The molecule that regularly enters through the inner membrane of mitochondrion is

Options

A. ATP
B. pyruvic acid
C. glucose
D. citric acid

Answer

To solve the question regarding which molecule regularly enters through the inner membrane of the mitochondrion, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context of Cellular Respiration**:
- Cellular respiration is a process that occurs in two main stages: glycolysis and the Krebs cycle (also known as the citric acid cycle).
- Glycolysis occurs in the cytoplasm, where glucose is broken down into pyruvate.

2. **Identify the Role of Pyruvate**:
- After glycolysis, the pyruvate molecules are produced. Each glucose molecule yields two pyruvate molecules.
- These pyruvate molecules need to enter the mitochondria to undergo further processing.

3. **Transport Mechanism**:
- Pyruvate is transported through the inner mitochondrial membrane into the mitochondrial matrix.
- This transport is essential for the pyruvate to enter the Krebs cycle, where it is further oxidized to produce energy.

4. **Evaluate the Options**:
- **ATP**: This is the energy currency of the cell but is produced during cellular respiration, not a molecule that enters the mitochondria.
- **Glucose**: This is the starting molecule for glycolysis and does not enter the mitochondria directly.
- **Citric Acid**: This is a product of the Krebs cycle, not a molecule that enters the mitochondria.
- **Pyruvic Acid**: This is the correct molecule that regularly enters the mitochondria through the inner membrane.

5. **Conclusion**:
- The molecule that regularly enters through the inner membrane of the mitochondrion is **pyruvic acid** (option B).

### Final Answer:
**Pyruvic acid (option B)** is the molecule that regularly enters through the inner membrane of the mitochondrion.

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