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Board Paper of Class 12-Science 2008 Biology Delhi(SET 1) - Solutions

General Instructions:
(i) All questions are compulsory.
(ii) This question paper consists of four Sections A, B, C and D. Section A contains 8 questions of one mark each, Section B is of 10 questions of two marks each, Section C is of 9 questions of three marks each and Section D is of 3 questions of five marks each.
(iii) There is no overall choice. However, an internal choice has been provided in one question of 2 marks, one question of 3 marks and two questions of 5 marks weightage. A student has to attempt only one of the alternatives in such questions.
(iv) Wherever necessary, the diagrams drawn should be neat and properly labelled.
  • Question 1

    What causes speciation according to Hugo de Vries?

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  • Question 2

    When and why do some animals such as frogs hibernate?

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  • Question 3

    List any two economically important products for humans obtained from Apis indica.

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  • Question 4

    Name the Indian variety of rice patented by an American company.

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  • Question 5

    What role do macrophages play in providing immunity to humans?

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  • Question 6

    Name the parts ‘A’ and ‘B’ of the transcription unit given below.

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  • Question 7

    Name the world’s most problematic aquatic weed. What is the nature of the water body in which the weeds grow abundantly?

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  • Question 8

    What is the major difference you observe in the offsprings produced by asexual reproduction and in the progeny produced by sexual reproduction?

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  • Question 9

    The flower of brinjal is referred to as chasmogamous while that of beans is cleistogamous. How are they different from each other?

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  • Question 10

    Name the interaction in each of the following:

    (a) Cuckoo lays her eggs in the crow’s nest.

    (b) Orchid grows on a mango tree.

    (c) Ticks live on the skin of dogs.

    (d) Sea anemone is often found on the shell of hermit crab.

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  • Question 11

    A man with blood group A married a woman with B group. They have a son with AB blood group and a daughter with blood group O. Work out the cross and show the possibility of such inheritance.

    OR

    The male fruit fly and female fowl are heterogametic while the female fruit fly and the male fowl are homogametic. Why are they called so?

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  • Question 12

    Why is using tobacco in any form injurious to the health? Explain.

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  • Question 13

    Differentiate between a detritivore and a decomposer giving an example of each.

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  • Question 14

    A mother of one year old daughter wanted to space her second child. Her doctor suggested CuT. Explain its contraceptive actions.

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  • Question 15

    Study the linking of DNA fragments shown above.

    (i) Name ‘a’ DNA and ‘b’ DNA.

    (ii) Name the restriction enzyme that recognises this palindrome.

    (iii) Name the enzyme that can link these two DNA fragments.

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  • Question 16

    What is divergent evolution? Explain taking an example of plants.

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  • Question 17

    Name the blank spaces a, b, c, and d in the table given below:

    Type of Microbe

    Name

    Commercial Product

    Fungus

    a

    Penicillin

    Bacterium

    Acetobacter aceti

    b

    c

    Aspergillus niger

    Citric acid

    Yeast

    d

    Ethanol

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  • Question 18

    Thermal power plants are inevitable in an industrial and densely populated country like ours. What harm do they do to the environment? Also mention any precaution that could be taken to save our environment.

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  • Question 19

    Draw a labelled diagram of the microscopic structure of a human sperm.

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  • Question 20

    Expand MOET. Explain the procedure of this technology in cattle improvement.

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  • Question 21

    One of the codons on mRNA is AUG. Draw the structure of tRNA adapter molecule for this codon. Explain the uniqueness of this tRNA.

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  • Question 22

    Study the population growth curves in the graph given below and answer the questions which follow:

    (i) Identify the growth curves ‘a’ and ‘b’.

    (ii) Which one of them is considered a more realistic one and why?

    (iii) If is the equation of the logistic growth curve, what does K stand for?

    (iv) What is symbolised by N?

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  • Question 23

    How and why is the bacterium Thermus aquaticus employed in recombinant DNA technology? Explain.

    OR

    (a) What are ‘molecular scissors’? Give one example.

    (b) Explain their role in recombinant DNA technology.

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  • Question 24

    Given below is a part of the template strand of a structural gene:

    TAC

    CAT

    TAG

    GAT

    (a) Write its transcribed mRNA strand with its polarity.

    (b) Explain the mechanism involved in initiation of transcription of this strand.

     

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  • Question 25

    (i) How and at what stage does Plasmodium enter into a human body?

    (ii) With the help of a flow-chart only, show the stages of asexual reproduction in the life-cycle of the parasite in the infected human.

    (iii) Why does the victim show symptoms of high fever?

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  • Question 26

    It has been recorded that the temperature of the earth’s atmosphere has increased by 0.6°C.

    (a) What has caused this increase?

    (b) Explain its consequences.

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  • Question 27

    Explain the pattern of inheritance of haemophilia in humans. Why is the possibility of a human female becoming haemophilic extremely rare? Explain.

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  • Question 28

    Draw a labelled diagram of the sectional view of a mature pollen grain in angiosperms. Explain the functions of its different parts.

    OR

    Give a schematic representation of Oogenesis in humans. Mention the number of chromosomes at each stage. Correlate the life phases of the individual with the stages of the process.

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  • Question 29

    (a) Mention the role of vectors in recombinant DNA technology. Give any two examples.

    (b) With the help of diagrammatic representation only, show the steps of recombinant DNA technology.

    OR

    (a) What is plasmid?

    (b) What is meant by ADA deficiency? How is gene therapy a solution to this problem? Why is it not a permanent cure?

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  • Question 30

    Explain Hershey-Chase experiment. What was proved through this experiment?

    OR

    (a) A true breeding pea plant, homozygous for inflated green pods, is crossed with another pea plant with constricted yellow pods (ffgg). What would be the phenotype and genotype of F1 and F2 generations? Give the phenotype ratio of F2 generation.

    (b) State the generalisation proposed by Mendel on the basis of the above mentioned cross.

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