Biology 12th Previous Year Question Paper 2017 (CBSE)

Biology

SECTION – A 

(Q. Nos. 1 – 5 are of one marks each) 

Q.1. Name the type of cross that would help to find the genotype of a pea plant bearing violet flowers. 

Answer: Test cross 

 

Q.2. State two postulates of Oparin and Haldane with reference to the origin of life. 

Answer: (i) First form of life could have come from pre-existing non-living organic molecules / RNA & Protein

(ii) Formation of life was preceded by chemical evolution / formation of diverse organic molecules from inorganic constituents.

 

Q.2. Bt -toxins are released as inactive crystals in the bacterial body. What happens to it in

the cotton boll worm body that it kills the boll worm.(SET-III)

Ans: It is converted into an active protein (due to alkaline pH of the gut of the boll worm) , the toxin binds to midgut cells / create pores / causes cell swelling and lysis that kills the bollworm. 

 

Q.3. A herd of cattle is showing reduced fertility and productivity. Provide one reason and one suggestion to overcome this problem. 

Answer: Reason: Inbreeding depression / continuous inbreeding.

Suggestion: Should be mated with unrelated superior cattle of the same breed / out – breeding / out – crossing.

 

Q.3. Name the specific type of gene that is incorporated in a cotton plant to protect the plant against cotton bollworm infestation. (SET-II)

Answer: cry I Ac / cry II Ab

 

Q.4. What are Cry genes ? In which organisms are they present ? 

Ans. The genes which code for Bt toxin / Cry proteins / toxic proteins , Bacillus thuringiensis.

 

Q.5. An electrostatic precipitator in a thermal power plant is not able to generate high voltage of several thousands. Write the ecological implication because of it. 

Answer: Air Pollution // particulate matter / dust particles released in the air.

 

SECTION – B 

(Q Nos. 6-10 are of two marks each) 

Q.6. A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or 3-celled. Explain. How are the cells placed within the pollen grain when shed at a 2-celled stage ? 

Answer: • In 2-celled stage the mature pollen grain contains a generative and vegetative cell, whereas in 3- celled stage one vegetative cell and two male gametes are present.

• The generative cell floats in the cytoplasm of vegetative cell

 

Q.7. Differentiate between the genetic codes given below : 

(a) Unambiguous and Universal 

(b) Degenerate and Initiator 

Answer:  

(a) Unambiguous: One codon codes for only one amino acid. Universal: Genetic code/codons are (nearly) the same for all organisms from bacteria to humans.
(b)Degenerate: More than one codon coding for the same amino acid. Initiator: Start codon / AUG.

 

Q.8. Mention one application for each of the following : 

(a) Passive immunization 

(b) Antihistamine 

(c) Colostrum 

(d) Cytokinin-barrier 

Answer: (a) Provide preformed antibodies / antitoxins for quick response in case of infection by deadly microbes(tetanus) or snake bite.

(b) Reduces symptoms of allergy 

(c) Provides passive immunity / antibodies / Ig A to new born.

(d) Protection of non-infected cells from further viral infection.

 

Q.9. Name the microbes that help production of the following products commercially: 

(a) Statin 

(b) Citric acid 

(c) Penicillin 

(d) Butyric acid 

Answer: (a) Monascus purpureus 

(b) Aspergillus niger 

(c) Penicillium notatum 

(d) Clostridium butylicum 

 

Q.10. List four benefits to human life by eliminating the use of CFCs. 

Answer: (i) Delay in aging of skin 

(ii) Prevent damage to skin cells 

(iii) Prevent skin cancer 

(iv) Prevent snow blindness / inflammation of cornea 

(v) Prevent cataract (a) Unambiguous: 

(vi) Prevents ozone depletion 

(vii) Prevents global warming 

(viii) Reduces greenhouse effect 

(ix) Reduces odd climatic changes or El Nino effect 

OR 

Q.10. Suggest two practices giving one example of each, that help protect rare or threatened species. 

Ans: (1) In situ conservation , biodiversity hotspot / biosphere reserve / national parks /sanctuaries / Ramsar sites / sacred groves (Any one).

(2) Ex situ conservation , Zoological parks / botanical garden / wildlife safari parks / 

cryopreservation techniques / Tissue culture / seed bank / pollen banks.

 

Q.6. Name the type of immunity the colostrum provides to a newborn baby. Write giving an example where this type of immunity should be provided to a person.

Answer: Passive Immunity.

In case of infection by deadly microbes(tetanus) / snake bite where quick immune response is required =1

 

Q.8. Write the binomials of two fungi and mention the products/bioactive molecules they help to produce.

Answer: Trichoderma polysporum , cyclosporin A

Aspergillus niger,citric acid

Monascus purpureus , statin

Saccharomyces cerevisiae, ethanol / alcohol

Penicillium notatum , Penicillin

 

Q.7. Give the binomials of two types of yeast and the commercial bioactive products they help to produce.

Ans: Saccharomyces cerevisiae- ethanol / alcohol Monascus purpureus- statin 

 

Q.9. How many cells are present in the pollen grains at the time of their release from another ? Name the cells.

