2018 CBSE BIOLOGY MODEL QUESTION PAPER WITH ANSWERS GENERAL INSTRUCTIONS:-1. All questions are compulsory.2. This question paper consists of four sections A,B,C and D . 3.Section A consists of 5 questions which are very short type carrying 1 mark each to be answered in one word or one sentence.4. Section B consists of 7 questions which are shot answer type carrying 2 marks each to be answered in about 20-40 words each. 5. Section C consists of 12 questions which are also short answer type carrying 3 marks each to be answered in about 40-60 words each.6.Section D consists of 3 questions which is a long answer type carrying 5 marks each and to be answered in about 80-100 words .3. There is no overall choice. However an internal choice has been provided in two questions of one mark, two questions of two marks, four questions of three marks and all the three questions of five marks weightage. A student has to attempt only one of the alternatives in such questions. 4. Wherever necessary, the diagrams drawn should be neat and properly labeled.

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SECTION-A

1. How do monocytes act as a cellular barrier in humans in providing innate immunity?2. Write the sex of a human having XXY chromosome with 22 pairs of autosomes.3. Write one advantage and one disadvantage of cleistogamy to flowering plants.4. Why do DNA fragments move towards the anode during gel electrophoresis?5. Name one amino acid, which is coded by only one codon

SECTION-B 6. Differentiate between out-crossing and cross breeding

OR Why are microbes like Spirulina produced on a commercial scale? Mention its two advantages.

7. Why is the structure of an antibody molecule represented as H2L2? Name any two types of antibodies produced in a human body.

8. (a) Why do organisms like algae and fungi shift from asexual mode of reproduction to sexual mode? (b) What is a juvenile phase in organism?

9.

Identify the areas in the pie chart representing the biodiversity of plants showing their proportionate number of species of major taxa.

10. A haemophilic father can never pass the gene for haemophilia to his son. Explain.11. (a) What are transgenic animals?

(b) Name the transgenic animal having the largest number amongst all the existing transgenic animals. (c) Mention any three purposes for which these animals are produced.

12. Explain three steps involved in PCR.

SECTION-C

13. Name the three RNA polymerases found in eukaryotic cells and mention their functions. OR

Explain the post transcriptional modifications the hn-RNA undergoes in eukaryotic cell.14. What is biofortification? Mention the contribution of Indian Agricultural Research Institute

towards it with the help of any two examples.15. Why DNA molecule considered as a better hereditary material than RNA molecule?16. Baculoviruses are good example of biocontrol agents. Justify giving three reasons.17. If the meiocyte of a maize plant contains 20 chromosomes, write the number of

chromosomes in the endosperm and embryo of the maize grain and give reasons in support of your answer.

18. Explain, how Eli Lilly, an American company produced insulin by recombinant DNA technology?

19. How can Hardy-Weinberg equilibrium be affected? Explain giving three reasons.20. Explain the ‘Ex-situ conservation’ of biodiversity. How is the in-situ conservation different

from it?21. Do you think apomixes can be compared with asexual reproduction? Support your answer,

giving one reason. How is apomixis beneficial to farmers? Explain.22. Name the product produced and mention their use from the microbes given below.

(a) Aspergillus niger (b) Trichoderma polysporum (c) Monascuc perpureus

23. (a) Draw the diagram of the adult human female reproductive system and label the different: (i) Parts of fallopian tube(ii) Layers of uterine wall

(b) Explain the events during fertilisation of an ovum in humans.OR

(a) Describe a diagrammatic sketch of a T S of an anther of an angiosperm. (b) Describe the process of microsporogenesis up to the formation of microspores.

(c) Write the function of ‘germ pore’ in a pollen grain of an angiosperm

24. (a) The graph given below represents the organism’s response to temperature as an environmental condition. (i) Which one of the two lines represent conformers and why? (ii) (ii) What does the other line in the graph represent and why?

(b) Mention the different adoptions the parasites have evolved with, to be able to successfully complete their life cycle in their hosts.

OR

Draw the pyramid of biomass in sea and in a forest. Explain giving reasons why are the two pyramids different?

SECTION-D.

