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Board Paper of Class 12-Science 2014 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
    Write the name of the organism that is referred to as the 'Terror of Bengal'. VIEW SOLUTION
  • Question 2
    What are 'true breeding lines' that are used to study inheritance pattern of traits in plants? VIEW SOLUTION
  • Question 3
    Name any two types of cells that act as 'cellular barriers' to provide innate immunity in humans. VIEW SOLUTION
  • Question 4
    Mention the type of host cells suitable for the gene guns to introduce an alien DNA. VIEW SOLUTION
  • Question 5
    How is 'stratification' represented in a forest ecosystem? VIEW SOLUTION
  • Question 6
    Give an example of an organism that enters 'diapause' and why. VIEW SOLUTION
  • Question 7
    Identify 'a' and 'b' in the figure given below representing proportionate number of major vertebrate taxa.
    VIEW SOLUTION
  • Question 8
    State the cause of accelerated eutrophication. VIEW SOLUTION
  • Question 9
    Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions? VIEW SOLUTION
  • Question 10
    A cross was carried out between two pea plants showing the contrasting traits of height of the plants. The result of the cross showed 50% parental characters.
    (i) Work out the cross with the help of a Punnett square.
    (ii) Name the type of the cross carried out. VIEW SOLUTION
  • Question 11
    How does the gene 'I' control ABO blood groups in humans ? Write the effect the gene has on the structure of red blood cells.
     
    OR

    Write the types of sex-determination mechanisms the following crosses show. Give an example of each type.
    (i) Female XX with Male XO
    (ii) Female ZW with Male ZZ VIEW SOLUTION
  • Question 12
    (i) Name the scientist who suggested that the genetic code should be made of a combination of three nucleotides.
    (ii) Explain the basis on which he arrived at this conclusion. VIEW SOLUTION
  • Question 13
    State the disadvantage of inbreeding among cattle. How it can be overcome? VIEW SOLUTION
  • Question 14
    Explain with the help of a suitable example the naming of a restriction endonuclease. VIEW SOLUTION
  • Question 15
    State how has Agrobacterium tumifaciens been made a useful cloning vector to transfer DNA to plant cells. VIEW SOLUTION
  • Question 16
    Construct an age pyramid which reflects a stable growth status of human population. VIEW SOLUTION
  • Question 17
    Apart from being a part of the food chain, predators play other important roles. Mention any two such roles supported by examples. VIEW SOLUTION
  • Question 18
    How are 'sticky ends' formed on a DNA strand? Why are they so called? VIEW SOLUTION
  • Question 19
    Explain any three advantages that seeds offer to angiosperms. VIEW SOLUTION
  • Question 20
    Name and explain the role of the inner and middle walls of the human uterus. VIEW SOLUTION
  • Question 21
    A colour-blind child is born to a normal couple. Work out a cross to show how it is possible. Mention the sex of this child.
    ‚Äč
    OR

    Mendel published his work on inheritance of characters in 1865, but it remained unrecognised till 1900. Give three reasons for the delay in accepting his work. VIEW SOLUTION
  • Question 22
    Women are often blamed for producing female children. Consequently, they are ill-treated and ostracised. How will you address this issue scientifically if you were to conduct an awareness programme to highlight the values involved? VIEW SOLUTION
  • Question 23
    (a) Name the tropical sugar cane variety grown in South India. How has it helped in improving the sugar cane quality grown in North India?
    (b) Identify 'a', 'b' and 'c' in the following table:
    No. Crop Variety Insect Pests
    1. Brassica Pusa Gaurav    (a)   
    2. Flat bean Pusa Sem 2
    Pusa Sem 3
       (b)  
     
    3.    (c)   Pusa Sawani
    Pusa A-4
    Shoot and Fruit borer
    VIEW SOLUTION
  • Question 24
    Why are beehives kept in a crop field during flowering period? Name any two crop fields where this is practised. VIEW SOLUTION
  • Question 25
    How did the process of RNA interference help to control the nematode from infecting the roots of tobacco plants? VIEW SOLUTION
  • Question 26
    Study the graph given below and answer the questions that follow :


    (i) Write the status of food and space in the curves (a) and (b).
    (ii) In the absence of predators, which one of the two curves would appropriately depict the prey population?
    (iii) Time has been shown on X-axis and there is a parallel dotted line above it. Give the significance of this dotted line. VIEW SOLUTION
  • Question 27
    (i) What is primary productivity ? Why does it vary in different types of ecosystems?
    (ii) State the relation between gross and net primary productivity. VIEW SOLUTION
  • Question 28
    (a) Coconut palm is monoecious, while date palm is dioecious. Why are they so called?
    (b) Draw a labelled diagram of sectional view of a mature embryo sac of an angiosperm.

    OR
     
    (a) How is 'oogenesis' markedly different from 'spermatogenesis' with respect to the growth till puberty in the humans?
    (b) Draw a sectional view of human ovary and label the different follicular stages, ovum and Corpus luteum. VIEW SOLUTION
  • Question 29
    (a) Explain the process of DNA replication with the help of a schematic diagram.
    (b) In which phase of the cell cycle does replication occur in Eukaryotes? What would happen if cell-division is not followed after DNA replication.
    OR

    (a) Explain Darwinian theory of evolution with the help of one suitable example. State the two key concept of the theory.
    (b) Mention any three characteristics of Neanderthal man that lived in near east and central Asia. VIEW SOLUTION
  • Question 30
    (a) Name the technology that has helped scientists to propagate on a large scale the desired crops in a short duration. List the steps carried out to propagate the crops by the said technique.
    (b) How are somatic hybrids obtained?
    OR

    (a) Cancer is one of the most dreaded diseases. Explain 'Contact inhibition' and 'Metastasis' with respect to the disease.
    (b) Name the group of genes that have been identified in normal cells that could lead to cancer. How do these genes cause cancer?
    (c) Name any two techniques that are useful in detecting cancers of internal organs.
    (d) Why are cancer patients often given α-interferon as part of the treatment? VIEW SOLUTION
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