During aerobic respiration, all the ATPs are synthesized as a result of

Options

A. Oxidative phosphorylation
B. Oxidative and substrate level phosphorylation
C. Substrate level phosphorylation
D. Oxidative and photophosphorylation

Answer

### Step-by-Step Solution:

1. **Understanding Aerobic Respiration**:
- Aerobic respiration is a metabolic process that requires oxygen to produce energy in the form of ATP (adenosine triphosphate). It occurs in the mitochondria of cells.

2. **Identifying ATP Synthesis Mechanisms**:
- There are two main processes through which ATP is synthesized during aerobic respiration: oxidative phosphorylation and substrate-level phosphorylation.

3. **Explaining Oxidative Phosphorylation**:
- Oxidative phosphorylation is the primary method of ATP synthesis in aerobic respiration. It involves the transfer of electrons from NADH (produced during earlier stages of respiration) to oxygen through a series of electron carriers in the electron transport chain (ETC) located in the inner mitochondrial membrane.
- As electrons move through the ETC, protons are pumped into the intermembrane space, creating a proton gradient. The return flow of protons back into the mitochondrial matrix through ATP synthase drives the synthesis of ATP.

4. **Comparing with Substrate-Level Phosphorylation**:
- Substrate-level phosphorylation occurs during glycolysis and the Krebs cycle, where ATP is generated directly from the transfer of a phosphate group to ADP from a phosphorylated intermediate. However, this method is less efficient than oxidative phosphorylation.

5. **Conclusion**:
- Since oxidative phosphorylation is the major source of ATP synthesis during aerobic respiration, the correct answer to the question is "oxidative phosphorylation".

### Final Answer:
During aerobic respiration, all ATPs are synthesized as a result of **oxidative phosphorylation**.

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