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DELHI PUBLIC SCHOOL, SILIGURI Pre-Board examination Session: 2020- 21 CLASS: XII SC Subject: Biology Time: 60 Minutes DATE : 15/01/2021 Descriptive Max. Marks :30 General Instructions: (i) All questions are compulsory. (ii) The question paper has four sections: Section A, Section B, Section C and Section D. There are 33 questions in the question paper. (iii) Section A has 5 questions of 1 mark each. Section B has 4 questions of 2 marks each. Section C has 4 questions of 3 marks each and Section D has 1 question of 5 marks. (iv) There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions. (v) Wherever necessary, neat and properly labeled diagrams should be drawn. SECTION- A (1X5= 5) Q1.Give an example of a chromosomal disjunction of autosomes. disorder caused due to non(1) Q2.The gene I that controls the ABO blood grouping in human beings has three alleles IA, IB and i. (i) How many different genotypes are likely to be present in the human population? (ii) Also, how many phenotypes are possibly present? ( + =1) Q3. Why are some seeds of Citrus referred to as poly embryonic? How are they formed? (1) Q4. What makes the Nucleopolyhedrovirus a desirable biological control agent? OR What are flocs formed during secondary treatment of sewage? (1) Q5. About 200 species of Cichlid fish became extinct when a particular fish was introduced in Lake Victoria of Africa. Name the invasive fish. (1) SECTION- B (2 x 4 = 8) Q6. Hot-spots occupy less than 2% of earth s land surface. Yet, they are given priority for conservation of biodiversity. Give two reasons for this. (2)
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