Ans. Pollen grain may be released at

        2-celled stage , one vegetative and one generative cell ,

        3-celled stage , one vegetative cell and two male gametes 

 

Q.10. Name the group of cells the HIV enters after getting into the human body. What happens in these cells and what are these cells subsequently referred to as ? Name the next group of cells the HIV attacks from here.

Ans. Macrophages , Reverse transcription , HIV Factory , helper T-lymphocytes (TH)

 

SECTION – C 

(Q Nos. 11-22 are of three marks each) 

Q.11. (a) Can a plant flowering in Mumbai be pollinated by pollen grains of the same species growing in New Delhi ? Provide explanations to your answer. 

(b) Draw the diagram of a pistil where pollination has successfully occurred. Label the  parts involved in reaching the male gametes to its desired destination. 

Answer: (a) Yes, By artificial means ( any relevant explanation). 

(b) Diagram with following labellings Stigma , Pollen tube , Synergid / Filiform Apparatus , Micropyle.

 

Q.12. Both Haemophilia and Thalassemia are blood related disorders in humans. Write their causes and the difference between the two. Name the category of genetic disorder they both come under. 

Answer: 

Haemophilia Thalassemia
Single protein involved in the clotting of blood is affected Defects in the synthesis of globin leading to formation of abnormal haemoglobin.
Sex linked reccessive disorder. Autosomal recessive disorder.
Blood does not clot. Results in anaemia.

 

Q.13. (a) List the two methodologies which were involved in human genome project. Mention how they were used. 

(b) Expand ‘YAC’ and mention what was it used for. 

Answer: (a) Expressed Sequence Tags , Identifying all the genes that are expressed as RNA Sequence Annotation , sequencing the whole set of genome coding or non coding sequences and later assigning different region with functions.

(b) Yeast Artificial Chromosome , used as cloning vectors (cloning / amplification ).

 

Q.14. Write the characteristics of Ramapithecus , Dryopithecus and Neanderthal man. 

Answer: Ramapithecus: hairy/ walked like gorillas and chimpanzees , more man like. 

Dryopithecus: hairy/ walked like gorillas and chimpanzees , more ape- like. 

Neanderthal man: brain size is 1400cc , used hides to protect their body / buried their dead.

 

Q.15. Name a human disease, its causal organism, symptoms (any three) and vector, spread by intake of water and food contaminated by human faecal- matter. 

Answer: Amoebiasis (Amoebic dysentery) , Entamoeba histolytica , constipation / abdominal pain / cramps / stools with excess mucus / blood clots (Any three symptoms) , Housefly.

Ascariasis, Ascaris , internal bleeding / muscular pain / fever / anaemia / blockage of intestinal passage (Any three symptoms), Housefly.

Typhoid, Salmonella typhi, high fever / weakness / stomach pain / constipation / headache / loss of appetite (Any three symptoms), Housefly.

OR 

Q.15. (a) Why is there a fear amongst the guardians that their adolescent wards may get 

trapped in drug/alcohol abuse ? 

(b) Explain ‘addiction’ and ‘dependence’ in respect of drug/alcohol abuse in youth. 

Defects in the synthesis of globin leading to formation of abnormal haemeoglobin Sex linked recessive disorder.

Autosomal recessive disorder  Blood does not clot Results in anaemia 

Answer: (a) Adolescents are easily affected by ( vulnerable to) peer pressure /adventure /curiosity / excitement / experimentation / media . 

(b) Addiction -Psychological attachment to certain effects such as Euphoria / temporary feeling of well-being. Dependence-Tendency of the body to show withdrawal syndrome / symptoms if regular doses of drug / alcohol is abruptly discontinued. 

 

Q.16. (a) Write the desirable characters a farmer looks for in his sugarcane crop. 

(b) How did plant breeding techniques help north Indian farmers to develop cane with 

desired characters ? 

Answer: (a) High yield , thick stem,high sugar content , ability to grow in their areas. 

(b) By crossing Saccharum officinarum / south Indian variety having desired characteristics with Saccharum barberi / north Indian low yield variety.

 

Q.17. Secondary treatment of the sewage is also called Biological treatment. Justify this statement and explain the process. 

Answer: Involves biological organism such as aerobic and anaerobic microbes / bacteria and fungi to digest / consume organic waste. 

Primary effluent is passed into aeration tank where vigorous growth of aerobic microbes (flocs) take place, BOD reduced (microbes consume major part of organic matter), effluent is passed to settling tank where flocs sediment to produce activated sludge , sludge is pumped to anaerobic sludge digester to digest bacteria and fungi.

 

Q.18. (a) Explain the significance of ‘palindromic nucleotide sequence’ in the formation of recombinant DNA. 

(b) Write the use of restriction endonuclease in the above process. 

Answer: (a) Palindromic nucleotide sequence is the recognition (specific) sequence present both on the vector and on a desired / alien DNA for the action of the same(specific) restriction endonuclease to act upon.

(b) Same restriction endonuclease binds to both the vector and the foreign DNA , cut each of the two strands of the double helix at specific points in their sugar phosphate backbone of recognition sequence for restriction endonucleases / palindromic sequence of vector and foreign DNA , to cut strand a little away from the centre of the palindrome sites, creates overhanging stretches /sticky ends . 