25. (A) Why does DNA replication in small replication fork? (b) Why is DNA replication continuous and discontinuous in a replication fork? (c) State the importance of origin of replication in a replication fork.

OR What is an operon? Explain the functioning of lac operon when in an open state.

26. Describe the various steps of Griffith’s experiment that led to the conclusion of the ‘Transforming Principle’. How did the nature of the ‘Transforming Principle’ get established?

OR (a)Write the different components of lac-operon. (b) Explain its expression while in an ‘open’ state.

27. (a) Where does fertilisation occur in humans? Explain the events that occur during this process.

(b) A couple where both husband and wife are producing functional gametes, but the wife is still unable to conceive, is seeking medical aid. Describe any one method that you can suggest to this couple to become happy parents.

OR(a) Draw a diagrammatic sectional view of a human seminiferous tubule, and label

sertoli cells, primary spermatocyte, spermatogonium and spermatozoa in it.(b) Explain the hormonal regulation of the process of spermatogenesis in humans.

ANSWER

1. Phagocytosis of microbes or destroy microbes2. Male, klinefelter’s syndrome3. Advantage: assured seed set or maintains pure lines, disadvantage: no variation, only

parental characters are preserved, it can lead to inbreeding depression4. DNA fragments are negatively charged5. Methionine or tryptophan6.

Out-crossing Cross breedingMating of animals of same breed Superior males of one breeding mated with

superior females of another breedNo common ancestors on either side up to 4-6 generations

Progeny may have desirable characters of both parent

Helps to overcome inbreeding depression Used for commercial production or obtaining improved characters

OR(i) As source of food protein(ii) Reduces environmental pollution, solves problem of hunger and malnutrition, rich

source of protein, low cost production7. (a) Two light small polypeptide chain and two heavy longer polypeptide chains. (b) IgA, IgM,

IgE, IgG8. (a) To tide over adverse condition

(b) A phase of growth and maturity, before organism cn reproduce sexually.9. (i) lichen, (ii) algae, (iii) fungi, (iv) mosses10. It is a sex linked recessive disorder in which X-chromosome has the haemophilic gene. Son

inherits a Y chromosome from father and gene for haemophilia is not present on Y chromosome.

11. (a) Animals that have had their DNA manipulated to possess and express an extra foreign gene. (b) Mice (c) (i) Normal physiology and development(ii) Study of disease

(iii) biological products,(iv) vaccine safetyiv) Chemical safety testing.

12. (i) Denaturation: Two strands of DNA are separated by heating. (ii) Annealing: two sets of primers are attached or annealed to the separated DNA strands. (iii) Extention: Taq polymerases catalyses the extention of primer using genomic DNA as template and nucleotides provided in the reaction.

13. (i) RNA polymerase I: transcribes r RNAs (28S, 18S and 5.8S)

(iii) RNA polymerase Ii : transcribes precursor of mRNA(iv) RNA polymerase III : transcribes tRNA or 5sr RNA

OR(i) Splicing: introns are removed and exons are joined (ii) Capping: methyl guanosine triphosphate is added to the 5’ end of hnRNA.(iii) Tailing: polyadenylate residues are added to the 3’ end in a template

independent manner.14. Breeding crops with higher level of vitamins and minerals or higher protein and healthier

fats. E.g. vitamin A enriched carrot or spinach or pumpkin, vitamin C enriched bitter gourd, bathua, mustard and tomato, iron and calcium enriched spinach and bathua, protein enriched broad lablab, French and garden peas.

15. DNA molecule is better genetic material because: (i) presence of thymine instead of uracil (ii) less reactive than RNA due to absence of 2’ OH group (iii) not easily degradable (iv) slow rate of mutation.

16. Species specific, narrow spectrum insecticidal application, no negative impact on plants or mammals or birds or fish or non target insects, beneficial for IPM programme.

17. Endosperm: 30 and embryo: 20.

Diploid meiocyte has 20 chromosomes.haploid gametes have 10 chromosomes. Two haploid gametes fuse together to form a zygote having 10+10= 20 chromosomes. Zygote undergoes mitotic division and gives rise to embryo, so embryo has 20 chromosomes. One haploid gamete carrying 10 chromosomes fuses with two polar nuclei, each carrying 10 chromosomes (haploid) to give rise to endosperm nucleus. So endosperm has 30 chromosomes.i.e. Triploid chromosome.

