Credit for establishing nucleus as biolgical entity goes to

Options

A. Leeuwenhoek
B. Schwann
C. Koch
D. Robert Brown.

Answer

To solve the question regarding who established the nucleus as a biological entity, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Question**: The question asks who is credited with establishing the nucleus as a biological entity.

2. **Review the Options**: The options provided are:
- A. Livenhoek
- B. Schwan
- C. Koch
- D. Robert Brown

3. **Analyze Each Option**:
- **A. Livenhoek**: Known for discovering living cells in plant tissues, but not specifically for the nucleus.
- **B. Schwan**: Contributed to the cell theory but did not discover the nucleus.
- **C. Koch**: Known for his work on bacteria and diseases, such as tuberculosis and cholera, not for the nucleus.
- **D. Robert Brown**: Credited with the discovery of the nucleus in cells.

4. **Conclude the Answer**: Based on the analysis, Robert Brown is the scientist who first identified the nucleus as a distinct biological entity within the cell.

5. **Final Answer**: The correct answer is **D. Robert Brown**.