If a meristematic cell is placed in a medium containing radio active thymidine, radioactivity will be first observed in :-

Options

A. Euchromatin
B. Hetero chromatin
C. Both simultaneously
D. None of these

Answer

To solve the question "If a meristematic cell is placed in a medium containing radioactive thymidine, radioactivity will be first observed in:", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- Meristematic cells are actively dividing cells found in plants. They are responsible for growth and are located in areas such as the tips of roots and shoots.

2. **Identifying the Substance**:
- Radioactive thymidine is a nucleoside that gets incorporated into DNA during the S phase of the cell cycle when DNA is being synthesized.

3. **Examining Chromatin Types**:
- Chromatin exists in two forms: euchromatin and heterochromatin.
- **Euchromatin**: This is the less condensed form of chromatin, which is more accessible for transcription and replication. It allows for easier incorporation of nucleotides, including radioactive thymidine.
- **Heterochromatin**: This is the tightly packed form of chromatin, which is generally transcriptionally inactive and less accessible for the incorporation of nucleotides.

4. **Determining Where Radioactivity Will First Appear**:
- Since radioactive thymidine is incorporated into DNA during replication, and given that euchromatin is less condensed and more accessible, radioactivity will first be observed in euchromatin.

5. **Evaluating the Options**:
- **Option A: Euchromatin** - Correct, as it allows for the incorporation of radioactive thymidine.
- **Option B: Heterochromatin** - Incorrect, as it is tightly packed and less accessible.
- **Option C: Both simultaneously** - Incorrect, as radioactivity will not appear in heterochromatin first.
- **Option D: None of these** - Incorrect, as we have identified euchromatin as the correct answer.

6. **Conclusion**:
- The correct answer is **Euchromatin**.

### Final Answer:
Radioactivity will be first observed in **Euchromatin**.

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