Net gain of ATP molecules during aerobic respiration is

Options

A. 36 molecules
B. 38 molecules
C. 40 molecules
D. 48 molecules

Explanation

**Step-by-Step Solution:**

1. **Understanding Aerobic Respiration**: Aerobic respiration is a metabolic process in which glucose is broken down in the presence of oxygen to produce energy in the form of ATP.

2. **Glycolysis**: The first step of aerobic respiration is glycolysis, which occurs in the cytoplasm. During glycolysis, one molecule of glucose is converted into two molecules of pyruvate. This process yields a net gain of 2 ATP molecules.

3. **Pyruvate Oxidation**: The pyruvate produced in glycolysis is then transported into the mitochondria, where it undergoes further processing. Each pyruvate is converted into acetyl-CoA, and during this process, NADH is produced.

4. **Krebs Cycle (Citric Acid Cycle)**: The acetyl-CoA enters the Krebs cycle, which occurs in the mitochondrial matrix. For each turn of the Krebs cycle, 1 ATP is produced directly. Since each glucose molecule produces two acetyl-CoA molecules, the Krebs cycle turns twice for each glucose molecule, resulting in a total of 2 ATP from this cycle.

5. **Electron Transport Chain (ETC)**: The NADH and FADH2 produced in both glycolysis and the Krebs cycle are then used in the electron transport chain, which occurs in the inner mitochondrial membrane. The ETC generates a significant amount of ATP through oxidative phosphorylation. It is estimated that the ETC produces about 34 ATP molecules from the NADH and FADH2 generated.

6. **Total ATP Calculation**: Now, we can sum up the ATP produced from each stage:
- Glycolysis: 2 ATP
- Krebs Cycle: 2 ATP
- Electron Transport Chain: 34 ATP

Therefore, the total net gain of ATP during aerobic respiration is:
\[ 2 \, \text{(from glycolysis)} + 2 \, \text{(from Krebs cycle)} + 34 \, \text{(from ETC)} = 38 \, \text{ATP} \]

7. **Conclusion**: The net gain of ATP molecules during aerobic respiration is 38 ATP.

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