During which stage in the complete oxidation of glucose are the greatest number of ATP molecules formed from ADP
Or
Largest amount of phosphate bond energy is produced in the process of respiration during

Options

A. (a) Electron transport chain
B. (b) Glycolysis
C. (c) Krebs' cycle
D. (d) Oxidation of pyruvic acid

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks during which stage of the complete oxidation of glucose the greatest number of ATP molecules are formed from ADP, or where the largest amount of phosphate bond energy is produced.

2. **Stages of Respiration**: The complete oxidation of glucose involves several stages:
- Glycolysis
- Conversion of pyruvate to acetyl-CoA
- Krebs Cycle (Citric Acid Cycle)
- Electron Transport Chain (ETC)

3. **ATP Production in Glycolysis**:
- Glycolysis converts glucose to pyruvate and produces a net yield of 2 ATP molecules directly.
- Additionally, it produces 2 NADH, which can generate more ATP in the ETC.

4. **ATP Production from Pyruvate to Acetyl-CoA**:
- The conversion of pyruvate to acetyl-CoA produces 2 NADH, which can yield approximately 5 ATP when processed in the ETC.

5. **ATP Production in the Krebs Cycle**:
- The Krebs Cycle produces 2 ATP directly.
- It also generates 6 NADH and 2 FADH2, which can yield about 15 ATP and 3 ATP respectively when processed in the ETC.

6. **Total ATP Calculation**:
- Glycolysis: 2 ATP + 5 ATP (from NADH) = 7 ATP
- Pyruvate to Acetyl-CoA: 5 ATP (from NADH)
- Krebs Cycle: 2 ATP + 15 ATP (from NADH) + 3 ATP (from FADH2) = 20 ATP
- Total ATP from all stages = 7 ATP + 5 ATP + 20 ATP = 32 ATP

7. **ATP Production in the Electron Transport Chain (ETC)**:
- The ETC is where the majority of ATP is produced through oxidative phosphorylation. It utilizes the NADH and FADH2 generated in previous stages to produce approximately 34 ATP.

8. **Conclusion**: The stage where the greatest number of ATP molecules are formed from ADP is during the Electron Transport Chain (ETC).

**Final Answer**: The greatest number of ATP molecules are formed during the Electron Transport Chain (ETC).

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