During `N_2` fixation in root nodule to form `NH_3` molecule. How many ATP are consumed ?

Options

A. 16
B. 4
C. 2
D. 8

Answer

To solve the question regarding the number of ATP molecules consumed during nitrogen fixation in root nodules to form ammonia (NH3), we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**: Nitrogen fixation is the process by which nitrogen gas (N2) from the atmosphere is converted into ammonia (NH3). This process occurs in the root nodules of leguminous plants, where symbiotic nitrogen-fixing bacteria (such as Rhizobium) reside.

2. **Role of ATP in Nitrogen Fixation**: During the nitrogen fixation process, energy is required to convert N2 into NH3. This energy is provided in the form of ATP.

3. **Chemical Reaction Involved**: The overall reaction for nitrogen fixation can be summarized as:
\[ N_2 + 8H^+ + 8e^- \rightarrow 2NH_3 + H_2 \]
Here, 8 electrons (e^-) are required to reduce nitrogen gas to ammonia.

4. **ATP Requirement**: According to biochemical studies, it is established that for every mole of nitrogen (N2) fixed, 16 ATP molecules are consumed. However, since each molecule of ammonia (NH3) is produced from this process, we can break it down further:
- For the conversion of 1 mole of N2 to 2 moles of NH3, it is stated that 16 ATP are consumed in total.
- Therefore, for the production of 1 mole of NH3, 8 ATP are consumed.

5. **Final Answer**: Based on the above understanding, the number of ATP molecules consumed during nitrogen fixation to form ammonia is **8 ATP**.

### Conclusion:
The correct answer to the question is **D - 8 ATP**.

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