A : Four ATP molecules are produced directly during glycolysis.
R : Substrate level phosphorylation occurs at two steps for a glucose broken down in mitochondrial matrix.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2)
C. If Assertion is true statement but Reason is false, then mark (3)
D. If both Assertion and Reason are false statements, then mark (4)

Answer

To solve the assertion and reason question, we will analyze both the assertion (A) and the reason (R) statements step by step.

### Step 1: Analyze the Assertion (A)
The assertion states: "Four ATP molecules are produced directly during glycolysis."

- Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing ATP and NADH in the process.
- During glycolysis, a total of 4 ATP molecules are produced. However, it is important to note that 2 ATP molecules are consumed in the initial steps of glycolysis.
- Therefore, the net gain of ATP from glycolysis is 2 ATP molecules (4 produced - 2 consumed).
- The assertion is true in terms of gross ATP production.

### Step 2: Analyze the Reason (R)
The reason states: "Substrate level phosphorylation occurs at two steps for a glucose broken down in the mitochondrial matrix."

- Substrate-level phosphorylation refers to the direct synthesis of ATP from ADP and a phosphorylated intermediate.
- In glycolysis, substrate-level phosphorylation occurs at two specific steps:
1. Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate.
2. Conversion of phosphoenolpyruvate (PEP) to pyruvate.
- However, the reason incorrectly states that this process occurs in the mitochondrial matrix. Glycolysis actually occurs in the cytoplasm, not in the mitochondria.
- Therefore, while the concept of substrate-level phosphorylation is correct, the location mentioned is incorrect.

### Conclusion
- The assertion (A) is true: 4 ATP molecules are produced during glycolysis.
- The reason (R) is false: Substrate-level phosphorylation does occur, but not in the mitochondrial matrix.

### Final Answer
The correct answer is that the assertion is true, but the reason is false.

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