(b) If depict diagrammatically showing the above mentioned value points it can be accepted. 

 

Q.19. Describe the roles of heat, primers and the bacterium Thermus aquaticus in the process of PCR. 

Answer: Heat – Denaturation / separation of DNA into two strands.

Primer- Enzyme DNA Polymerase extend the primers using the nucleotides provided in the reaction and the genomic DNA as template. 

Thermus aquaticus – source of thermostable DNA polymerase / Taq polymerase. 

 

Q.20. Explain the various steps involved in the production of artificial insulin. 

Answer: Two DNA sequences corresponding to A and B polypeptide chains of human insulin were prepared , these were introduced into E.coli to produce A and B chains separately , these chains were extracted and combined by creating disulphide bonds.

 

Q.21. (a) “Organisms may be conformers or regulators.” Explain this statement and give one example of each. 

(b) Why are there more conformers than regulators in the animal world ? 

Answer: (a) Conformers- organisms which cannot maintain a constant internal environment under varying external environmental conditions / change body temperature and osmotic concentration with change in external environment eg. all plants / fishes / amphibians / reptiles.

Regulators – organisms which can maintain homeostasis (by physiological means or behavioural means ) // maintain constant body temperature and osmotic concentration eg. birds /mammals.

(b) Thermoregulation is energetically expensive for animals.

 

Q.22. Describe the inter-relationship between productivity, gross primary productivity and net productivity. 

Answer: Productivity is the rate of biomass production per unit area over a period of time , 

Gross primary productivity is the rate of production of organic matter during photosynthesis in an ecosystem , Net productivity is the gross primary productivity minus respiration losses ®.

 

Q.13. Explain the process of pollination in Vallisneria. How is it different in water-lily, which is also an aquatic plant ?

Answe: In Vallisneria pollination takes place through water , the female flower reach the surface of water by long stalk , male flowers / pollen grain released on to the surface of water , carried passively by water current reaching the female flowers / stigma.

In Water lily pollination takes place through wind or insect , female flower emerges above the surface of water and gets pollinated 

 

Q.15. What is disturbance in Hardy-Weinberg genetic equilibrium indicative of ? Explain how it is caused.

Answer: Disturbance in Hardy-Weinberg equilibrium is an indicator of change of frequency of alleles in a population , resulting in evolution.

It is caused by genetic drift / gene flow or gene migration / mutation / genetic recombination /natural selection. 

 

Q.18. Different animals respond to changes in their surroundings in different ways. Taking one example each, explain “some animals undergo aestivation while some others hiberna

tion”. How do fungi respond to adverse climatic conditions ?

Answer: Some animals go into aestivation to avoid summer related problems ( heat and desiccation) , eg. snails / fish ( any other suitable eg.) 

Some animals go into hibernation to avoid winter related problem ( extreme cold) eg. bear ( any other suitable eg.).

Fungi form thick walled spores and suspend their activities to respond to adverse climatic condition.

 

Q.11. Rearrange Ramapithecus, Australopithecus and Homo habilis in the order of thein evolution on the Earth. Comment on their evolutionary characteristics.

Answer: Ramapithecus Australopithecus Homo habilis.

Ramapithecus – hairy / walked like gorilla and chimpanzees / more man like.

Australopithecus – Hunted with stone weapons / ate fruit.

Homo habilis -Brain capacity 650- 800 cc / probably did not eat meat.

 

Q.16. (a) Trace the development of an endosperm after fertilisation with reference to coconut. Mention the importance of endosperm development.

(b) Write the importance of ‘pollen bank’.

Answer: (a) In coconut Primary Endosperm Nucleus (PEN-3n) undergoes successive nuclear divisions , give rise to free- nuclear endosperm known as coconut water , white kernel is the cellular endosperm , provides nourishment to the growing embryo.

(b) Storage / cryopreservation ( storage in liquid nitrogen at – 196 o C) , to use in crop breeding programmes.

 

Q.20. Describe the inter-relationship , between productivity, gross primary productivity and net productivity.

Answer: Productivity is the rate of biomass production per unit area over a period of time ,

Gross primary productivity is the rate of production of organic matter during photosynthesis in an ecosystem ,Net productivity is the gross primary productivity minus respiration losses ®.

 

Q.22. How do kangaroo rats and desert plants adapt themselves to survive in their extreme habitat ? Explain.

Answer:  Kangaroo rats- internal fat oxidation where water is a byproduct , excretes concentrated urine.

Desert Plants -thick cuticle / sunken stomata / leaves reduced to spines / deep roots /

Special photosynthetic pathway / CAM.

 

SECTION – D 

(Q No. 23 is of four mark) 

Q.23 . It is commonly observed that parents feel embarrassed to discuss freely with their adoles- cent children about sexuality and reproduction. The result of this parental inhibition is that the children go astray sometimes. 

(a) Explain the reasons that you feel are behind such embarrassment amongst some 

parents to freely discuss such issues with their growing children. 

(b) By taking one example of a local plant and animal, how would you help these parents 

to overcome such inhibitions about reproduction and sexuality ? 

Ans: (a) Illiteracy / conservative attitude / misconceptions / social myths / any other relevant point (Any two).