18. (i) Eli Lilly Company prepared two DNA sequences, corresponding to A and B chains of human insulin.(ii) These chains introduced in the plasmids of E coli to produce insulin chain.

(iii)Chains A and B are produced separately and extracted.

(iv) Two chains combined by creating disulphide bonds.19. (a) Gene migration: when migration of a section of population occurs to another place and

gene frequencies change in the original as well as in the new population. (b) Genetic drift: if the same changes occur by chance, new genes or alleles are added to the new population and these are lost from the old population. (c) Mutation: pre-exiting advantageous mutations when selected will result in new phenotypes. (d) Genetic recombination: variation in characteristics will be there because of genetic recombination during meiosis and due to random fusion of gametes. (e) Natural selection: heritable variations enabling better survival enabled organisms to reproduce and leave greater number of progeny.

20. Ex-situ: threatened animals and plants are taken out from their natural habitat and placed in special settings where they can be protected and given special care, by keeping the gametes of threatened species preserved in viable and fertile conditions for long time. Example: zoological parks, botanical garden, wildlife safari parks, cryopreservation, seed banks, tissue culture etc. In-situ conservation: organisms are given protection in their natural habitat in which biodiversity is protected at all levels.

21. (a) Yes, seeds are produced without fertilisation. (b) Production of hybrid seeds costly. If hybrid seeds with desirable characteristics can be made into apomicts, there is no segregation of characters in the hybrid progeny. Farmer can continue using hybrid seeds year after year not buy new seeds.

22. (a) Aspergillus niger- citric acid, natural preservative or flavouring agent. (b) Trichoderma polysporum- cyclosporine A- immune suppressive agent (c) Monascus purpureus- statin, blood cholesterol lowering agent

23. (a)

(b) When a sperm comes in contact with Zona pellucid of ovum this induces changes in the membrane that blocks entry of additional sperm, secretion of acrosome helps sperm enter into cytoplasm of ovum through zona pellucid and plasma membrane. This induces completion of meiotic division of secondary oocyte and formation of a haploid ootid/ovum and a second polar body. Haploid nucleus of ovum fuses with sperm nucleus to form diploid zygote.

OR

23. (a) T s of anther:

(b) Each cell of sporogenous tissue capable of giving rise to microspore mother cell. Microspore mother cell undergoes meiosis giving rise to microspore tetrad. On maturation and dehydration microspore tetrad forms microspores. (c) Germ pores allow the growing pollen tube with contents of pollen grain (male gametes + vegetative cell) to come out of the pollen.

24. (a) ‘A’ depicts conformers. These organisms which cannot maintain constant internal environment and change according to the ambient atmospheric conditions. They show narrow range of distribution. (b) ‘B’ depicts regulators. These organisms maintain a constant internal environment despite changes in the environment. They show a much wider range of distribution. (c) Loss of unnecessary sense organs, presence of hooks/adhesive organs and suckers, loss of digestive system and high reproductive capacity.

OR

(a) The pyramid of biomass in sea is inverted. Since the biomass of fishes far exceeds than that of phytoplankton, the pyramid is inverted. (b) The pyramid of biomass of forest is erect. Here the produces are at the base. The biomass of producer is much higher than consumer

25. (a) DNA being very long requires high energy for opening its entire length. (b) DNA dependent DNA polymerase catalyses polymerisation in 5’ to 3’ direction. Two strands of DNA are antiparallel and have opposite polarity(c) It is the site where replication originates.

OR(a) The arrangement where a polycistronic structural gene is regulated by a common promoter and regulator gene. (b) lactose acts as inducer, binds with repressor protein. RNA polymerase freely moves over the structural genes, transcribes lac mRNA, which in turn produce enzymes transacetylase, permease, and betagalactosidase responsible for digestion of lactose.

26 Griffith Experiment and establishment of transforming principle 3+2=5OR

2+3=5

OR (a)Components of lac operon (b) correct explanation of open state