exists as single cells without flagella. It does not form a coenobium since it does not have a fixed number of cells in a structured colony.

3. **Conclusion**: Based on the analysis, the only option that fits the definition of coenobium is **Volvox**. Therefore, the correct answer is **Volvox**.

**Final Answer**: Coenobium occurs in **Volvox**.

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