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CBSE Class 12 Pre Board 2019 : Biology - Prelim 2 (St Xavier's Sr. Sec. School, Delhi)

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Pre Board Examination 2019 Std. 12 03-01-2019 Set 2 BIOLOGY Max. Marks : 70 Time : 3 hrs. General Instructions: All questions are compulsory. The question paper consists of four sections A, B, C and D. Internal choice is given in all the sections. A student has to attempt only one of the alternatives in such questions. Section A contains 5 questions of 1 mark each. Section B has 7 questions of 2 marks each. Section C is of 12 questions of 3 marks each Section D has 3 questions of 5 marks each. Wherever necessary, the diagrams drawn should be neat and properly labeled. SECTION A 1. Name the site of fertilization in humans? (OR) The meiocyte of rice has 24 chromosomes. How many chromosomes are present in endosperm of rice? (1) 2. Name the Organism commercially used for the production of single cell protein. (1) 3. What is brood parasitism? (1) 4. Why must a cell be made 'competent' in biotechnology experiments? How does calcium ion help in doing so? (OR) State the role of 'Biolistic gun' in biotechnology experiments. 5. What are the 'molecular scissors' in rDNA technology? What are they used for in rDNA technology? (1) (1) (1) SECTION B 6. What are staminate and pistillate flowers? Name the types of gametes that are formed in staminate and pistillate flowers? 7. Prior to industrialization, there were far more white-winged moths on trees than melanised moths in England. However, after industrialization, the distribution pattern of these two kinds of moths reversed. What does the above observation indicate? Explain giving reasons. (2) 8. What kind of test will you perform to find out whether the given plant is homozygous dominant or heterozygous? Explain your answer with the help of cross. 9. Expand ELISA and LSD? Explain very briefly. (OR) Name the enzyme produced by streptococcus bacterium. Explain its importance in medical sciences. (2) 10. Differentiate between primary and secondary succession. Provide one example of each. (2) 11. What problem was faced in production of insulin by rDNA technology and how was it resolved? (2) (2) (2) (2) Std. 12 12. BIOLOGY (Set 2) Page 2 Study the flow chart given below: Identify the events that take place at stages A and B , state the importance of the technology explained above. (OR) State the use of following enzymes/acids produced by the microbes i) Lipase ii) lactic acid iii) streptokinase iv) pectinase (2) SECTION C 13. Describe the mechanism the prevent polyspermy in human. (OR) How are assisted reproductive technologies helpful to humans? How are ZIFT and GIFT different from intra uterine transfers? Explain. (3) (3) 14. In Snapdragon, A cross between true breeding red flower (RR) plants and true breeding white flower (rr) plants showed a Progeny of plants with all pink flowers. (a) The appearance of pink flowers is not known as blending. Why? (b) What is the phenomenon known as? (3) (OR) Explain the given phenomenon with an adequate example. (3) 15. Name the major types of RNAs and explain their role in the process of protein synthesis. 16. A couple has four daughters. The man blames the woman for giving birth to daughters. His wife is pregnant for the fifth time, as the couple wants at least one son. a) What is the probability of this couple getting a son this time, sure or only a chance? b) Who is responsible for the birth of daughters to them? c) What values are insisted by convincing him to stop producing more children? (3) (OR) Give two reasons why both the strands of DNA are not copied during transcription. (3) 17. Draw a well labeled diagram of the following:Microsporogenesis in plants. (3) (3) Std. 12 18. a) b) c) BIOLOGY (Set 2) Page 3 Name the respective forms in which the malarial parasite gains entry into i) Human body and ii) Body of female Anopheles Name the hosts where the sexual and the asexual reproduction of malarial parasite occur respectively. Name the toxin responsible for the appearance of symptoms of malaria in humans. Why do these symptoms occur periodically? 19. Explain the points that have to be considered for successful bee- keeping? 20. a) b) 21. a) b) (3) Expand BOD. At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organism in this part of the river? c) Under what conditions will the BOD are lowered in the river? How will it affect the aquatic life? (OR) An active member of an awareness group conducts regular programmes to sensitize public against alcoholism amongst youth as a serious health hazard in his locality. Identify the values this member of the group is trying to propagate amongst the people in his locality. Why are restriction endonucleases, so called? What is a palindromic, nucleotide sequence? How do restriction endonucleases act on palindromic sites, to create sticky ends? (3) 22. What is RNA interference? Mention its role in production of pest resistant plants. (3) 23. By the end of 2002, the public transport of Delhi switched over to a new fuel. Name the fuel. Why is this fuel considered better? Explain. (3) 24. Study the given aquatic food chain and answer the questions that follow: Water (DDT 0.003ppm) -----> Zooplankton (DDT 0.04 ppm) -------> Small fish (DDT 0.5 ppm) -----> Large Fish (DDT 2ppm) ----------> Fish eating Birds (DDT 5 ppm) a) b) c) Explain why there is a continuous increase in DDT content in different trophic levels of the chain. Name the phenomenon responsible for the increase in DDT content. How does this phenomenon disturbs the metabolism of birds? (3) SECTION D 25. Explain the ovarian and uterine events that occur during a menstrual cycle in a human female under the influence of pituitary and ovarian hormones, respectively. (OR) The following is the illustration of the sequence of ovarian events A to I in a human female : (5) Std. 12 a) b) c) d) 26. BIOLOGY (Set 2) Page 4 Identify the figures that illustrate corpus leutem and name the pituitary hormone that influences its formation. Specify the endocrine function of corpus luteum. How does it influence the uterus? Why is it essential? What is the difference between D and E? Draw a neat labeled sketch of Graafian follicle. Explain the given Diagram in detail: (OR) Answer the following questions based on Meselson and Stahl s experiment. a) Write the name of the chemical substance used as a source of nitrogen in the experiment by them. b) Why did the scientists synthesize the light and the heavy DNA molecules in the organism used in the experiment? c) How did the scientists make it possible to distinguish the heavy DNA molecule from the light DNA molecule? Explain. d) Write the conclusion the scientists arrived at, after completing the experiment. 27. (5) a) b) a) b) (5) With suitable examples, explain the energy flow through different trophic levels. What does each bar in this pyramid represent? Write any two limitations of ecological pyramids. (5) (OR) Why herbivores are considered similar to predators in the ecological context? Explain. Differentiate between the following interspecific interactions in a population: i) Mutualism and competition ii) Commensalism and amensalism. -x-x-x-x-x-x-

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