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CBSE / NCERT Class 12 Biology Practice Question Papers

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Brain Grain · braingrain.in
Biology — Practice Paper · Set 1
Class: 12CBSE / NCERTMax Marks: 34
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 6 × 1 = 6

Choose the correct answer. (Answer all questions.)

1.Select the statement which explains best parasitism.a. One organism is benefited.b. Both the organisms are benefited.c. One organism is benefited, other is not affected.d. One organism is benefited, other is affected.[1]
2.What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation? (a) 100% (b) 50 % (c) 1-5% (d) 2-10%a. 100%b. 50 %c. 1-5%d. 2-10%[1]
3.Which one of the following has the largest population in a food chain? (a) Producers (b) Primary consumers (c) Secondary consumers (d) Decomposersa. Producersb. Primary consumersc. Secondary consumersd. Decomposers[1]
4.The second trophic level in a lake is (a) Phytoplankton (b) Zooplankton (c) Benthos (d) Fishesa. Phytoplanktonb. Zooplanktonc. Benthosd. Fishes[1]
5.Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because –a. bacteria are resistant to the toxinb. toxin is immaturec. toxin is inactived. bacteria encloses toxin in a special sac[1]
6.Secondary producers are (a) Herbivores (b) Producers (c) Carnivores (d) None of the abovea. Herbivoresb. Producersc. Carnivoresd. None of the above[1]
Part II — Short Answer Questions 14 × 2 = 28

Answer briefly. (Answer all questions.)

7.Explain the role of tapetum in the formation of pollen-grain wall.[2]
8.If the sequence of one strand of DNA is written as follows: 5' -ATGCATGCATGCATGCATGCATGCATGC-3' Write down the sequence of complementary strand in 5'→3' direction.[2]
9.How is a cancerous cell different from a normal cell?[2]
10.If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?[2]
11.What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?[2]
12.Give an account of energy flow in an ecosystem.[2]
13.Why is apple called a false fruit? Which part(s) of the flower forms the fruit?[2]
14.Name the hormones involved in regulation of spermatogenesis.[2]
15.What is menstrual cycle? Which hormones regulate menstrual cycle?[2]
16.Define ecological pyramids and describe with examples, pyramids of number and biomass.[2]
17.Depending upon the chemical nature of the template (DNA or RNA) and the nature of nucleic acids synthesised from it (DNA or RNA), list the types of nucleic acid polymerases.[2]
18.Group the following as nitrogenous bases and nucleosides: Adenine, Cytidine, Thymine, Guanosine, Uracil and Cytosine.[2]
19.Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).[2]
20.With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.[2]
🔑 Show Answer Key — Set 1
  1. 1. (d) One organism is benefited, other is affected.
  2. 2. (b) 50 %.
  3. 3. (d) Decomposers.
  4. 4. (b) Zooplankton.
  5. 5. (c) toxin is inactive.
  6. 6. (d) None of the above.
  7. 7. Tapetum nourishes developing microspores and supplies materials, enzymes and precursors needed for pollen wall formation, including sporopollenin precursors.
  8. 8. The complementary strand in 5' to 3' direction is 5'-GCATGCATGCATGCATGCATGCATGCAT-3'.
  9. 9. A cancerous cell divides uncontrollably, ignores normal growth regulation, can invade surrounding tissues and may spread to distant sites, unlike a normal cell.
  10. 10. Parthenocarpy would be selected for fruits where seedlessness is desirable, such as banana, grapes, watermelon, orange or tomato.
  11. 11. HIV infects and destroys helper T-lymphocytes, reducing cell-mediated and antibody-mediated immune responses and causing immunodeficiency.
  12. 12. Energy flow in ecosystems is unidirectional: from sun to producers, then to consumers and decomposers, with loss as heat at each transfer.
  13. 13. Apple is called a false fruit because the thalamus also contributes to fruit formation. In true fruits the ovary forms the fruit, while in apple the fleshy edible part develops mainly from the thalamus.
  14. 14. GnRH, LH, FSH, androgens and inhibin regulate spermatogenesis.
  15. 15. The menstrual cycle is the cyclic change in the female reproductive tract, especially ovaries and uterus, that prepares for pregnancy and includes menstruation if fertilisation does not occur. It is regulated by GnRH, FSH, LH, oestrogen and progesterone.
  16. 16. Ecological pyramids are graphical representations of trophic relationships in terms of number, biomass or energy.
  17. 17. The types are DNA-dependent DNA polymerase, DNA-dependent RNA polymerase, RNA-dependent RNA polymerase and RNA-dependent DNA polymerase.
  18. 18. Nitrogenous bases: Adenine, Thymine, Uracil and Cytosine. Nucleosides: Cytidine and Guanosine.
  19. 19. Examples include recombinant human insulin, growth hormone, erythropoietin, interferon-alpha, interferon-beta, factor VIII, factor IX, tissue plasminogen activator, hepatitis B vaccine antigen and granulocyte colony-stimulating factor.
  20. 20. A typical angiosperm ovule has a funicle, hilum, integuments, micropyle, nucellus, embryo sac, chalaza and often a raphe in anatropous ovules.
Brain Grain · braingrain.in
Biology — Practice Paper · Set 2
Class: 12CBSE / NCERTMax Marks: 34
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 6 × 1 = 6