(b) If a student gives the clarity of the concept of reproduction and sexuality by taking any example of a plant and an animal with respect to reproductive organs, gamete formation, fertilization, sexual behaviour etc.

 

SECTION – E 

(Q Nos. 24-26 are of five marks each) 

Q.24. (a) When a seed of an orange is squeezed, many embryos, instead of one are observed. 

Explain how it is possible. 

(b) Are these embryos genetically similar or different ? Comment. 

Ans: (a) Polyembryony , nucellar cells surrounding embryo sac start dividing , protrude into the embryo 

sac and develop into many embryos. 

(b) These embryos are genetically similar, as produced from nucellar cells by mitotic division / formed without fertilisation (but different from the embryo formed by fertilization). 

OR 

Q.24. (a) Explain the following phases in the menstrual cycle of a human female: 

(i) Menstrual phase 

(ii) Follicular phase 

(iii) Luteal phase 

(b) A proper understanding of menstrual cycle can help immensely in family planning. 

Do you agree with the statement ? Provide reasons for your answer. 

Ans: (a) (i) Menstrual phase – first 3-5 days of the cycle where menstrual flow occurs due to break down of endometrial lining of the uterus, if the released ovum is not fertilised.

(ii) Follicular phase – from 5th to 14th day of the cycle where the primary follicles grow to become a fully mature Graafian follicle , endometrium of uterus regenerates , Graafian follicle ruptures to release ova (ovulation on 14th day). 

(iii) Luteal Phase – During 15th to 28th day remaining parts of graafian follicle transforms into the corpus luteum , secretion of progesterone (essential for maintenance of endometrium).

All these phases are under the influence of varying concentrations of pituitary and ovarian Hormone.

(b) Yes , can take appropriate precautions between 10th to 17th day of the menstrual cycle when the chances of fertilisation are high. 

 

Q.25. (a) Compare, giving reasons, the J-shaped and S-shaped models of population growth of a species.

               (b) Explain “fitness of a species” as mentioned by Darwin. 

Answer: 

J shaped – growth curve  S shaped- growth curve 
Resources are unlimited  Resources are limited 
Growth is exponential  Logistic Growth 
As resources are unlimited all individuals survive and reproduce  Fittest individual will survive and reproduce 
Growth Equation dN/dt=Rn (If explained) Growth Equation dN/dt=rN (k-N/K) (If explained)

Note – Marks to be awarded only if the corresponding difference is written. 

(b) When resources are limited , Competition occurs between individuals , the fittest will survive, 

who reproduce to leave more progeny. 

OR 

Q.25. (a) What is an ecological pyramid ? Compare the pyramids of energy, biomass and numbers. 

(b) Write any two limitations of ecological pyramids. 

Ans: (a) Graphical representation of the relationships among organisms at different trophic levels.

(b) It does not accommodate the food web / does not take into account the same species belonging to two or more trophic levels , Saprophytes are not given any place.

 

Q.26. (a) Describe the structure and function of a t-RNA molecule. Why is it referred to as an adapter molecule? 

(b) Explain the process of splicing of hn-RNA in a eukaryotic cell. 

Ans: (a) Clover-leaf shaped / inverted L shaped molecules has an anticodon loop with bases complementary to specific codon , has an amino acid acceptor end = 1+1 

As it reads the code on one hand and binds with the specific amino acid on the other hand.

(b) Introns are removed and exons are joined in a definite order. 

Process of splicing shown diagramatically. 

OR 

Q.26. Growth Equation dN/dt=rN (k-N/K) (If explained) Pyramid of Energy Pyramid of BioMass Pyramid of Numbers  Pyramid of Numbers Shows transfer of Energy from shows numbers of one trophic level to another 

organisms at each trophic level. Always upright Mostly upright but can be inverted Mostly upright can be 

inverted Shows transfer of amount of food/ biomass from one trophic level to another. Write the different components of a lac-operon in E.coli. Explain its expression while in an ‘open’ state. 

Ans: It consists of one regulatory gene(i) , promoter gene , operator gene , and three structural genes(z,y,a).

Lactose/ inducer binds to the repressor protein , makes it inactive so it cannot bind with operator, allows RNA Polymerase access to the promoter and transcription proceeds ,β -galactosidase , permease , transacetylase formed (by translation process for Lactose metabolism).

Q.25. (a) Explain Polygenic inheritance and Multiple allelism with the help of suitable examples.

(b) “Phenylketonuria is a good example that explains Pleiotropy.” Justify.

Answer: (a) Traits that are generally controlled by three or more genes , the phenotype reflects the contribution of each allele / effect of each allele is additive.

eg. Human skin colour , controlled by three genes (A , B, C).

In multiple allelism more than two alleles , govern the same character / phenotype.

eg . Human blood group (ABO system) , controlled by three different alleles (IA, IB, i). 

(b) In pleiotropy a single gene can exhibit multiple phenotypic expressions , in phenylketonuria single mutated gene express mental retardation and reduction in hair and skin pigmentation

OR

Q.25. (a) What is an operon ?

(b) Explain how a polycistronic structural gene is regulated by a common promoter and a

combination of regulatory genes in a lac-operon.

