In an eukaryotic cell, TCA cycle and electron transport system take place within :

Options

A. nucleolus
B. peroxisomes
C. mitochondria
D. stroma

Explanation

To answer the question, "In an eukaryotic cell, TCA cycle and electron transport system take place within:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the TCA Cycle**:
- The TCA cycle, also known as the tricarboxylic acid cycle, citric acid cycle, or Krebs cycle, is a series of chemical reactions that occur in aerobic organisms to release stored energy. It involves the oxidation of acetyl coenzyme A, which is derived from carbohydrates, fats, or proteins.

2. **Function of the TCA Cycle**:
- The TCA cycle is central to cellular metabolism. It plays a crucial role in energy production and biosynthesis. It completes the breakdown of sugars initiated in glycolysis and contributes to the production of ATP, which is the energy currency of the cell.

3. **Location of the TCA Cycle in Eukaryotic Cells**:
- In eukaryotic cells, the TCA cycle takes place in the mitochondria. This is a key point because the mitochondria are known as the powerhouse of the cell, where energy production occurs.

4. **Understanding the Electron Transport System (ETS)**:
- The electron transport system is a series of proteins that transfer electrons through a membrane within the mitochondria. This process creates a proton gradient that drives the synthesis of ATP.

5. **Function of the Electron Transport System**:
- The ETS is the final step of cellular respiration and is responsible for producing the largest amount of ATP, generating about 34 ATP molecules along with water as a byproduct.

6. **Location of the Electron Transport System in Eukaryotic Cells**:
- Similar to the TCA cycle, the electron transport system also occurs in the mitochondria of eukaryotic cells.

7. **Final Answer**:
- Therefore, in a eukaryotic cell, both the TCA cycle and the electron transport system take place within the mitochondria.

### Final Answer:
**Mitochondria**

---