Heterocysts are present in `BGA` which participate in __________and lack ____________.

Options

A. `N_(2)-"fix",PS-II`
B. `N_(2)-"fix",PS-I`
C. denitrification, `PS-II`
D. dentrification, `PS-I`

Answer

**Step-by-Step Solution:**

1. **Understanding Heterocysts**: Heterocysts are specialized cells found in certain filamentous cyanobacteria (blue-green algae, BGA) such as Nostoc and Anabaena. They are formed in response to nitrogen starvation.

2. **Function of Heterocysts**: The primary function of heterocysts is to fix atmospheric nitrogen (N2) into ammonia (NH3) or other nitrogenous compounds. This process is crucial for the nitrogen cycle and helps in providing nitrogen to the ecosystem.

3. **Identifying the Process**: Since heterocysts are involved in the fixation of nitrogen, we can conclude that they participate in nitrogen fixation.

4. **Understanding the Lack of Photosystems**: Heterocysts lack Photosystem II (PS2). This is important because PS2 is involved in the splitting of water during photosynthesis, a process that does not occur in heterocysts. Instead, heterocysts rely on anaerobic conditions to fix nitrogen.

5. **Final Answer**: Therefore, the complete statement is: "Heterocysts are present in BGA which participate in nitrogen fixation and lack Photosystem II."

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