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 of how many ATP molecules are consumed during nitrogen fixation in root nodules to form ammonia (NH₃), we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding Nitrogen Fixation**:
- Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃). This process is crucial for plants as they cannot utilize atmospheric nitrogen directly.

2. **Role of Root Nodules**:
- Root nodules are formed by a symbiotic relationship between leguminous plants and nitrogen-fixing bacteria, such as Rhizobium. These bacteria live in the root nodules and are responsible for the fixation of nitrogen.

3. **Chemical Reaction**:
- The overall reaction for nitrogen fixation can be summarized as:
\[ N_2 + 8H^+ + 8e^- + 16 ATP \rightarrow 2 NH_3 + 16 ADP + 16 P_i \]
- In this reaction, atmospheric nitrogen (N₂) is combined with protons (H⁺) and electrons (e⁻) to form ammonia (NH₃), while consuming ATP.

4. **ATP Consumption**:
- From the reaction, we can see that to produce 2 molecules of ammonia (NH₃), 16 ATP molecules are consumed.
- Therefore, to find out how many ATP are consumed for the formation of a single ammonia molecule, we divide the total ATP consumed by the number of ammonia molecules produced:
\[ \text{ATP per NH}_3 = \frac{16 \text{ ATP}}{2 \text{ NH}_3} = 8 \text{ ATP} \]

5. **Final Answer**:
- Thus, the number of ATP molecules consumed to form one molecule of ammonia (NH₃) during nitrogen fixation is **8 ATP**.