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Board Paper of Class 12-Science 2012 Biology (SET 2) - 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

    Cucurbits and papaya plants bear staminate and pistillate flowers. Mention the categories they are put under separately on the basis of the type of flowers they bear. (1)

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  • Question 2

    A garden pea plant (A) produced inflated yellow pod, and another plant (B) of the same species produced constricted green pods. Identify the dominant traits. (1)

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  • Question 3

    Write what do phytophagous insects feed on. (1)

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  • Question 4

    What is the interaction called between Cuscuta and shoe flower bush? (1)

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  • Question 5

    When do the oogenesis and the spermatogenesis initiate in human females and males respectively? (1)

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  • Question 6

    How does smoking tobacco in human lead to oxygen deficiency in their body? (1)

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  • Question 7

    State the significance of the study of fossils in evolution. (1)

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  • Question 8

    Name the following: (1)

    (a) The semi-dwarf variety of wheat is high-yielding and disease-resistant.

    (b) Any one inter-specific hybrid mammal.

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  • Question 9

    (a) Highlight the role of thymus as a lymphoid organ.

    (b) Name the cells that are released from the above mentioned gland. Mention how they help in immunity. (2)

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  • Question 10

    Why do clown fish and sea anemone pair up? What is this relationship called? (2)

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  • Question 11

    Some organisms suspend their metabolic activities to survive in unfavourable conditions. Explain with the help of any four examples. (2)

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  • Question 12

    (a) State the role of DNA ligase in biotechnology.

    (b) What happens when Meloidegyne incognitia consumes cells with RNAi gene? (2)

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  • Question 13

    Draw a schematic diagram of a part of double stranded dinucleotide DNA chain having all the four nitrogenous bases and showing the correct polarity. (2)

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  • Question 14

    Name of parasite the causes filariasis in humans. Mention its two diagnostic symptoms. How is this transmitted to others? (2)

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  • Question 15

    Name the source of streptokinase. How does this bioreactor molecule function in our body? (2)

    OR

    How do mycorrhizae act as biofertilizers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants.

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  • Question 16

    (a) State the difference between meiocyte and gamete with respect to chromosome number.

    (b) Why is a whiptail lizard referred to as parthenogenetic? (2)

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  • Question 17

    Explain the work carried out by Cohen and Boyer that contributed immensely in biotechnology. (2)

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  • Question 18

    Where is sporopollenin present in plants? State its significance with reference to its chemical nature. (2)

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  • Question 19

    Write the function of each of the following: (3)

    (a) Middle piece in human sperm.

    (b) Tapetum in anthers.

    (c) Luteinizing hormone in human males.

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  • Question 20

    Given below is the representation of amino acid composition of the relevant translated portion of β-chain of haemoglobin, related to the shape of human red blood cells. (3)

    (a) Is this representation indicating a normal human or a sufferer from certain related genetic disease? Give reason in support of your answer.

    (b) What difference would be noticed in the phenotype of the normal and the sufferer related to this gene?

    (c) Who are likely to suffer more from the defect related to the gene represented the males, the females or both males and females equally? And why?

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  • Question 21

    Draw a schematic sketch of pBR 322 plasmid and label the following in it: (3)

    (a) Any two restriction sites.

    (b) Ori and rop genes.

    (c) An antibiotic resistant gene.

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  • Question 22

    It is established that RNA is the first genetic material. Explain giving three reasons. (3)

    OR

    (a) Name the enzyme responsible for the transcription of tRNA and the amino acid the initiator tRNA gets linked with.

    (b) Explain the role of initiator tRNA in initiation of protein synthesis.

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  • Question 23

    Study a part of the life cycle of malarial parasite given below. Answer the questions that follow: (3)

    (a) Mention the roles of ‘A’ in the life cycle of the malarial parasite.

    (b) Name the event ‘C’ and the organ where this event occurs.

    (c) Identify the organ ‘B’ and name the cells being released from it.

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  • Question 24

    State the theory of Biogenesis. How does Miller’s experiment support this theory? (3)

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  • Question 25

    Name the genes responsible for making Bt cotton plants resistant to bollworm attack. How do such plants attain resistance against bollworm attacks? Explain. (3)

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  • Question 26

    How does an algal bloom cause eutrophication of a water body? Name the weed that can grow in such a eutrophic lake. (3)

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  • Question 27

    Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. (3)

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  • Question 28

    (a) Draw a ‘pyramid of numbers’ of a situation where a large population of insects feed upon a very big tree. The insects in turn, are eaten by small birds which in turn are fed upon by big birds.

    (b) Differentiate giving reason, between the pyramid of biomass of the above situation and the pyramid of numbers that you have drawn.

    OR

    (a) What are the two types of desirable approaches to conserve biodiversity? Explain with examples bringing out the difference between the two types.

    (b) What is the association between the bumble bee and its favourite orchid Ophrys? How would extinction or change of one affect the other?

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  • Question 29

    What is the inheritance pattern observed in the size of starch grains and seed shape of Pisum sativum? Workout the monohybrid cross showing the above traits. How does this pattern of inheritance deviate from that of Mendelian law of dominance? (5)

    OR

    State the aim and describe Messelson and Stahl’s experiment.

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  • Question 30

    The following is the illustration of the sequence of ovarian events (a − i) in a human female.

    (5)

    (i) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.

    (ii) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.

    (iii) Explain the changes that occur in the uterus simultaneously in anticipation.

    (iv) Write the difference between ‘c’ and ‘h’.

    (v) Draw a labeled sketch of the structure of a human ovum prior to fertilization.

    OR

    How does the megaspore mother cell develop into 7-celled, 8 nucleate embryo sac in an angiosperm? Draw a labeled diagram of a mature embryo sac.

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