Number of ATP molecules synthesised through substrate level phosphorylation during aerobic respiration of one glucose molecules is

Options

A. 8
B. 6
C. 4
D. 2

Answer

To determine the number of ATP molecules synthesized through substrate-level phosphorylation during the aerobic respiration of one glucose molecule, we can break down the process into several steps:

### Step-by-Step Solution:

1. **Understanding Substrate-Level Phosphorylation**:
- Substrate-level phosphorylation is a method of forming ATP by directly transferring a phosphate group to ADP from a phosphorylated intermediate.

2. **Identifying the Stages of Aerobic Respiration**:
- Aerobic respiration consists of three main stages: Glycolysis, the Krebs Cycle (Citric Acid Cycle), and the Electron Transport Chain (ETC). However, substrate-level phosphorylation occurs primarily in the first two stages.

3. **Calculating ATP from Glycolysis**:
- During glycolysis, which occurs in the cytoplasm, a total of 4 ATP molecules are produced through substrate-level phosphorylation. However, 2 ATP are consumed in the initial steps, resulting in a net gain of 2 ATP from glycolysis.

4. **Calculating ATP from the Krebs Cycle**:
- In the Krebs Cycle, which occurs in the mitochondria, 2 ATP molecules are synthesized through substrate-level phosphorylation.

5. **Total ATP from Substrate-Level Phosphorylation**:
- Adding the ATP produced from both glycolysis and the Krebs Cycle:
- From Glycolysis: 2 ATP (net gain)
- From Krebs Cycle: 2 ATP
- Total = 2 ATP (from glycolysis) + 2 ATP (from Krebs Cycle) = 4 ATP.

6. **Final Count**:
- Therefore, the total number of ATP molecules synthesized through substrate-level phosphorylation during the aerobic respiration of one glucose molecule is 4 ATP.

### Final Answer:
The number of ATP molecules synthesized through substrate-level phosphorylation during aerobic respiration of one glucose molecule is **4**.