In aerobic cellular respiration, most of the ATP is synthesized during :

Options

A. electron transport
B. glycolysis
C. Krebs cycle
D. oxidation of pyruvic acid

Explanation

To answer the question regarding where most of the ATP is synthesized during aerobic cellular respiration, we can follow these steps:

### Step 1: Understand the process of aerobic cellular respiration
Aerobic cellular respiration is a multi-step process that converts glucose into ATP in the presence of oxygen. It consists of three main stages: glycolysis, the Krebs cycle (also known as the citric acid cycle), and the electron transport chain.

### Step 2: Analyze the ATP production in glycolysis
- Glycolysis occurs in the cytoplasm and breaks down one molecule of glucose into two molecules of pyruvate.
- During glycolysis, a net gain of 2 ATP molecules is produced directly.
- Additionally, 2 NADH molecules are generated, which can be converted into ATP during the electron transport chain. Each NADH can yield approximately 2.5 to 3 ATP, leading to a total of about 8 ATP from glycolysis (2 ATP + 2 NADH x 3 ATP/NADH).

### Step 3: Analyze the ATP production in the Krebs cycle
- The Krebs cycle occurs in the mitochondria and processes the pyruvate produced from glycolysis.
- For each glucose molecule, the Krebs cycle turns twice (once for each pyruvate), producing 6 NADH, 2 FADH2, and 2 ATP directly.
- The total ATP yield from the Krebs cycle is significant: 6 NADH can yield approximately 15 ATP (6 x 2.5), 2 FADH2 can yield about 3 ATP (2 x 1.5), and 2 ATP are produced directly, leading to a total of approximately 20 ATP.

### Step 4: Analyze the ATP production in the electron transport chain
- The electron transport chain is where the majority of ATP is generated.
- NADH and FADH2 produced in glycolysis and the Krebs cycle donate electrons to the chain, leading to the production of ATP through oxidative phosphorylation.
- Overall, the complete oxidation of one glucose molecule can yield up to 30-32 ATP when considering all stages.

### Step 5: Conclusion
Based on the analysis, while glycolysis and the Krebs cycle produce ATP, the majority of ATP is synthesized during the electron transport chain. However, if we focus on the Krebs cycle specifically, it is crucial for generating the electron carriers (NADH and FADH2) that ultimately lead to ATP production in the electron transport chain.

### Final Answer
Most of the ATP is synthesized during the **electron transport chain**.

---