Assertion (A): Retroviruses are modified and used as vectors to deliver desirable genes into animal cells. Reason (R): Retroviruses in animals have the natural ability to transform normal cells into cancerous cells, which provided the knowledge base for generating useful gene delivery tools.
A is True: Disarmed retroviruses are used to deliver genes into animal cells. R is True: Their natural transformation ability provided the basis for developing these vectors. R explains the origin of the tool described in A.
Question 472 of 535
📘 CLASS XII
Assertion (A): The tumor inducing (Ti) plasmid of Agrobacterium tumifaciens is used in its natural, pathogenic form as a cloning vector for gene delivery into dicot plants. Reason (R): Agrobacterium tumifaciens is a pathogen that naturally delivers T-DNA to transform normal plant cells into a tumor.
A is False: The Ti plasmid must be *modified* into a cloning vector, making it non-pathogenic, before use. R is True: Agrobacterium is a dicot pathogen that uses T-DNA to induce tumors.
Question 473 of 535
📘 CLASS XII
Assertion (A): To isolate pure DNA from animal tissue, the cells must be treated with enzymes like cellulase and chitinase. Reason (R): Cell walls and membranes must be broken open to release DNA along with other macromolecules like RNA and proteins.
A is False: Cellulase is used for plant cells and chitinase for fungal cells. R is True: Breaking the cell open is necessary to release the DNA and other macromolecules.
Question 474 of 535
📘 CLASS XII
Assertion (A): Purified DNA ultimately precipitates out of the solution after the addition of chilled ethanol. Reason (R): The precipitated DNA is collected by cutting the DNA bands out of the agarose gel and extracting them through a process called elution.
A is True: DNA precipitates in chilled ethanol as fine threads. R is False: Elution is the process of extracting DNA fragments from the agarose gel piece. The removal of precipitated DNA threads is called spooling.
Question 475 of 535
📘 CLASS XII
Assertion (A): The technique of bioprocess engineering requires the maintenance of a sterile ambience in chemical engineering processes. Reason (R): Maintaining sterility ensures the growth of only the desired microbe or eukaryotic cell in large quantities for manufacturing biotechnological products like antibiotics and vaccines.
A is True: Maintenance of sterile ambience is core to bioprocess engineering. R is True: The goal of maintaining sterility is specifically to allow only the desired organism to grow and produce the product. R explains A.
Question 476 of 535
📘 CLASS XII
Assertion (A): The Polymerase Chain Reaction (PCR) synthesizes multiple copies of the DNA of interest in vitro. Reason (R): The reaction uses two sets of primers, which are small chemically synthesised oligonucleotides complementary to regions of the DNA template.
A is True: PCR is an in vitro amplification technique. R is True: Primers are small, complementary, chemically synthesised oligonucleotides. R describes the tools but does not explain the necessity of the repeating cycles (denaturation/annealing/extension) that makes the high amplification possible (A).
Question 477 of 535
📘 CLASS XII
Assertion (A): A vector should be chosen based on its origin of replication to recover a desired number of copies of the target DNA. Reason (R): The origin of replication sequence is responsible for controlling the copy number of the linked DNA.
A is True: Vector choice depends on the desired copy number. R is True: The ori sequence specifically controls the copy number. R explains the functional basis for the strategic choice mentioned in A.
Question 478 of 535
📘 CLASS XII
Assertion (A): During gel electrophoresis, DNA fragments move towards the cathode (negative electrode) because they are negatively charged molecules. Reason (R): The most commonly used matrix for separation is agarose, a natural polymer extracted from sea weeds, which provides a sieving effect.
A is False: DNA is negatively charged and moves towards the *anode* (positive electrode). R is True: Agarose gel, extracted from sea weeds, is the common matrix that separates DNA fragments by size (sieving effect).
Question 479 of 535
📘 CLASS XII
Assertion (A): Pure DNA fragments in an agarose gel can be seen easily in visible light after staining with ethidium bromide. Reason (R): The separated DNA fragments must be stained with ethidium bromide and exposed to UV radiation, where they appear as bright orange bands.
A is False: Pure DNA fragments cannot be seen in visible light and without UV exposure. R is True: Ethidium bromide staining followed by UV exposure yields bright orange bands.
Question 480 of 535
📘 CLASS XII
Assertion (A): Downstream processing must be applied to all biotechnological products after the biosynthetic stage. Reason (R): This processing is mandatory as it includes separation, purification, formulation with preservatives, and strict quality control testing of the product before marketing.
A is True: Downstream processing is crucial following biosynthesis. R is True: R lists the steps that make DSP mandatory, including quality control, formulation, and purification. R explains A.