Answer: (a) An operon is a polycistronic structural gene which is regulated by a common promoter and regulator

gene / transcriptionally regulated system in which polycistronic structural gene is controlled by a common promoter and regulator gene.

(b) 

  • Lac operon consist of one regulatory gene i which codes for the repressor protein , promoter (P) and operator (o) are adjacent to gene i.
  • Structural genes z, y, a code for enzymes (â-galactosidase , permease and transacetylase respectively).
  • The regulator gene i synthesizes the repressor protein (all the time) , in the absence of inducer , the repressor protein binds to the operator region of the operon , prevents transcription (by RNA polymerase).
  • The repressor is inactivated in the presence of an inducer (lactose) that binds with it , this allows RNA polymerase access to promoter and transcription proceeds.

 

Q.24. (a) A pea plant bearing axial flowers is crossed with a pea plant bearing terminal flowers. The cross is carried out to find the genotype of the pea plant bearing axial flowers. Work out the cross to show the conclusions you arrive at.

(b) State the Mendel’s law of inheritance that is universally acceptable.

Answer: (i) If the plants is homozygous for the dominant trait

(ii) If the plants is heterozygous for the dominant trait A A a a (All plants with Axial Flower) A a a (50 % plants are with Axial ?ower and 50% plants with terminal ?ower) a

Conclusion : If all progeny show axial flowers ( dominant) the plant is homozygous (AA) ,

If 50 % of Progeny show Axial flower ( Dominant) and 50% Terminal flower ( Recessive) the plant is heterozygous.

(b) Law of Segregation , allelic pair segregate (separates) during gamete formation ( do not loose their identity ).

OR

Q.24. (a) Absence of lactose in the culture medium affects the expression of a Lac-operon in E. coli. Why and how ? Explain.

(b) Write any two ways in which the gene expression is regulated in eukaryotes.

Answer: (a) • Lactose acts as inducer thus absence of lactose switches off the operon.

• Repressor protein produced by regulatory gene ( i-gene ) is free ( in the absence of inducer ) ,

• Repressor protein binds with the operator gene ( o-gene ) ,

• Preventing RNA polymerase to transcribe the structural gene and operon is switched off.

If the above mentioned points are properly represented with help of schematic diagram.

(b) • Transcriptional level ( formation of primary transcripts )

• Processing level ( regulation of splicing )

• Transport of messengar RNA from nucleus to the cytoplasm

• Translational level 

 

Q.25. (a) When a seed of an orange is squeezed, many embryos, instead of one are observed. Explain how it is possible.

(b) Are these embryos genetically similar or different ? Comment.

Ans: (a) Polyembryony , nucellar cells surrounding embryosac start dividing , protrude into the embryosac and develop into many embryos = 1+ 1+ 1

(b) These embryos are genetically similar, as produced from nucellar cells by mitotic division / formed without fertilisation (but different from the embryo formed by fertilization)

OR

Q.25. (a) Explain the following phases in the menstrual cycle of” a human female:

(i) Menstrual phase

(ii) Follicular phase

(iii) Luteal phase

(b) A proper understanding of menstrual cycle can help immensely in family planning.

Do you agree with the statement ? Provide reasons for your answer.

Ans: (a) (i) Menstrual phase – first 3-5 days of the cycle where menstrual flow occurs due to break down of endometrial lining of uterus, if the released ovum is not fertilised.

(ii) Follicular phase – from 5th to 14th day of the cycle where the primary follicles grow to become a fully mature Graafian follicle , endometrium of uterus regenerates , Graafian follicle ruptures to release ova (ovulation on 14th day)

(iii) Luteal Phase – During 15th to 28th day remaining parts of graafian follicle transform into corpus luteum , secretion of progesterone (essential for maintenance of endometrium)

All these phases are under the influence of varying concentrations of pituitary and ovarian hormone.

(b) Yes , can take appropriate precautions between 10th to 17th day of the menstrual cycle when the chances of fertilisation are high.

Biology 12th Previous Year Question Paper 2018 (CBSE)

Biology

SECTION-A 

(Q. Nos. 1 – 5 are of one mark each) 

Q.1. Write the dual purpose served by Deoxyribonucleoside triphosphates in polymerisation. 

Ans. Acts as a substrate , provide energy (from the terminal two phosphates).

 

Q.2. Name two diseases whose spread can be controlled by the eradication of Aedes 

mosquitoes. 

Ans. Dengue , Chikungunya // Yellow Fever / Eastern Equine Encephalitis / West Nile Fever / Zika / Zika Virus Disease (Any two)..

 

Q.3. How do cytokine barriers provide innate immunity in humans ? 

Ans. Interferon (proteins) , secreted by virus infected cells (protect non – infected cells from further viral infection).

 

Q.4. Write the names of the following : 

(a) A 15 mya primate that was ape-like 

(b) A 2 mya primate that lived in East African grasslands 

Ans. (a) Dryopithecus. 

(b) Australopithecines / Australopithecus / Homo habilis. 

 

Q.5. Mention the chemical change that proinsulin undergoes, to be able to act as mature 

insulin. 

