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Board Paper of Class 12-Science 2020 Biology Delhi(Set 2) - Solutions

General Instructions:
Read the following instructions very carefully and strictly follow them:
(i) Question paper comprises five sections – A, B, C, D and E.
(ii) There are 27 questions in the question paper. All questions are compulsory.
(iii) Section A question number 1 to 5 are multiple choice questions, carrying one mark each.
(iv) Section B question number 6 to 12 are short answer questions type-I, carrying two marks each.
(v) Section C question number 13 to 21 are short answer questions type-II, carrying three marks each.
(vi) Section D question number 22 to 24 are short answer questions type-III, carrying three marks each.
(vii) Section E question number 25 to 27 are long answer questions, carrying five marks each.
(viii) Answer should be brief and to the point also the above word limit be adhered to as far as possible.
(ix) There is no overall choice in the question paper. However, an internal choice has been provided in two questions of 1 mark, one question of 2 marks, two questions of 3 marks and three questions of 5 marks questions. Only one of the choices in such questions have to be attempted.
(x) The diagram drawn should be neat proportionate and properly labelled, wherever necessary.
(xi) In addition to this, separate instructions are given with each section and question, wherever necessary.


  • Question 1
    In a bacterium when RNA-polymerase binds to the promoter on a transcription unit during transcription, it
    (a) terminates the process
    (b) helps remove introns
    (c) initiates the process
    (d) inactivates the exons VIEW SOLUTION


  • Question 2
    The first cellular form of life evolved
    (a) in air
    (b) on land
    (c) in water environment
    (d) in deep soil VIEW SOLUTION


  • Question 3
    Mating of a superior male of a breed of a cattle to a superior female of another breed is called
    (a) in breeding
    (b) out crossing
    (c) out breeding
    (d) cross breeding

    OR


    Large-holes in 'Swiss-Cheese' are due to
    (a) Propionibacterium sharmanii
    (b) Saccharomyces cerevisae
    (c) Penicillium chrysogenum
    (d) Acetobacter aceti VIEW SOLUTION


  • Question 4
    Increased concentration of DDT in fish-eating birds is due to
    (a) eutrophication
    (b) bio-magnification
    (c) cultural eutrophication
    (d) accelerated eutrophication

    OR


    Species-Area relationship is represented on a log scale as
    (a) hyperbola
    (b) rectangular hyperbola
    (c) linear
    (d) inverted VIEW SOLUTION


  • Question 5
    Which one of the following part of the plant when put into the soil is likely to produce new offspring?
    (a) Part of an internode
    (b) A stem cutting with a node
    (c) Part of a primary root
    (d) A flower VIEW SOLUTION


  • Question 6
    Name the Scientists and write how did they explain Mendel's laws after the chromosomes were discovered. VIEW SOLUTION


  • Question 7
    State two advantages of an apomictic seed to a farmer. VIEW SOLUTION


  • Question 8
    List two diseases that spread through inhaling droplets or aerosols. Write one prominent symptoms for each one of them. VIEW SOLUTION


  • Question 9
    What makes humus a reservoir of nutrients? Name and write about the process humus undergoes that enriches the soil. VIEW SOLUTION


  • Question 10
    (a) Name the two techniques employed to meet the increasing demand of fish in the world.
    (b) Name any two fresh water fishes.

    OR


    Describe the contributions of Alexander Fleming, Ernest Chain and Howard Florey in the field of microbiology. VIEW SOLUTION


  • Question 11
    All cloning vectors do have a 'selectable marker'. Describe its role in recombinant DNA-technology. VIEW SOLUTION


  • Question 12
    Mention how have plants developed mechanical and chemical defence against herbivores to protect themselves with the help of one example of each. VIEW SOLUTION


  • Question 13
    Explain 'Integrated organic' farming as successfully practiced by Ramesh C. Dagar, a farmer in Sonepat (Haryana). VIEW SOLUTION


  • Question 14
    Explain three different modes of pollination that can occur in chasmogamous flower.

    OR


    Explain the formation of placenta after implantation in a human female. VIEW SOLUTION


  • Question 15
    You are asked to find the genotypes of a tall pea plant growing in your school garden. Name the cross and explain how would you confirm the genotypes. VIEW SOLUTION


  • Question 16
    What are 'SNPs'? Where are they located in a human cell ? State' any two ways the discovery of SNPs can be of importance to humans. VIEW SOLUTION


  • Question 17
    What is adaptive radiation? Explain with the help of a suitable example. VIEW SOLUTION


  • Question 18
    (a) Explain the mode of action of Cu++ releasing IUDs as a good contraceptive. How is hormone releasing IUD different from it?
    (b) Why is “Saheli' a preferred contraceptive by women (any two reasons)? VIEW SOLUTION


  • Question 19
    (a) Explain why bee-hives are setup on the farms for some of our crop-species. Name any two such crop species.
    (b) List any three important steps to be kept in mind for successful bee keeping. VIEW SOLUTION


  • Question 20
    Explain the role of Agrobacterium tumifaciens in developing resistance in tobacco plant against nematode Meloidegyne incognitia. Name the processes responsible for this. VIEW SOLUTION


  • Question 21
    Differentiate between “Pioneer-species”; “Climax-community” and “Seres”.

    OR


    Explain any three ways other than zoological parks, botanical gardens and wildlife safaries, by which threatened species of plants and animals are being conserved 'ex situ'. VIEW SOLUTION


  • Question 22
    Following a road accident four injured persons were brought to a nearby clinic. The doctor immediately injected them with tetanus antitoxin.
    (a) What is tetanus antitoxin ?
    (b) Why were the injured immediately injected with this antitoxin?
    (c) Name the kind of immunity this injection provided. VIEW SOLUTION


  • Question 23
    "The population of a metro city experiences fluctuations in its population density over a period of time.”
    (a) When does the population in a metro city tend to increase?
    (b) When does the population in metro city tend to decline?
    (c) If 'N' is the population density at the time 't', write the population density at the time 't + 1'. VIEW SOLUTION


  • Question 24
    Study the diagram showing the entry of HIV into the human body and be processes that are followed :


    (a) Name the human cell 'A' HIV enters into.
    (b) Mention the genetic material 'B' HIV releases into the cell.
    (c) Identify enzyme 'C'. VIEW SOLUTION


  • Question 25
    (a) Why did T.H. Morgon select Drosophila melanogaster for his experiments?
    (b) How did he disprove Mendelian dihybrid F2 phenotypic ratio of 9 : 3 : 3 : 1? Explain giving reasons.

    OR


    (a) List any four major goals of Human Genome project.
    (b) Write any four ways the knowledge from HGP is of significance for humans.
    (c) Expand BAC and mention its importance. VIEW SOLUTION


  • Question 26
    (a) Name the insect that attacks cotton crops and causes lot of damage to the crop. How has Bt cotton plants overcome this problem and saved the crop ? Explain.
    (b) Write the role of gene Cry IAb.

    OR


    (a) Explain the different steps carried out in Polymerase Chain Reaction, and the specific roles of the enzymes used.

    (b) Mention application of PCR in the field of

    (i) Biotechnology

    (ii) Diagnostics
    VIEW SOLUTION


  • Question 27
    (a) Explain the process of syngamy and triple fusion in angiosperms.
    (b) Trace the development of the product of syngamy upto its mature stage in a dicot plant.
    (c) Draw and label three important parts of a mature dicot embryo.

    OR


    Name the gonadotropins in human. Explain their role in human male and female, respectively. VIEW SOLUTION
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