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Board Paper of Class 12 Science Term-II 2022 Biology Delhi(Set 3) - Solutions

General Instructions:

(i) This question paper contains 13 questions. All questions are compulsory.

(ii) The question paper has three sections- Section A, B and C.

(iii) Section-A has 6 questions of 2 marks each. Section-B has 6 questions of 3 marks each; and Section-C has a case-based question of 5 marks.

(iv) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.

(v) Wherever necessary, neat and properly labeled diagrams should be drawn.

  • Question 1
    Many members of genus Glomus form a mycorrhizial association with plants. Elaborate how is this association beneficial to the plants. VIEW SOLUTION

  • Question 2
    State the mode of action of cocaine on human body. Write the scientific name of the source plant it is obtained from.


    Enumerate four most common warning signs of drug and alcohol abuse amongst the youth. VIEW SOLUTION

  • Question 3
    Study the given diagram of Sewage Treatment Plant (S.T.P.) and answer the questions that follow:

    (a) Which one of the two 'S.T.P' (A) or (B) will be more effective in treating the human excreta in the municipal waste?
    (b) Write the steps followed in carrying the treatment of the sewage in step (Z), once the BOD of sewage is reduced significantly till it is passed on to the "anaerobic sludge digesters". VIEW SOLUTION

  • Question 4
    Ringworm is one of the most common infectious fungal disease in humans. Name any two genera of fungi which cause ringworm and state any of its two symptoms. VIEW SOLUTION

  • Question 5
    (i) Write the observations made at the end of Connell's field experiment on barnacles on the rocky sea coasts of Scotland.
    (ii) Name any two categories of organisms that in general are adversely affected by competition.


    The graphs (X) and (Y) given below depict the diurnal variations in the solar radiations in the month of June (Summer) and in December (Winters):

    (i) Which of the two graphs depicts tropical region and temperate regions respectively?
    (ii) Which of the two regions (X) or (Y) will show high biological diversity and why? VIEW SOLUTION

  • Question 6
    What would be the best method to measure the total population density of the number of fishes in river and why? VIEW SOLUTION

  • Question 7
    Many people experience allergic symptoms of sneezing or wheezing on exposure to certain substances in the environment. Give two examples of such substances. Which type of antibodies are produced by the body in response to these substances? Mention the role of mast cells in this kind of allergic response. VIEW SOLUTION

  • Question 8
    (a) Enlist two criteria that are used to identify a region for maximum protection as 'Biodiversity hotspots'

    (b) Name any two "hotspot" regions in our country.


  • Question 9
    'An HIV patient normally doesn't die of 'AIDS', but death is caused due to many other infections.' Do you agree with the statement? Give explanatory reasons in support of your answer. VIEW SOLUTION

  • Question 10
    A cell free method of amplifying DNA first developed in the mid 1980's revolutionized the field of biotechnology. Name the method and explain the basic steps of the technique involved. VIEW SOLUTION

  • Question 11
    Non viral and non vector methods are sometimes used to transfer genes or alien DNA into a plant cell. Explain one such method used in genetic engineering. VIEW SOLUTION

  • Question 12
    (a) How does a gene therapy involving direct modification of the cells, in order to achieve a therapeutic goal is used in the treatment of ADA deficiency? Explain.

    (b) A host cell must be made competent, before it is able to receive an rDNA. Justify.


  • Question 13
    Cloning of genes, play a very Significant role in genetic engineering, helping the transfer of desirable foreign genes into different hosts. The scientists, to make this process easier and effective are creating engineered vectors in such a way that they help easy linking of foreign DNA and selection of recombinants from non recombinants. 'pBR322' is one such engineered vectors developed by scientists. A diagram of an engineered vector pBR322 is given below:

    (i) Name the host for this cloning vector.
    (ii) Identify 'Rop' and 'Ori' in the diagram from 'U', 'V', 'W', 'X', 'Y' and 'Z'. Write their functions.
    (iii) Draw the fragments that will be formed by the action of 'Z' (marked in the diagram) on the specific site of the DNA segment given below:
    5' ---GTACGAATTCCTGA---3'
    3' ---CATGCTTAAGGACT---5'


    RNA interference (RNAi) holds great potential as a therapeutic agent for the treatment of human diseases and as biocontrol agents in controlling pests in the field of agriculture. An experiment was carried 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.
    One group of monkeys were given RNAi treatment (small interfering RNAs, SiRNAs) (doses 1 mg/kg SiRNAs), second group of monkeys were given RNAi treatment (doses 2.5 mg/kg SiRNAs) and third group of monkeys were injected with saline.
    The results of the study are depicted in the graph below:

    (i) How does the treatment with 2.5 mg/kg brings an effect on cholesterol metabolism when compared from 24 hours and 144 hours.
    (ii) Write any two natural sources from where dsRNA molecule could be obtained for silencing the specific mRNA.
    (iii) How is RNAi used in controlling the infection on the roots of tobacco plants by the nematode Meloidogyne incognitia. VIEW SOLUTION
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