Ans. Removal of C – peptide (from proinsulin) 

 

SECTION-B 

(Q. Nos. 2 – 10 are of two marks each) 

Q.6. Your advice is sought to improve the nitrogen content of the soil to be used for the cultivation of a non-leguminous terrestrial crop. 

(a) Recommend two microbes that can enrich the soil with nitrogen. 

(b) Why do leguminous crops not require such enrichment of the soil ? 

Ans. (a) Azospirillum / Azotobacter / Anabaena / Nostoc / Oscillatoria / Frankia (Any 

two correct names of microbes)..

(If cyanobacteria mentioned. , but if along with cyanobacteria Anabaena / Nostoc / Oscillatoria mentioned then No mark on cyanobacteria) 

(b) They can fix atmospheric nitrogen , due to the presence of Rhizobium / N2 fixing bacteria 

in their root nodules..

 

Q.7. With the help of an algebraic equation, how did Hardy-Weinberg explain that in a given population the frequency of occurrence of alleles of a gene is supposed to remain the same through generations ? 

Ans. In a population of diploid organisms 

If the frequency of allele A = p and frequency of allele a = q. 

Expected genotype frequency under random mating are 

AA = p2 (for the AA homozygotes)

aa = q2 (for the aa homozygotes) 

Aa = 2pq (for the Aa heterozygotes). 

(In absence of selection , mutation , genetic drift or other forces allelic frequency p and q are constant through generations) 

Therefore p2 + 2pq +q2 = 1 = 1 

OR 

Q.7. Although a prokaryotic cell has no defined nucleus , yet DNA is not scattered throughout the cell. Explain. 

Ans. DNA is negatively charged , positively charged proteins , hold it in places , in large loops (in a region termed as nucleoid). × 4 

 

Q.8. How did a citizen group called Friends of the Arcata Marsh, Arcata, California, USA, help to improve water quality of the marshland using Integrated Waste Water Treatment ? Explain in four steps. 

Ans.- Water is treated by conventional method / sedimentation / filtration / chlorination 

– Water flows to six connected marshes 

– The water in marshes is seeded with appropriate plants / algae / fungi / 

bacteria 

– Which helps to neutralise the pollutants / assimilate the pollutants / absorb pollutants / Remove heavy metals. × 4 

 

Q.9. You have obtained a high yielding variety of tomatoes. Name and explain the procedure that ensures retention of the desired characteristics repeatedly in large populations of future generations of the tomato crop. 

Ans. – Tissue culture / micropropagation / somaclonal propagation / apomixis. 

– Explant / any part of plant taken out and grown (in a test tube / vessel) , 

– under sterile conditions , 

– in special nutrient medium (containing carbon source / sucrose , inorganic salt 

vitamins / amino acids and growth regulator). × 3 

 

Q.10. (a) Name the source plant of heroin drug. How is it obtained from the plant ? 

(b) Write the effects of heroin on the human body. 

Ans. (a) – Papaver somniferum / Poppy plant. 

– Extracted from latex of the plant / acetylation of morphine (obtained from the 

latex of plant). 

(b) Depressant , slows down body function..

 

SECTION-C 

(Q. Nos. 11 – 22 are of three marks each) 

Q.11. Draw a diagram of a mature human sperm. Label any three parts and write their 

functions. 

(Any three labelling).

Plasma membrane – Envelope of the sperm 

Acrosome – Filled with enzyme that help fertilization of ovum 

Mitochondria – Energy source for swimming 

Middle Piece – Possess mitochondria which is the energy source for swimming 

Tail – For movement of sperm 

Nucleus – Containing chromosomal material 

(Functions of the parts labelled ). × 3 

 

Q.12. (a) Expand VNTR and describe its role in DNA fingerprinting. 

(b) List any two applications of DNA fingerprinting technique. 

Ans. (a) VNTR – Variable Number of Tandem Repeat(s). 

– used as a probe (because of its high degree of polymorphism). 

(b) Forensic science / criminal investigation (any point related to forensic science) / determine population and genetic diversities / paternity testing / maternity testing / study of evolutionary biology (Any two).

 

Q.13. Differentiate between Parthenocarpy and Parthenogenesis. Give one example of each. 

Ans. 

Parthenocarpy Parthenogenesis 
– Formation of fruit without fertilization  – New organism develops without fertilization 
– e.g. banana / grapes / any other correct example. – e.g. Drones /male honey bee / turkey / rotifers / some lizards / any other correct example. 

 

Q.14. Medically it is advised to all young mothers that breastfeeding is the best for their 

newborn babies. Do you agree ? Give reasons in support of your answer. 

Ans.Yes, 

provides nutrition (calcium , fats , lactose ) / provides (passive) immunity / provides antibodies / Ig A. 

 

Q.15. Explain the mechanism of ‘sex determination’ in birds. How does it differ from that of 

human beings ? 

Ans. In birds ; 

Birds : female heterogamety / female produces (Z) type and (W) type of gametes. 

Humans : male heterogamety / male produces (X) and (Y) type of gametes. 

 

Q.16. (a) How has the development of bioreactor helped in biotechnology ? 

(b) Name the most commonly used bioreactor and describe its working. 