Choose the correct answer. (Answer all questions.)

1.The second trophic level in a lake is (a) Phytoplankton (b) Zooplankton (c) Benthos (d) Fishesa. Phytoplanktonb. Zooplanktonc. Benthosd. Fishes[1]
2.Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because –a. bacteria are resistant to the toxinb. toxin is immaturec. toxin is inactived. bacteria encloses toxin in a special sac[1]
3.Secondary producers are (a) Herbivores (b) Producers (c) Carnivores (d) None of the abovea. Herbivoresb. Producersc. Carnivoresd. None of the above[1]
4.Select the statement which explains best parasitism.a. One organism is benefited.b. Both the organisms are benefited.c. One organism is benefited, other is not affected.d. One organism is benefited, other is affected.[1]
5.What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation? (a) 100% (b) 50 % (c) 1-5% (d) 2-10%a. 100%b. 50 %c. 1-5%d. 2-10%[1]
6.Which one of the following has the largest population in a food chain? (a) Producers (b) Primary consumers (c) Secondary consumers (d) Decomposersa. Producersb. Primary consumersc. Secondary consumersd. Decomposers[1]
Part II — Short Answer Questions 14 × 2 = 28

Answer briefly. (Answer all questions.)

7.Why do you think the zygote is dormant for sometime in a fertilised ovule?[2]
8.Name the functions of the following: (a) Corpus luteum (b) Endometrium (c) Acrosome (d) Sperm tail (e) Fimbriae[2]
9.Define spermiogenesis and spermiation.[2]
10.What are the measures one has to take to prevent from contracting STDs?[2]
11.Briefly describe the following: (a) Transcription (b) Polymorphism (c) Translation (d) Bioinformatics[2]
12.What are transgenic bacteria? Illustrate using any one example.[2]
13.What are Cry proteins? Name an organism that produce it. How has man exploited this protein to his benefit?[2]
14.Do you think that reproductive health in our country has improved in the past 50 years? If yes, mention some such areas of improvement.[2]
15.Is the use of contraceptives justified? Give reasons.[2]
16.The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT (b) CMI (c) AIDS (d) NACO (e) HIV[2]
17.Draw a labelled diagram of a Graafian follicle.[2]
18.Do eukaryotic cells have restriction endonucleases? Justify your answer.[2]
19.Identify True/False statements. Correct each false statement to make it true. (a) Androgens are produced by Sertoli cells. (b) Spermatozoa get nutrition from Sertoli cells. (c) Leydig cells are found in ovary. (d) Leydig cells synthesise androgens. (e) Oogenesis takes place in corpus luteum. (f) Menstrual cycle ceases during pregnancy. (g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.[2]
20.Amniocentesis for sex determination is banned in our country. Is this ban necessary? Comment.[2]
🔑 Show Answer Key — Set 2
  1. 1. (b) Zooplankton.
  2. 2. (c) toxin is inactive.
  3. 3. (d) None of the above.
  4. 4. (d) One organism is benefited, other is affected.
  5. 5. (b) 50 %.
  6. 6. (d) Decomposers.
  7. 7. The zygote remains dormant for some time so that endosperm can develop first and provide nourishment for embryo development.
  8. 8. (a) Corpus luteum secretes progesterone. (b) Endometrium supports implantation and pregnancy. (c) Acrosome contains enzymes that help sperm penetrate the ovum. (d) Sperm tail provides motility. (e) Fimbriae help collect the ovum after ovulation.
  9. 9. Spermiogenesis is the transformation of spermatids into spermatozoa. Spermiation is the release of spermatozoa from Sertoli cells into the lumen of seminiferous tubules.
