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Board Paper of Class 12-Science 2010 Biology Delhi(SET 3) - 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

    Mention one positive and one negative application of amniocentesis.

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  • Question 2

    How do animals like fish and snails avoid summer related unfavourable conditions?

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  • Question 3

    In a pond there were 200 frogs. 40 more were born in a year. Calculate the birth rate of the population.

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  • Question 4

    Mention two functions of the codon AUG.

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  • Question 5

    Name a molecular diagnostic technique to detect the presence of a pathogen in its early stage of infection.

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  • Question 6

    Name the scientist who disproved spontaneous generation theory.

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  • Question 7

    What is it that prevents a child to suffer from a disease he/she is vaccinated against? Give one reason.

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  • Question 8

    Why is the enzyme cellulose used for isolating genetic material from plant cells but not for animal cells?

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  • Question 9

    Where does triple fusion take place in a flowering plant? Why is it so called? Mention its significance.

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  • Question 10

    Why certain regions have declared as biodiversity “hot spots” by environmentalists of the world? Name any two “hot spot” regions of India.

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  • Question 11

    A moss plant produces a large number of antherozoids but relatively only a few egg cells. Why?

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  • Question 12

    Why is the introduction of genetically engineered lymphocytes into a ADA deficiency patient not a permanent cure? Suggest a possible permanent cure.

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  • Question 13

    Study the given food chain and answer the questions that follow:

    (i) Give reasons why there is a continuous increase in the DDT content in different trophic levels of the chain.

    (ii) Name the phenomenon responsible for the increase in DDT content.

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  • Question 14

    Honey collection improves when beehives are kept in crop-fields during flowering season. Explain.

    OR

    How does addition of a small amount of curd to fresh milk help formation of curd? Mention a nutritional quality that gets added to the curd.

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  • Question 15

    Name the type of food chains responsible for the flow of larger fraction of energy in an aquatic and a terrestrial ecosystem respectively. Mention one difference between the two food chains.

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  • Question 16

    Name the host and the site where the following occur in the life-cycle of a malarial parasite:

    (a) Formation of gametocytes

    (b) Fusion of gametocytes

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  • Question 17

    Why are F2 phenotypic and genotypic ratios same in a cross between red-flowered snapdragon and white-flowered snapdragon plants. Explain with the help of a cross.

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  • Question 18

    How does the floral pattern of Mediterranean orchid Ophrys guarantee cross pollination?

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  • Question 19

    During his studies on genes in Drosophila that were sex-linked T.H. Morgan found F2 − population phenotypic ratios deviated from expected 9:3:3:1. Explain the conclusion he arrived at.

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  • Question 20

    Describe the termination process of transcription in bacteria.

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  • Question 21

    How does RNA interference help in developing resistance in tobacco plant against nematode infection?

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  • Question 22

    Draw a longitudinal section of a post − pollinated Pistil showing entry of pollen tube into a mature embryo-sac. Label filiform apparatus, chalazal end, Hilum, antipodals, male gametes and secondary nucleus.

    OR

    Draw a labelled sectional view of seminiferous tubule of a human male.

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  • Question 23

    Explain the efforts which must be put in to improve health, hygiene and milk yield of cattle in a dairy farm.

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  • Question 24

    Explain convergent and divergent evolution with the help of one example of each.

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  • Question 25

    Eco RI is used cut a segment of foreign DNA and that of a vector DNA to form a recombinant DNA. Show with the help of schematic diagrams.

    (i)The set of palindronic nucleotide sequence of base pairs the Eco RI will recognise in both the DNA segments. Mark the site at which Eco RI will act and cut both the segments.

    (ii)Sticky ends formed on both the segments where the two DNA segments will join later to form a recombinant DNA.

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  • Question 26

    An antibody molecule is represented as H2L2. Explain.

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  • Question 27

    Identify a, b, c, d, e and f in the table given below:

    Organism

    Bioactive molecule

    Use

    1.

    Monascus perpureus (Yeast)

    2.

    Antibiotic

    3.

    Cyclosporin A

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  • Question 28

    When and where are primary oocytes formed in a human female? Trace the development of these oocytes till ovulation (in menstrual cycle). How do gonadotropins influence this developmental process?

    OR

    (a)Explain the events taking place at the time of fertilization of an ovum in a human female.

    (b)Trace the development of zygote upto its implantation in the uterus.

    (c)Name and draw a labelled sectional view of the embryonic stage that gets implanted.

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  • Question 29

    Draw and explain a logistic curve for a population of density (N) at time (t) whose intrinsic rate of natural increase is (r) and carrying capacity is (k).

    OR

    Describe the process of decomposition of detritus under the following heads: Fragmentation; leaching; catabolism; humification and mineralization.

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  • Question 30

    Write the symptoms of haemophilia and sickle-cell anaemia in humans.

    Explain how the inheritance pattern of the two diseases differ from each other.

    OR

    (a) Write Hardy-Weinberg principle.

    (b) Explain the three different ways the natural selection can affect the frequency of a heritable trait in a population shown in the graph given below.

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