Assertion (A): Stirred-tank bioreactors are preferred over small volume cultures for protein production. Reason (R): Small volume cultures cannot yield appreciable quantities of products, while bioreactors handle large volumes (100–1000 litres) and optimize growth conditions.
A is True: Bioreactors are necessary for large scale production. R is True: R explains the inefficiency of small cultures and highlights the large capacity and optimized conditions of bioreactors. R explains A.
Question 482 of 535
📘 CLASS XII
Assertion (A): Micro-injection is the method used for introducing alien DNA into plant cells by bombarding them with high velocity micro-particles. Reason (R): Biolistics, or gene gun, is a method where recombinant DNA is directly injected into the nucleus of an animal cell.
A is False: A describes biolistics/gene gun, which is suitable for plants. Micro-injection is for animal cells. R is False: R confuses the terms; micro-injection is direct injection into the animal nucleus, while biolistics uses micro-particles.
Question 483 of 535
📘 CLASS XII
Assertion (A): The construction of the first recombinant DNA involved linking an antibiotic resistance gene with a native plasmid of Salmonella typhimurium. Reason (R): When this recombinant DNA was transferred into Escherichia coli, it replicated using the new host’s DNA polymerase enzyme and made multiple copies (cloning).
A is True: The first construction linked an antibiotic resistance gene with a plasmid from S. typhimurium. R is True: The transfer to E. coli resulted in replication and cloning of the gene. R describes the successful outcome of the transfer, but not the reason for the initial creation/linking (A).
Question 484 of 535
📘 CLASS XII
Assertion (A): For effective creation of a recombinant DNA molecule, the vector DNA and the source DNA should normally be cut with the same restriction enzyme. Reason (R): Cutting both DNAs with the same restriction enzyme ensures that the resultant fragments have compatible sticky ends, which facilitates the action of DNA ligase.
A is True: Vector and source DNA must generally be cut by the same restriction enzyme. R is True: The purpose is to create matching sticky ends for ligation. R explains A.
Question 485 of 535
📘 CLASS XII
Assertion (A): The procedure for forcing recombinant DNA into competent bacterial cells involves incubating the cells on ice, followed by a brief exposure to $42^circ ext{C}$ (heat shock), and then placing them back on ice. Reason (R): This heat shock procedure is necessary because DNA is a hydrophobic molecule, and this chemical manipulation helps it pass through the cell membranes.
A is True: This describes the physical steps for transformation. R is False: DNA is a *hydrophilic* molecule; its inability to cross the hydrophobic membrane is what necessitates the competency treatment.
Question 486 of 535
📘 CLASS XII
Assertion (A): A DNA palindrome is a sequence of base pairs that reads the same on the two strands when the orientation of reading is kept the same (e.g., $5'\ o 3'$). Reason (R): The word "MALAYALAM" is used as an example because it demonstrates how a word palindrome reads the same when read both forward and backward.
A is True: This is the definition of a DNA palindrome. R is True: MALAYALAM is used as a verbal analogy for a palindrome. R defines an analogy to A, but does not explain the biological significance or function of the DNA sequence (A).
Question 487 of 535
📘 CLASS XII
Assertion (A): Restriction enzymes are generally classified into exonucleases and endonucleases based on where they cut the DNA strand. Reason (R): Endonucleases remove nucleotides from the ends of the DNA, while exonucleases make cuts at specific positions within the DNA.
A is True: Restriction enzymes belong to the nuclease class, which includes exonucleases and endonucleases. R is False: The definitions are reversed. Exonucleases remove nucleotides from the ends; endonucleases cut internally.
Question 488 of 535
📘 CLASS XII
Assertion (A): If any protein encoding gene is expressed in a heterologous host, the resulting protein is called a recombinant protein. Reason (R): Small volume cultures in the laboratory are generally capable of yielding appreciable quantities of the desired recombinant product, making bioreactors unnecessary for scale-up.
A is True: Protein expressed by a cloned gene in a heterologous host is a recombinant protein. R is False: Small volume cultures cannot yield appreciable quantities, necessitating large-scale bioreactors (100–1000 litres).
Question 489 of 535
📘 CLASS XII
Assertion (A): Continuous culture systems are employed for large-scale production in bioreactors. Reason (R): This type of culturing method maintains the cells in their physiologically most active log/exponential phase, leading to higher yields of desired protein.
A is True: Continuous culture is used for multiplication of cells. R is True: The advantage of continuous culture is keeping cells in the log/exponential phase, resulting in higher yields. R explains A.
Question 490 of 535
📘 CLASS XII
Assertion (A): The two core techniques that enabled the birth of modern biotechnology are genetic engineering and bioprocess engineering. Reason (R): Biotechnology products have brought qualitative improvement in health and food production.
A is True: Genetic engineering and bioprocess engineering are the two core techniques. R is True: Biotechnology products have improved health and food production. R states the result/impact, while A lists the foundational techniques. R is not the explanation of A.
