How much of the energy released during aerobic respiration is approximately conserved in the form of ATP

Options

A. 0.2
B. 0.4
C. 0.6
D. 1

Answer

### Step-by-Step Solution:

1. **Understanding Aerobic Respiration**:
- Aerobic respiration is a process that converts glucose and oxygen into carbon dioxide, water, and energy in the form of ATP.

2. **Glycolysis**:
- Glycolysis occurs in the cytoplasm and involves two phases: the preparatory phase and the payoff phase.
- In the preparatory phase, 2 ATP are consumed.
- In the payoff phase, 4 ATP are produced.
- Therefore, the net gain from glycolysis is:
\[ \text{Net ATP from Glycolysis} = 4 \text{ ATP produced} - 2 \text{ ATP used} = 2 \text{ ATP} \]
- Additionally, 2 NADH molecules are produced during glycolysis.

3. **Calculating ATP from NADH**:
- Each NADH can be converted into approximately 3 ATP during oxidative phosphorylation.
- Thus, the ATP yield from NADH is:
\[ 2 \text{ NADH} \times 3 \text{ ATP/NADH} = 6 \text{ ATP} \]

4. **Total ATP from Glycolysis**:
- Adding the net ATP from glycolysis and the ATP from NADH:
\[ \text{Total ATP from Glycolysis} = 2 \text{ ATP} + 6 \text{ ATP} = 8 \text{ ATP} \]

5. **Conversion of Pyruvate to Acetyl CoA**:
- Each glucose molecule produces 2 pyruvate molecules, and each conversion of pyruvate to acetyl CoA produces 2 NADH.
- Therefore, from 2 pyruvate, we get:
\[ 2 \text{ NADH} \times 3 \text{ ATP/NADH} = 6 \text{ ATP} \]

6. **Krebs Cycle**:
- Each acetyl CoA enters the Krebs cycle. Since there are 2 acetyl CoA from 1 glucose, we consider 2 cycles.
- In one cycle, the ATP yield is:
- 3 NADH (producing 9 ATP)
- 1 FADH (producing 2 ATP)
- 1 GTP (equivalent to 1 ATP)
- Therefore, for 2 cycles:
\[ \text{Total from Krebs Cycle} = 2 \times (3 \text{ NADH} \times 3 + 1 \text{ FADH} \times 2 + 1 \text{ GTP}) = 2 \times (9 + 2 + 2) = 2 \times 13 = 26 \text{ ATP} \]

7. **Total ATP from Aerobic Respiration**:
- Adding all ATP yields together:
\[ \text{Total ATP} = \text{ATP from Glycolysis} + \text{ATP from Pyruvate Conversion} + \text{ATP from Krebs Cycle} \]
\[ = 8 \text{ ATP} + 6 \text{ ATP} + 26 \text{ ATP} = 38 \text{ ATP} \]

8. **Energy Conservation Calculation**:
- The free energy released during the oxidation of glucose is approximately -686 kcal/mol.
- Each ATP molecule releases about 7.3 kcal when hydrolyzed.
- Therefore, the total energy conserved in the form of ATP is:
\[ \text{Energy conserved} = 38 \text{ ATP} \times 7.3 \text{ kcal/ATP} = 277.4 \text{ kcal} \]
- To find the fraction of energy conserved:
\[ \text{Fraction of energy conserved} = \frac{277.4 \text{ kcal}}{686 \text{ kcal}} \approx 0.404 \]
- Thus, approximately 0.4 of the energy released during aerobic respiration is conserved in the form of ATP.

### Final Answer:
Approximately 0.4 of the energy released during aerobic respiration is conserved in the form of ATP.

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