In cells actively participating in protein synthesis and secretion, which of the following organelles is frequently found ?

Options

A. Golgi complex
B. Smooth endoplasmic reticulum
C. Rough endoplasmic reticulum
D. Mitochondria

Answer

To determine which organelle is frequently found in cells actively participating in protein synthesis and secretion, we can analyze the functions of the given organelles step by step.

### Step-by-Step Solution:

1. **Identify the Organelles**: The options provided are likely to include Golgi complex, smooth endoplasmic reticulum (SER), rough endoplasmic reticulum (RER), and mitochondria.

2. **Function of Golgi Complex**: The Golgi complex is primarily involved in the modification, sorting, and packaging of proteins and lipids. It does not directly participate in the synthesis of proteins.

3. **Function of Smooth Endoplasmic Reticulum (SER)**: The SER is involved in lipid synthesis and does not contain ribosomes. Therefore, it is not involved in protein synthesis.

4. **Function of Rough Endoplasmic Reticulum (RER)**: The RER is characterized by the presence of ribosomes on its surface, which are essential for protein synthesis. The ribosomes translate mRNA into polypeptide chains, making the RER a key site for protein synthesis.

5. **Function of Mitochondria**: Mitochondria are known as the powerhouse of the cell, primarily responsible for ATP production through the breakdown of glucose. They do not play a direct role in protein synthesis.

6. **Conclusion**: Based on the functions of these organelles, the rough endoplasmic reticulum (RER) is the organelle that is frequently found in cells actively participating in protein synthesis and secretion due to the presence of ribosomes.

### Answer:
The correct answer is **Rough Endoplasmic Reticulum (RER)**.