Most of the oxidative enzymes of the cell and of the Krebs cycle are concentrated within :

Options

A. grana of chloroplasts
B. cristae of mitochondria
C. microsomes
D. ergastoplasm

Explanation

To answer the question, "Most of the oxidative enzymes of the cell and of the Krebs cycle are concentrated within:", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question is asking where the oxidative enzymes, particularly those involved in the Krebs cycle, are primarily located within the cell.

2. **Review the Options**: The options provided are:
- Grana of protoplast
- Cristae of mitochondria
- Microsomes
- Ergistoplasm

3. **Analyze Each Option**:
- **Grana of Protoplast**: Grana are part of chloroplasts involved in photosynthesis, not in the Krebs cycle or oxidative processes. So, this option is incorrect.
- **Cristae of Mitochondria**: The cristae are the inner folds of the mitochondrial membrane where oxidative phosphorylation and the Krebs cycle occur. This option is likely correct.
- **Microsomes**: These are fragments of the endoplasmic reticulum that form when cells are broken down in the lab. They do not play a role in the Krebs cycle. So, this option is incorrect.
- **Ergistoplasm**: This is an alternative name for the endoplasmic reticulum, which is not involved in the Krebs cycle. Therefore, this option is also incorrect.

4. **Conclusion**: Based on the analysis, the correct answer is the **cristae of mitochondria**, as this is where most oxidative enzymes are concentrated and where the Krebs cycle takes place.

### Final Answer:
The correct answer is **cristae of mitochondria**.

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