  10. 10. One should avoid sex with unknown or multiple partners, use condoms during coitus, and consult a qualified doctor for early detection and complete treatment if infection is suspected.
  11. 11. (a) Transcription is synthesis of RNA from a DNA template. (b) Polymorphism is heritable genetic variation present in a population at appreciable frequency. (c) Translation is synthesis of a polypeptide from the codon sequence of mRNA. (d) Bioinformatics is the use of computational tools to store, retrieve and analyse biological data.
  12. 12. Transgenic bacteria are bacteria whose DNA has been genetically modified by introducing a foreign gene. An example is E. coli engineered to produce human insulin.
  13. 13. Cry proteins are insecticidal proteins encoded by cry genes of Bacillus thuringiensis. Humans have used these genes to develop pest-resistant transgenic crops such as Bt cotton.
  14. 14. Yes. Improvement is shown by better awareness, more medically assisted deliveries, better post-natal care, reduced maternal and infant mortality, small-family acceptance, improved STI detection and treatment, and wider medical facilities.
  15. 15. Yes, contraceptive use is justified when used responsibly to prevent unwanted pregnancy, delay or space pregnancies, and help control unchecked population growth.
  16. 16. (a) Mucosa-associated lymphoid tissue. (b) Cell-mediated immunity. (c) Acquired Immuno Deficiency Syndrome. (d) National AIDS Control Organisation. (e) Human Immunodeficiency Virus.
  17. 17. A correct labelled diagram should show secondary oocyte, zona pellucida, corona radiata, antrum, granulosa cells, theca interna, theca externa and cumulus oophorus.
  18. 18. No, restriction endonucleases are known mainly from prokaryotes, where they protect cells by cutting invading foreign DNA.
  19. 19. (a) False. (b) True. (c) False. (d) True. (e) False. (f) True. (g) True.
  20. 20. Yes. The ban is necessary because misuse of amniocentesis for sex determination can lead to female foeticide.
Brain Grain · braingrain.in
Biology — Practice Paper · Set 3
Class: 12CBSE / NCERTMax Marks: 34
Name: ____________________Reg No: ____________
Part I — Multiple Choice Questions 6 × 1 = 6

Choose the correct answer. (Answer all questions.)

1.Select the statement which explains best parasitism.a. One organism is benefited.b. Both the organisms are benefited.c. One organism is benefited, other is not affected.d. One organism is benefited, other is affected.[1]
2.What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation? (a) 100% (b) 50 % (c) 1-5% (d) 2-10%a. 100%b. 50 %c. 1-5%d. 2-10%[1]
3.Which one of the following has the largest population in a food chain? (a) Producers (b) Primary consumers (c) Secondary consumers (d) Decomposersa. Producersb. Primary consumersc. Secondary consumersd. Decomposers[1]
4.The second trophic level in a lake is (a) Phytoplankton (b) Zooplankton (c) Benthos (d) Fishesa. Phytoplanktonb. Zooplanktonc. Benthosd. Fishes[1]
5.Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because –a. bacteria are resistant to the toxinb. toxin is immaturec. toxin is inactived. bacteria encloses toxin in a special sac[1]
6.Secondary producers are (a) Herbivores (b) Producers (c) Carnivores (d) None of the abovea. Herbivoresb. Producersc. Carnivoresd. None of the above[1]
Part II — Short Answer Questions 14 × 2 = 28

Answer briefly. (Answer all questions.)

