CBSE Class 12 Biology Sample Paper Set-7


CBSE Class 12 Biology
Sample Paper
Set-7


CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7

Section A

1.What do you mean by the terms staminate and pistillate flowers? Discuss each with examples.

2.What are exotic species?

3.State the category of viruses that carries the process of reverse transcriptase. What is the purpose of this enzyme?

4.It is often said that noise level can be reduced by placing the carpets and drapes on the floor or wall surfaces in a room. If it is true, give reason.

5.How does silencing of specific mRNA in RNA interference prevent parasitic infestation?

Section B

6.Do you think that the zygote becomes dormant for sometimes in a fertilised ovule? Justify.

7.A female player in your locality has been banned from playing because of the absence of one X-chromosome (i.e. 45 with XO). Mention the name of such syndrome along with other symptoms. Does this behaviour is really applicable?

8.Draw the sketch of a zoospore and a conidium.
Or
Mention one dissimilarity between them and two feature common to both structure.

9.A environmentalist believes that if the level of dissolved oxygen of water gets dropped to zero, the water will become septic in nature. Explain giving an example of an aquatic body.

10.How do kangaroo rats live in the absence of water in North American deserts?

Section C

11.What are the advantages of using biofertilisers in agriculture?

12.A policeman finds a very small piece of body tissue from the site of a crime and takes it to the forensic department.
(i)By which technique will they amplify the DNA collected from the tissue sample?
(ii)Mention in a sequence, the three steps involved in each cycle of this technique.
(iii)What is the role of thermostable DNA polymerase in this technique?

13.Illustrate the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR) diagrammatically.

14.What are CFCs? Explain their contribution in ozone depletion. List out the harmful effects of ozone depletion.

15.Work out a flowchart representation of a process of fertilisation in human body initiating from the discharge of semen into female’s vagina till the fusion with ovum to form a diploid zygote.

16.A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

17.A fRNA is charged with amino acid methionine.
(i)Name the process involved in the attachment.
(ii)Point out the mRNA codon and anticodon fRNA for this amino acid.
(iii)What is heterochromatin?

18.A biotechnologist while growing a recombinant bacterium in a bioreactor forgets to add an antibiotic to the medium. What is the logic behind using antibiotic in such medium? Does its adding or not adding really makes an issue? Justify.

19.Sachin when visited doctor, he confirmed that Sachin is being suffering from a chicken fox. His father got stressed. Doctor said that there is nothing to get worried about because he will not have the same disease for rest of his life. Explain the reason behind doctor’s such saying.

20.Draw a labelled diagram of seminiferous tubule.

21.In what way the plants gets benefitted from the mycorrhizal symbiotic association? Give any three benefits.

22.What are STDs? What are the other terms used for STDs?

Section D

23.Ankita had a fight with her friend while discussing about the process of evolution. As she told her friend that evolutionary process is continuous and everything around the globe is evolving. Her friend rather argues and said that ‘we humans are not evolving’. Whom do you think is correct Ankita, her friend or both of them? Write your views about this fact.

Section E

24.(i) Explain the following terms.
(a)Food web (b) Trophic level
(ii)Give diagrammatic representation of trophic levels in the ecosystem with the appropriate diagrams.
Or
(i)(a) Name the biogeochemical (nutrient) cycle shown below.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
(b)Name an activity of the living organisms not depicted in the cycle by which this nutrient is returned to the atmosphere.
(ii)How would the flow of nutrient in the cycle be affected due to large scale deforestation? Explain giving reasons.
(iii)Describe the effect of an increased level of this nutrient in the atmosphere on our environment.

25.(i) Discuss and workout Mendel’s monohybrid cross upto F2 generation expressing an example of seed coat colour as a trait in Pisum sativum.
(ii)State the law of inheritance been derived from such a cross.
(iii)How is the phenotypic ratio of F2 -generation different in a dihybrid cross?
Or
(i)You are given tall pea plants with yellow seeds, whose genotypes are unknown. How would you find the genotype of these plants? Explain with the help of cross.
(ii)Identify A, B and C in the table given below.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7

26.Write a detailed note on preventive measures for various diseases and their importance.
Or
(i)How normal cells get transformed into cancerous neoplastic cells? Mention the difference between viral oncogenes and cellular oncogens.
(ii)Write a short note on detection of cancer.

Answers

Section A

1.What do you mean by the terms staminate and pistillate flowers? Discuss each with examples.
Ans.Staminate flowers are those which lacks pistils g., Cucurbits while Pistillate flowers are the one that lacks stamens, e.g., Papaya.