Ans. (a) Larger biomass / large volume of culture can be processed leading to higher yields of desired specific products (protein / enzymes) , under controlled conditions..

(b) Stirring type. 

– Mixing of reactor contents evenly (with agitator system or a stirrer). 

– Facilitates oxygen availability. 

– Temperature / pH / foam control // under optimum conditions. 

 

Q.17. Explain the roles of the following with the help of an example each in recombinant 

DNA technology: 

(a) Restriction Enzymes 

(b) Plasmids 

Ans. (a) It recognises a specific sequence of base pairs / palindromes, and cuts the DNA 

strand at a specific site..

eg. EcoRI / Hindiii or any other correct example. 

(b) Act as vectors / cloning of desired alien gene / foreign gene = 1 

eg. pBR322 / plasmid of Salmonella / plasmid of Agrobacterium / Ti Plasmid / Tumour inducing Plasmid. 

 

Q.18. Explain out-breeding, out-crossing and crossbreeding practices in animal husbandry. 

Out breeding – Breeding of unrelated animals (which may be between individual of 

same breed or between individuals of different species) = 1 

Outcrossing – (a kind of out breeding) Mating of animals within the same breed but having no common ancestors on either side of their pedigree upto 4 – 6 generations = 1 

Cross breeding – (another type of out breeding) Superior males of one breed are mated 

with superior females of another breed = 1 

 

Q.19. (a) Organic farmers prefer biological control of diseases and pests to the use of 

chemicals for the same purpose. Justify. 

(b) Give an example of a bacterium, a fungus and an insect that are used as 

biocontrol agents. 

Ans. (a) – Reduces dependence on toxic chemicals 

– Protects our ecosystem or environment 

– Protects and conserves non-target organisms / they are species – specific 

– These chemicals being non-biodegradable may pollute the environment 

permanently 

– These chemicals being non-biodegradable may cause biomagnification 

(b) Bacteria – Bacillus thuringiensis. 

Fungus – Trichoderma. 

Insect – Ladybird / Dragonfly / Moth or any other correct example. 

 

Q.20. (a) Differentiate between analogous and homologous structures. 

(b) Select and write analogous structures from the list given below : 

(i) Wings of butterflies and birds 

(ii) Vertebrate hearts 

(iii) Tendrils of bougainvillea and cucurbita 

(iv) Tubers of sweet potato and potato 

Ans. (a) Analogous – Anatomically not similar though perform similar functions / are a 

result of convergent evolution = 1 

Homologous – Anatomically similar (but perform different functions) / are a result 

of divergent evolution = 1 

(b) Option (i) Wings of butterflies and birds / (iv) Tubers of sweet potato and potato 

 

Q.21. (a) “India has greater ecosystem diversity than Norway.” Do you agree with the 

statement ? Give reasons in support of your answer. 

(b) Write the difference between genetic biodiversity and species biodiversity 

that exists at all levels of biological organisation. 

Ans. (a) Yes. 

India / tropical region Norway / temperate region 

– are less seasonal – more seasonal / 

/ more constant / more predictable / less constant / less predictable 

– promote niche specialisation – do not promote niche specialisation 

leading to greater biodiversity leading to low biodiversity 

– Species diversity increases as we – Species diversity decreases as we 

move towards equator move away from equator 

– More number of species exist – Less number of species exist 

(b) Genetic diversity – Diversity / variation within a species over its distributional range / same explained with the help of a correct example = 1 

Species diversity – Diversity / variation at a species level / same explained with 

the help of a correct example = 1 

OR 

Q.21. Explain the effect on the characteristics of a river when urban sewage is discharged into it. 

Ans. – Rise in organic matter , leads to increased microbial activity / growth of microbes.

– It results in a decrease in dissolved oxygen / rise in BOD / rise in Biochemical Oxygen 

Demand = 1 

– Leads to fish mortality / algal bloom / colour change / foul odour / increase in 

toxicity.

 

Q.22. How has the use of Agrobacterium as vectors helped in controlling Meloidogyne 

incognitia infestation in tobacco plants ? Explain in correct sequence. 

Ans. – Using Agrobacterium vector nematode specific genes introduced into host plant 

– Sense and antisense strands of mRNA are produced 

– ds RNA is formed 

– ds RNA initiates RNAi 

– Prevents translation of mRNA / silencing of mRNA of parasite / nematode 

– Parasite will not survive 

 

SECTION-D 

(Q. Nos. 23 is of four marks) 

Q.23. Looking at the deteriorating air quality because of air pollution in many cities of the country, the citizens are very much worried and concerned about their health. The doctors have declared health emergency in the cities where the air quality is very severely poor. 

(a) Mention any two major causes of air pollution. 

(b) Write any two harmful effects of air pollution to plants and humans. 

(c) As a captain of your school Eco-club, suggest any two programmes you would plan to organise in the school so as to bring awareness among the students on how to check air pollution in and around the school. 

Ans. (a) Vehicular discharge / smoke from industries / burning of agricultural wastes / smoke from incinerator / dust / smoke from thermal plants or any other correct cause 

(b) Reduces growth of plants / reduces yields of crops / premature death of plants / respiratory problems / acid rain / any other relevant point (Any two – one from plant and one from human)

(c) Plantation drive / awareness programmes through posters / nukkad natak / film show 

/ rallies / debates or any other 

 

SECTION-E 

(Q. Nos. 24 – 26 are of five marks each) 

Q.24. (a) Describe any two devices in a flowering plant which prevent both autogamy and 

geitonogamy. 

