Zoology

To solve the problem, we need to assess the assertion and reason regarding the use of primers in the polymerase chain reaction (PCR) technique.

1. Understanding the Assertion and Reason:
- Assertion (A): Primers are used in the polymerase chain reaction technique.
- Reason (R): Primers are used for the addition of new DNA nucleotides.

2. Analyzing the Assertion (A):
The assertion is correct. In the polymerase chain reaction (PCR), primers are short sequences of nucleotides that provide a starting point for DNA synthesis. They are essential for initiating the process of DNA replication by the DNA polymerase enzyme.

3. Analyzing the Reason (R):
The reason is incorrect. While primers are indeed required in PCR, their role is not to "add new DNA nucleotides." Instead, primers serve as the binding sites for the DNA polymerase to begin DNA synthesis, allowing the enzyme to add nucleotides in the 5' to 3' direction. The actual addition of nucleotides is performed by the DNA polymerase enzyme.

4. Conclusion:
Although the assertion is correct, the reason does not accurately explain why primers are used in PCR. Hence, the correct option is:

Final Answer:
The correct option is (C) A is correct but R is incorrect.

To solve the problem, we need to identify the bacterium commonly used in genetic engineering to produce human insulin chains.

1. Understanding the Process:
In biotechnology, certain bacteria are genetically modified to produce human insulin chains. The most commonly used bacterium for this purpose is Escherichia coli (E. coli), which is known for its ability to take up foreign DNA and produce proteins, such as insulin, from that DNA.

2. Analyzing the Options:
Let's evaluate the provided options:

• S. typhimurium: This bacterium is a pathogen and is not commonly used for insulin production.
• E. coli: This bacterium is widely used in genetic engineering for insulin production. It is a common host for recombinant DNA technology.
• A. tumefaciens: This bacterium is used for plant genetic engineering, not for producing human insulin.
• B. thuringiensis: This bacterium is primarily used as a biopesticide and is not used for insulin production.

3. Conclusion:
The correct bacterium for producing human insulin chains is E. coli.

Final Answer:
The correct answer is (B) E. coli.