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CBSE Class 12 Pre Board 2019 : Biology - Prelim 1 (St Xavier's Sr. Sec. School, Delhi)

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Pre Board Examination 2019 Std. 12 03-01-2019 Set 1 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 organism and the mode of reproduction represented in the diagram given below. (1) (OR) Banana crop is produced by farmers without sowing of seeds. Explain how the plant is propagated? (1) 2. Which group of organisms, regulators or conformers, can show maximum functional efficiency regardless of the existing weather conditions? Why? (1) 3. Which one of the following is used in apiculture Hilsa, Apis indica, Sonalika? (1) 4. A multinational company outside India tried to sell new varieties of turmeric without proper patent rights. What is such an act referred to? (1) 5. Why is proinsulin so called? How is insulin different from it? (OR) Why is it not possible for an alien DNA to become part of a chromosome anywhere along its length and replicate normally? (1) (1) SECTION B 6. Why should a bisexual flower be emasculated and bagged prior to artificial pollination? (2) 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. A boy of ten years had chickenpox. He is not expected to have the same disease for the rest of life. Mention how it is possible. OR It was diagnosed by a specialist that the immune system of the body of a patient has been suppressed. Name the disease the patient is suffering from and its causative agent. (2) (2) Std. 12 9. BIOLOGY (Set 1) 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. (2) (OR) State the use of following enzymes/acids produced by the microbes i) Lipase ii) Lactic acid iii) streptokinase iv) pectinase (2) 10. Explain palindromic nucleotide sequence with the help of a suitable example. Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples. 11. Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples. 12. How are assisted reproductive technologies helpful to humans? How are ZIFT and different from intra uterine transfers? Explain. (2) SECTION C 13. Explain the phenomenon of double fertilization. (OR) Draw a well labeled diagram of MICROSPOROGENESIS. 14. The base sequence in one of the strands of DNA is TAGCATGAT. i) Give the base sequence of the complementary strand. ii) How are these base pairs held together in a DNA molecule? iii) Explain the base complementarity rule. Name the scientist who framed this rule. (OR) In a Mendelian Monohybrid cross, the F2 generation shows identical genotypic and phenotypic ratios. What does it tell us about the nature of the alleles involved? Justify your answer. Std. 12 15. BIOLOGY (Set 1) Page 3 How are the structural genes activated in lac operon in coli? OR 16. What are the factors that support Darwin s theory of Natural selection? 17. i) ii) iii) 18. Mention the property of plant cells that has helped them to grow into a new plant in in vitro Explain the advantages of micro propagation. 19. The diagram here is that of a typical biogas plant. Explain the sequence of events occurring in a biogas plant. Identify A, B and C. 20. i) ii) 21. Explain the effect of deletion of the gene for ADA in an individual. How does the gene therapy help in this case? 22. i) ii) Name the causative agent of typhoid in humans. Name the test administered to confirm the disease. How does the pathogen gain entry into the human body? Write the diagnostic symptoms and mention the body organ that gets affected in severe cases? (OR) Why is using tobacco in any form injurious to the health? Explain. Why are restriction endonucleases, so called? What is a palindromic, nucleotide sequence? How do restriction endonucleases act on palindromic sites, to create sticky ends? Why are small animals rarely found in the Polar Regions? Explain. Bear hibernates, whereas some species of zooplanktons enter diapause to avoid stressful external conditions. Std. 12 BIOLOGY (Set 1) Page 4 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. 24. i) ii) iii) When and how does placenta develop in human female? How is the placenta connected to the embryo? Placenta acts as an endocrine gland. Explain. SECTION D 25. How does the megaspore mother cell develop into 7-celled and 8-nucleate embryo sac in an angiosperm? Draw a labeled diagram of a mature embryo sac. (OR) Draw a diagram of human sperm. Label only those parts along with their functions that assist the sperm to reach and gain entry into the female gamete. 26. Answer the following questions based on Meselson and Stahl s experiment: i) Write the name of the chemical substance used as a source of nitrogen in the experiment by them. ii) Why did the scientists synthesize the light and the heavy DNA molecules in the organism used in the experiment? iii) How did the scientists make it possible to distinguish the heavy DNA molecule from the light DNA molecule? Explain. iv) Write the conclusion the scientists arrived at, after completing the experiment. (OR) What is striking difference between Mendelian inheritance, polygenic inheritance and pleiotropy? 27. i) ii) Differentiate between primary and secondary ecological successions. Explain the different steps of xerarch succession occurring in nature. (OR) Explain four evil-quartets which cause depletion of biodiversity. -x-x-x-x-x-x-

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