Which is correct?

Options

A. Legumes fix nitrogen through bacteria in their leaves
B. Legumes fix nitrogens through bacteria in their roots
C. Legumes fix nitrogens independent of bacteria
D. Legumes do not fix nitrogen.

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which statement is correct regarding how legumes fix nitrogen. The two options presented are:
- Legumes fix nitrogen through bacteria in their leaves.
- Legumes fix nitrogen through bacteria in their roots.

2. **Analyzing the First Statement**: The first statement claims that legumes fix nitrogen through bacteria in their leaves. This is incorrect. While leaves may play a role in photosynthesis and gas exchange, nitrogen fixation in legumes does not occur in the leaves.

3. **Analyzing the Second Statement**: The second statement claims that legumes fix nitrogen through bacteria in their roots. This is correct. Legumes form symbiotic relationships with nitrogen-fixing bacteria, primarily Rhizobium, which reside in root nodules.

4. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process of converting atmospheric nitrogen (N2) into ammonia (NH3). This process is crucial for making nitrogen available to plants, as they cannot utilize atmospheric nitrogen directly.

5. **Role of Leg Hemoglobin**: In the root nodules of legumes, there is a protein called leghemoglobin. This protein helps maintain an anaerobic environment necessary for the nitrogen-fixing bacteria to function effectively. It binds oxygen, ensuring that the bacteria can convert nitrogen to ammonia without interference from oxygen.

6. **Conclusion**: Based on the analysis, the correct statement is that legumes fix nitrogen through bacteria in their roots.

### Final Answer:
The correct statement is: "Legumes fix nitrogen through bacteria in their roots."

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