Nostoc is known to do

Options

A. photosynthesis
B. photosynthesis and `N_2` fixation simul taneously
C. `N_2` fixation only
D. either photosynthesis or `N_2` fixation at a time

Answer

To answer the question "Nostoc is known to do," we will analyze the options provided and the characteristics of Nostoc.

### Step-by-Step Solution:

1. **Identify Nostoc**: Nostoc is a genus of cyanobacteria, which are photosynthetic microorganisms. They are often found in water bodies and moist soils.

2. **Understand the Functions of Nostoc**:
- Nostoc is known for two main functions:
- **Photosynthesis**: This process involves the conversion of light energy into chemical energy, using chlorophyll pigments.
- **Nitrogen Fixation**: This is the process of converting atmospheric nitrogen (N2) into ammonia (NH3), which can be utilized by plants.

3. **Evaluate the Options**:
- **Option 1**: Photosynthesis - This option is incomplete because it does not mention nitrogen fixation.
- **Option 2**: Photosynthesis and nitrogen fixation simultaneously - This option accurately describes the capabilities of Nostoc.
- **Option 3**: Nitrogen fixation only - This option is incorrect as it ignores the photosynthetic ability of Nostoc.
- **Option 4**: Either photosynthesis or nitrogen fixation at a time - This option is also incorrect because Nostoc can perform both processes simultaneously.

4. **Conclusion**: Based on the analysis, the correct answer is **Option 2: Photosynthesis and nitrogen fixation simultaneously**.

### Final Answer:
Nostoc is known to do photosynthesis and nitrogen fixation simultaneously.

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