Assertion :- On template `5' to 3'` DNA replicate in discontinuous manner.
Reason : DNA polymerase catalyse polymerisation only is one direction that is `5' to 3'.`

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are true but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are false.

Answer

### Step-by-Step Solution:

1. **Understanding the Assertion**: The assertion states that on a template strand that runs from 5' to 3', DNA replicates in a discontinuous manner. This means that the replication does not occur in a continuous flow but rather in segments.

2. **Understanding the Reason**: The reason provided is that DNA polymerase catalyzes polymerization only in one direction, specifically from 5' to 3'. This indicates that the enzyme responsible for DNA synthesis can only add nucleotides to the growing strand in this specific direction.

3. **Analyzing the Template Strand**: In DNA replication, there are two strands: the leading strand and the lagging strand. The leading strand is synthesized continuously in the 5' to 3' direction, while the lagging strand is synthesized discontinuously, forming short segments known as Okazaki fragments.

4. **Linking Assertion and Reason**: Since DNA polymerase can only synthesize DNA in the 5' to 3' direction, when it encounters a template strand that runs in the opposite direction (3' to 5'), it cannot synthesize continuously. This results in the formation of Okazaki fragments, thereby supporting the assertion that replication occurs in a discontinuous manner on a 5' to 3' template strand.

5. **Conclusion**: Both the assertion and the reason are true, and the reason correctly explains the assertion. Therefore, the correct answer is that both the assertion and reason are true, and the reason is the correct explanation of the assertion.

### Final Answer:
**Option A**: Both assertion and reason are true, and the reason is the correct explanation of the assertion.

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