2.What are exotic species?
Ans.Exotic species also termed as alien species are those species that are not naturally found in the habitat. They are mostly introduced in a habitat from outside. They can become invasive too.

3.State the category of viruses that carries the process of reverse transcriptase. What is the purpose of this enzyme?
Ans.Viruses carrying reverse transcriptase are retroviruses which have RNA as their genetic material. These viruses catalyses formation of DNA from RNA.

4.It is often said that noise level can be reduced by placing the carpets and drapes on the floor or wall surfaces in a room. If it is true, give reason.
Ans.Yes, it is true because these materials act as sound absorbing material and therefore, can reduces the effect of both high and low pitched sounds. For greater effectiveness, these materials should even be installed as much close to the noise source as possible.

5.How does silencing of specific mRNA in RNA interference prevent parasitic infestation?
Ans.Parasitic infestation can be prevented by using RNA interference (RNAi) process, which is checked by silencing of specific mRNA due to a complementary c/sRNA which binds and prevents translation of the mRNA (silencing).

Section B

6.Do you think that the zygote becomes dormant for sometimes in a fertilised ovule? Justify.
Ans.Zygote is dormant for sometime in a fertilised ovule because it develops only after the development of an endosperm.This is an adaptation to ensure nutrition to the growing embryo.

7.A female player in your locality has been banned from playing because of the absence of one X-chromosome (i.e. 45 with XO). Mention the name of such syndrome along with other symptoms. Does this behaviour is really applicable?
Ans.The player has Turner’s syndrome in which the females are sterile in character because their ovaries behaves as rudimentary. They also lack other secondary sexual characters. Avoiding such person and isolating her from the locality because of this chromosomal syndrome is not applicable because chromosomal disorders are not communicable in nature.

8.Draw the sketch of a zoospore and a conidium.
Or
Mention one dissimilarity between them and two feature common to both structure.
Ans.The sketch of a typical zoospore and conidium are given below
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
Or
Similarity
(i)Both zoospore and conidium are the asexual reproductive structures.
(ii)Both (zoospore) Chlamydomonas and (conidia)Penicillium belong to kingdom-Fungi.
Dissimilarity
Zoospores are motile asexual reproductive structure, whereas, conidia are non-motile asexual reproductive structure.

9.A environmentalist believes that if the level of dissolved oxygen of water gets dropped to zero, the water will become septic in nature. Explain giving an example of an aquatic body.
Ans.Level of dissolved oxygen acts as an important measure of the health of any stream, because this oxygen which dissolves in water through the mixing of water surface with the atmosphere is been used by the fishes and another aquatic bodies and plants. If the levels fall too low, these organisms and plants fails to survive as the water becomes septic and smells rotten due to the dominancy or high growth of a low oxygen sulphur bacteria in it.

10.How do kangaroo rats live in the absence of water in North American deserts?
Ans.Kangaroo rats are capable to live in the absence of water through their internal fat oxidation in which water acts a by product. They also has the ability to concentrate their urine to a minimal volume.

Section C

11.What are the advantages of using biofertilisers in agriculture?
Ans.Following are the advantages of using bioferti/isers in agriculture
(i)Biofertilisers does not cause any pollution.
(ii)These are cheap and economical.
(iii)Some of them also act as biopesticides.
(iv)In ill-irrigated conditions, few biofertilisers can enhance the crop yield.
(v)They improve soil structure and functions.
(vi)They make vitamins and other growth promoting biochemicals available

12.A policeman finds a very small piece of body tissue from the site of a crime and takes it to the forensic department.
(i)By which technique will they amplify the DNA collected from the tissue sample?
(ii)Mention in a sequence, the three steps involved in each cycle of this technique.
(iii)What is the role of thermostable DNA polymerase in this technique?
Ans.(i) DNA fingerprinting is a very useful technique to identify criminals in the forensic laboratories.
(ii)Three steps involved in the process of DNA fingerprinting are
Step I In which, DNA is cut into fragments with restriction enzymes into precise reproducible sequence.
Step II In which, the separated DNA sequence are transformed on to a nitrocellulose or nylon membrane.
Step III In which, the sequence probes target a specific nucleotide sequence that is complementary to them.
(iii)Thermostable DNA polymerase [taq DNA Polymerase) is used to catalyse the reaction in order to produce many copies of the extracted DNA by the use of PCR.