7.Which property of DNA double helix led Watson and Crick to hypothesise semi-conservative mode of DNA replication? Explain.[2]
8.Find out the role of microbes in the following and discuss it with your teacher. (a) Single cell protein (SCP) (b) Soil[2]
9.Differentiate between: (a) hypocotyl and epicotyl; (b) coleoptile and coleorrhiza; (c) integument and testa; (d) perisperm and pericarp.[2]
10.List the attributes that populations possess but not individuals.[2]
11.Describe briefly the following: (a) Origin of replication (b) Bioreactors (c) Downstream processing[2]
12.If a double stranded DNA has 20 per cent of cytosine, calculate the per cent of adenine in the DNA.[2]
13.Draw a labelled diagram of sperm.[2]
14.How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?[2]
15.Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?[2]
16.Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.[2]
17.Who had proposed the chromosomal theory of inheritance?[2]
18.Find out the name of the microbes from which Cyclosporin A (an immunosuppressive drug) and statins (blood cholesterol lowering agents) are obtained.[2]
19.Name important defence mechanisms in plants against herbivory.[2]
20.In which food would you find lactic acid bacteria? Mention some of their useful applications.[2]
🔑 Show Answer Key — Set 3
  1. 1. (d) One organism is benefited, other is affected.
  2. 2. (b) 50 %.
  3. 3. (d) Decomposers.
  4. 4. (b) Zooplankton.
  5. 5. (c) toxin is inactive.
  6. 6. (d) None of the above.
  7. 7. The complementary base pairing of the two antiparallel DNA strands led Watson and Crick to hypothesise semi-conservative replication.
  8. 8. (a) Microbes are grown as protein-rich biomass called single cell protein for food or feed. (b) In soil, microbes decompose organic matter, recycle nutrients, fix nitrogen, form mycorrhizae and improve fertility.
  9. 9. (a) Hypocotyl is the embryonic axis below the cotyledons; epicotyl is above the cotyledons. (b) Coleoptile protects the plumule; coleorrhiza protects the radicle. (c) Integuments are ovule coverings; testa is the seed coat formed from integuments. (d) Perisperm is persistent nucellus; pericarp is the fruit wall formed from the ovary wall.
  10. 10. Populations possess birth rate, death rate, sex ratio, age distribution and population density; individuals do not possess these attributes as population-level properties.
  11. 11. (a) Origin of replication is the DNA sequence where replication starts. (b) Bioreactors are vessels that provide optimal conditions for large-scale biological production. (c) Downstream processing includes separation, purification, formulation and quality testing of a biotechnological product.
  12. 12. The DNA has 30 per cent adenine.
  13. 13. A correct labelled diagram should show head, acrosome, nucleus, neck, middle piece with mitochondria, tail and plasma membrane.
  14. 14. Six eggs were most likely released.
  15. 15. Plants and other biotic components control floods and soil erosion by intercepting rainfall, binding soil with roots, improving water infiltration and reducing surface runoff.
  16. 16. In DNA vaccines, a suitable gene is a gene from the pathogen that codes for an antigenic protein capable of inducing a protective immune response without causing disease.
  17. 17. Walter Sutton and Theodore Boveri proposed the chromosomal theory of inheritance.
  18. 18. Cyclosporin A is obtained from Trichoderma polysporum, and statins are obtained from Monascus purpureus.
  19. 19. Important plant defences include morphological defences such as thorns and chemical defences such as toxic, distasteful or digestion-inhibiting compounds.
  20. 20. Lactic acid bacteria are found in curd. They convert milk into curd, improve nutritional quality by increasing vitamin B12, and help check disease-causing microbes in the stomach.

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