Cell theory was given by

Options

A. Robert Hooke
B. Robert Brown
C. Schleiden and Schwann
D. Messelson and Stahl

Answer

**Step-by-Step Solution:**

1. **Identify the Question:**
The question asks about who proposed the cell theory.

2. **Consider the Options:**
The options provided are:
- Robert Hooke
- Robert Brown
- Sheldian and Swan
- Miselson and Stahl

3. **Recall the Contributions of Each Scientist:**
- **Robert Hooke:** He is known for discovering the term "cell" while examining cork under a microscope.
- **Robert Brown:** He discovered the nucleus while studying orchid plants.
- **Sheldian and Swan:** They proposed the cell theory in 1839, which states that:
- Cells are the basic building blocks of all living organisms.
- All living organisms are composed of cells.
- All cells arise from pre-existing cells.
- **Miselson and Stahl:** They conducted an experiment that demonstrated the semi-conservative nature of DNA replication.

4. **Determine the Correct Answer:**
Based on the contributions, the correct answer to the question "Cell theory was given by" is **Sheldian and Swan**.

5. **Conclusion:**
The cell theory is a fundamental concept in biology that outlines the importance of cells in living organisms.