CBSE Class 12 Biology 2022 — Previous-Year Question Paper

When Plasmodium sp. (malarial parasite) enters the human body, it reproduces asexually and increases its number. During this course, the affected person suffers from malaria. After a number of asexual cycles, the parasite, in order to complete its life cycle, enters the sexual phase of its life. Trace the sexual stages in the life cycle of Plasmodium in a female Anopheles mosquito, when it bites an infected person, up to the formation of mature infective stages of the parasite.

(a) Name and state the type of immunity that acts as a ‘biological shield’ to the developing foetus against many infections in the mother’s womb. (b) A large proportion of infants remain free from potent infections at least three months after birth, or even longer if breast fed. Explain, giving suitable reasons.

With the advent of sophisticated techniques of genetic engineering, we can now readily purify and isolate DNA. Name and explain the different steps involved in the separation and isolation of DNA fragments once cut by restriction endonucleases.

Given below is a picture of a natural large habitat that is being continuously broken into smaller patches. This process is continuing, increasing and expanding over time due to human impact, thereby posing a great risk to the existence of species in the habitat. [Diagram: Original Habitat → Gaps → Gaps created over time due to human activities – “Habitat loss due to creation of ‘patches’ in a habitat”] (a) Do you agree with the above statement ? Give two suitable reasons in support of your answer. (b) Write the ecological term used for such patches formed in an original habitat.

An application of biotechnology in agriculture involves production of pest resistant plants using ‘cry’ genes from a bacterium. Name the bacterium. Explain why the ‘cry’ gene kills the pest but not the bacterium itself.

(a) Development of recombinant DNA technology has opened gates to many breakthroughs in the fields of medicine and agriculture. This has enabled scientists to isolate, sequence and manipulate individual genes obtained from diverse living or dead cells. Given below is a diagram showing the basic steps involved in genetically modifying an organism. Study the given diagram and answer the questions that follow : [Diagram: (1) Restriction Enzyme → (Gene of Interest); (2) Restriction Enzyme → Plasmid (Vector); (X) → (3) rDNA (vector) → (4) E. coli → (5)/(Y)] (i) Are two different types of restriction endonucleases used, one to cut the vector DNA and another to cut the desired DNA to be cloned ? Support your answer, giving reason. (ii) Which enzyme is used at step (X) to integrate the foreign DNA with the vector DNA ? (iii) What is the term used for step (Y) showing multiple copies of the foreign DNA being formed in transformed E. coli ? (iv) Draw a diagram of E. coli cloning vector pBR322 to show the following : (I) Any one restriction endonuclease site in tetracycline resistance gene (II) Any one restriction endonuclease site in ampicillin resistance gene (III) ‘ori’ site (v) What does “rop” code for in plasmid pBR322 ? OR (b) RNA interference (RNAi) holds great potential as a therapeutic agent for the treatment of human diseases and as a bicontrol agent for controlling pests in the agricultural fields. An experiment was conducted to study the use of ‘RNAi’ for the potential treatment of disorders of cholesterol metabolism. Some people possess genetic mutations with elevated levels of ‘ApoB’ gene which predisposes them to coronary artery diseases. Lowering the amount of ‘ApoB’ can reduce the number of lipoproteins and lower the blood cholesterol. Tracy Zimmerman and her colleagues used RNAi in 2006 to reduce the level of ‘ApoB’ in non-human primates Cynomolgus monkeys. (i) One group of monkeys were given RNAi treatment (Small interfering RNAs, SiRNAs) (doses 1 mg/kg SiRNAs), (ii) Second group of monkeys were given RNAi treatment (doses 2·5 mg/kg SiRNAs), and (iii) Third group of monkeys were injected saline as control. The results of the experiments are illustrated in the graph given below : [Graph: Relative serum cholesterol (% per dose) vs Time (hours) 24, 48, 144, 264; bars: Saline X, 1 mg/kg Y, 2·5 mg/kg Z] (i) What do you interpret from the bars (X and Z) obtained after 264 hours of treatment of monkeys with saline and 2·5 mg/kg SiRNAs treatment ? (ii) Name the category of organisms in the living world, where RNA interference (RNAi) takes place. Why ? (iii) What is the basic principle involved in RNA interference (RNAi) in silencing the preferred genes ?