Assertion (A): The Polymerase Chain Reaction (PCR) requires the use of a thermostable DNA polymerase. Reason (R): The thermostable enzyme is required because it remains active and resists inactivation during the high temperature induced denaturation steps of the PCR cycles.
A is True: PCR uses a thermostable DNA polymerase. R is True: The high temperature denaturation steps require an enzyme that remains active, which is why thermostable polymerase is used. R explains A.
Question 452 of 535
📘 CLASS XII
Assertion (A): Bioprocess engineering requires the maintenance of a sterile ambience in chemical engineering processes. Reason (R): Sterility ensures the growth of only the desired microbe or eukaryotic cell in large quantities for the manufacture of biotechnological products.
A is True: Bioprocess engineering involves maintaining a sterile environment (microbial contamination-free). R is True: The purpose of maintaining sterility is specifically to allow only the desired organism to grow and produce the product. R explains A.
Question 453 of 535
📘 CLASS XII
Assertion (A): Small volume cultures cannot yield appreciable quantities of desired protein products. Reason (R): Bioreactors are large vessels (100–1000 litres) used to biologically convert raw materials into specific products using microbial, plant, animal, or human cells.
A is True: Small cultures are insufficient for large-scale production. R is True: Bioreactors were developed to handle large volumes and optimize conditions for high yield. R describes the solution (Bioreactors) to the problem stated in A.
Question 454 of 535
📘 CLASS XII
Assertion (A): DNA fragments are separated in gel electrophoresis based on their size through the sieving effect of the agarose gel. Reason (R): DNA fragments, being negatively charged molecules, move towards the anode (positive electrode) under an electric field.
A is True: DNA fragments resolve (separate) according to size, where smaller fragments move farther. R is True: DNA is negatively charged and moves toward the anode. R describes the *direction* of movement, which is necessary for separation (A), but A describes the *mechanism of separation* (sieving by size). R does not explain A.
Question 455 of 535
📘 CLASS XII
Assertion (A): In gel electrophoresis, separated DNA fragments can only be visualized after staining the gel with ethidium bromide and exposure to UV radiation. Reason (R): Pure DNA fragments are not visible in visible light without staining.
A is True: This is the standard procedure for visualizing DNA bands. R is True: The necessity of the procedure (A) stems directly from the fact that DNA is invisible under visible light without staining. R explains A.
Question 456 of 535
📘 CLASS XII
Assertion (A): The DNA that precipitates out after appropriate treatment and addition of chilled ethanol can be seen as a collection of fine threads in the suspension. Reason (R): This precipitated DNA is removed from the suspension by a process called spooling.
A is True: Purified DNA precipitates in chilled ethanol as fine threads. R is True: The technique used to collect this DNA is called spooling. R describes the subsequent step after A, but does not explain why the DNA appears as fine threads or why it precipitates in ethanol.
Question 457 of 535
📘 CLASS XII
Assertion (A): The techniques of genetic engineering overcome the limitations of traditional hybridisation by allowing scientists to introduce only a specific set of desirable genes. Reason (R): Traditional hybridisation often leads to the inclusion and multiplication of undesirable genes along with the desired ones.
A is True: Genetic engineering allows the introduction of only specific desirable genes. R is True: Traditional methods suffer from introducing undesirable genes. R describes the flaw that genetic engineering (A) was developed to fix, thus R explains A.
Question 458 of 535
📘 CLASS XII
Assertion (A): Micro-injection is the method typically used for introducing recombinant DNA directly into the nucleus of a plant cell. Reason (R): Biolistics (gene gun) method, which uses high velocity micro-particles, is a suitable method for animal cells.
A is False: Micro-injection is used for introducing recombinant DNA into the nucleus of an *animal* cell. R is True: The biolistics method, or gene gun, which bombards cells with micro-particles, is generally suitable for *plants*.
Question 459 of 535
📘 CLASS XII
Assertion (A): For large-scale production, continuous culture systems are used wherein fresh medium is added while used medium is drained out from the other side. Reason (R): Continuous culture maintains the cells in their physiologically most active log/exponential phase, leading to higher yields of the desired protein.
A is True: Continuous culture involves draining used medium and adding fresh medium. R is True: This specific type of culturing method is used because it keeps cells in the log/exponential phase, resulting in larger biomass and higher yields. R explains A.
Question 460 of 535
📘 CLASS XII
Assertion (A): The Ti plasmid of Agrobacterium tumifaciens has been modified into a cloning vector for gene delivery into a variety of plants. Reason (R): Scientists derived knowledge for generating useful vectors by observing how pathogens like Agrobacterium and retroviruses deliver genes to transform eukaryotic cells.
A is True: The tumor inducing (Ti) plasmid has been modified to be non-pathogenic yet capable of delivering genes to plants. R is True: Knowledge about gene delivery by pathogens (like Agrobacterium in plants) provided the basis for developing these vectors. R explains the fundamental knowledge that led to the development described in A.