(b) Explain the events upto double fertilisation after the pollen tube enters one of 

the synergids in an ovule of an angiosperm. 

Ans. (a) – Dioecy / production of unisexual flowers (in different plants) 

– Self incompatibility. 

(b) – Pollen tube releases 2 male gametes in the cytoplasm of synergid 

– One male gamete fuses with egg cell / syngamy , resulting in diploid zygote 

– Other male gamete fuses with polar nuclei / triple fusion , to form triploid PEN (Primary Endosperm Nucleus) / PEC (Primary Endosperm Cell). 

OR 

Q.24. (a) Explain menstrual cycle in human females. 

(b) How can the scientific understanding of the menstrual cycle of human females 

help as a contraceptive measure ? 

Ans. (a) – Menstrual Phase – Menstrual flow occurs / due to breakdown of endometrial 

lining of uterus , when fertilization does not occur 

– Follicular Phase – Primary follicles grow into mature graafian follicles and endometrium regenerates through proliferation , changes induced by pituitary and ovarian hormones 

– Ovulatory Phase – LH surge , induces rupture of graafian follicle and release 

of secondary oocyte / ovum during middle of cycle (i.e. 14th day) 

– Luteal phase – Ruptured graafian follicle transforms into the corpus luteum which secrete large amounts of progesterone , essential for maintaining endometrium.

(b) Because ovulation occurs during mid cycle chances of fertilisation are very high 

so , couples should abstain from coitus between day 10 – 17.

 

Q.25. (a) Write the scientific name of the organism Thomas Hunt Morgan and his colleagues worked with for their experiments. Explain the correlation between linkage and recombination with respect to genes as studied by them. 

(b) How did Sturtevant explain gene mapping while working with Morgan ? 

Ans. (a) Drosophila melanogaster. 

They observed that two genes (located closely on a chromosome) did not segregate independently of each other (F2 ratio deviated significantly from 9 : 3 : 3 : 1). 

Tightly linked genes tend to show fewer (less) recombinant frequency of parental traits / show higher (more) frequency of parental type. 

Loosely linked genes show higher percentage (more) of recombinant frequency of parental traits / lower frequency percentage of parental type. 

Genes present on the same chromosome are said to be linked and the recombinant frequency depends on their relative distance on the chromosome. 

(b) He used the frequency of recombination between gene pairs on the same chromosome , as a measure of the distance between genes and mapped their position on the chromosome 

OR 

 

Q.25. (a) State the ‘Central dogma’ as proposed by Francis Crick. Are there any 

exceptions to it ? Support your answer with a reason and an example. 

(b) Explain how the biochemical characterisation (nature) of ‘Transforming Principle’ was determined, which was not defined from Griffith’s experiments. 

Ans. (a)

Yes, in some viruses flow of information is in reverse direction/reverse transcription.

(b) Protein and DNA and RNA were purified from heat killed S strain / smooth 

Streptococcus / Diplococcus pneumoniae. 

Protein + Protease → transformation occurred (R cell to S type). 

RNA + RNA base → transformation occurred (R cell to S type). 

DNA + DNAse → transformation inhibited. 

Hence DNA alone is the transforming material. 

 

Q.26. (a) Following are the responses of different animals to various abiotic factors. 

Describe each one with the help of an example. 

(i) Regulate 

(ii) Conform 

(iii) Migrate 

(iv) Suspend 

(b) If 8 individuals in a population of 80 butterflies die in a week, calculate the death rate of population of butterflies during that period. 

Ans.

(a) (i) Regulate – Maintain constant internal temperature / osmotic concentration /homeostasis. e.g. birds / mammals. 
(ii) Conform – Do not maintain constant internal temperature / osmotic concentration / No homeostasis. e.g. any one example of animals other than birds and mammals. 
(iii) Migrate – Temporary movement of organisms from the stressful of habitats to hospitable areas and return when stressful period is over. e.g. birds from Siberia / or any other correct example. 
(iv) Suspend – Reducing / minimising the metabolic activities during unfavourable conditions. e.g. Polar bear / amphibian / snails / fish / any other examples of animals. 

(b) Death rate = 8/80 = 0.1, individuals per butterfly per week.

OR 

 

Q.26. (a) What is a trophic level in an ecosystem ? What is ‘standing crop’ with reference to it ? 

(b) Explain the role of the ‘first trophic level’ in an ecosystem. 

(c) How is the detritus food chain connected with the grazing food chain in a 

natural ecosystem ? 

Ans. (a) Specific place of an organism in a food chain , mass of living material (biomass) at each trophic level at a particular time.

(b) First trophic level has producers / autotrophs , which trap solar energy / to produce 

food (photosynthesis). 

(c) Organisms of the Detritus food chain (DFC) are the prey to the Grazing food chain (GFC) organism , the dead remains of GFC are decomposed into simple inorganic materials which are absorbed by DFC organisms. 

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