13.Illustrate the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR) diagrammatically.
Ans.Polymerase Chain Reaction (PCR)
PCR is a reaction in which amplification of specific DNA sequences is carried out in vitro.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7

14.What are CFCs? Explain their contribution in ozone depletion. List out the harmful effects of ozone depletion.
Ans.CFCs are chlorofluorocarbons widely used as refrigerants. CFCs being discharged in the lower part of atmosphere move upward and reaches the stratospheric layer of the atmosphere. UV rays act on CFCs and releases Cl atoms which in turn degrades ozone releasing molecular oxygen and affects ozone levels.
Harmful Effects of Ozone Depletion
(i)UV-B damage DNA and may cause mutation.
(ii)Causes ageing of skin, damage to skin cells and various types of skin cancers.
(iii)In human eyes, cornea absorbs UV-B radiation and a high dose of UV-B causes inflammation of cornea called snow blindness, cataract, etc.

15.Work out a flowchart representation of a process of fertilisation in human body initiating from the discharge of semen into female’s vagina till the fusion with ovum to form a diploid zygote.
Ans.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7

16.A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?
Ans.DNA bands may not be observed when a mixture of fragmented DNA was electrophoresed, due to following reasons
(i)Concentration of agarose in the gel is not proper, as greater, the concentration of agarose gel used, greater will be the facilitation of the separation of small DNA fragments. Whereas, smaller the concentration of agarose, higher will be the resolution of bands.
(ii)If the concentration of salt in the buffer is not proper.
(iii)If the DNA sample is contaminated with RNA or any other impurity or if the concentration of DNA is too low.

17.A fRNA is charged with amino acid methionine.
(i)Name the process involved in the attachment.
(ii)Point out the mRNA codon and anticodon fRNA for this amino acid.
(iii)What is heterochromatin?
Ans.(i) Translation
(ii)mRNA codon is AUG and anticodon on fRNA is UAC.
(iii)Chromatin that is more densely packed, stains dark and is called heterochromatin.

18.A biotechnologist while growing a recombinant bacterium in a bioreactor forgets to add an antibiotic to the medium. What is the logic behind using antibiotic in such medium? Does its adding or not adding really makes an issue? Justify.
Ans.Yes, forgetting to add antibiotic in a medium will really harm. Because antibiotic in any medium growing recombinant bacterium acts as tool because in the absence of an antibiotic, there will be no pressure on recombinants to retain the plasmid which is eventually carrying the gene of our interest. And the high copy number of plasmid which acts as a metabolic burden will fail to get maintained.

19.Sachin when visited doctor, he confirmed that Sachin is being suffering from a chicken fox. His father got stressed. Doctor said that there is nothing to get worried about because he will not have the same disease for rest of his life. Explain the reason behind doctor’s such saying.
Ans.When the boy suffered first time from chickenpox, his body’s immune system exhibited primary response. Along with that, the memory of chickenpox virus was stored by the immune system. Now, whenever the same virus will attack this boy, the immune system will produce an intense response, preventing the body from getting chickenpox again. Thus, protecting the boy from getting infected by chickenpox forever in life.

20.Draw a labelled diagram of seminiferous tubule.
Ans.Diagrammatic sectional view of a seminiferous tubule is given below
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7

21.In what way the plants gets benefitted from the mycorrhizal symbiotic association? Give any three benefits.
Ans.Plants may be benefitted by the mycorrhizal association in the following ways
(i)Plants may become resistant to root borne pathogens
(ii)They even become tolerant to salinity and drought
(iii)Growth and development of the plant get increased.

22.What are STDs? What are the other terms used for STDs?
Ans.Sexually Transmitted Diseases (STDs) are the diseases that are mainly passed one from one person to another during the sexual contact. They are also known as veneral diseases or reproductive tract infections. The common way to prevent the transmission of STDs is to avoid unprotected sexual contact. However, some STDs like genital herpes can still be passed even if a condom is used. Early medication with the help of a doctor can give some relief.

Section D

23.Ankita had a fight with her friend while discussing about the process of evolution. As she told her friend that evolutionary process is continuous and everything around the globe is evolving. Her friend rather argues and said that ‘we humans are not evolving’. Whom do you think is correct Ankita, her friend or both of them? Write your views about this fact.
Ans.Human evolution means the evolutionary process that leads to the appearance of anatomically modern humans. When we think of human evolution our minds wonder back to the thousands of years it took natural selection to produce the man modern day by day. But the question arises that are we still changing or evolving is a species, even today also.
So, it has been scientifically proved that despite modern technology and industrialisation, human continued to evolve. Also it is not only that we are evolving, were doing so even faster than before. In last 10,000 years, the pace of our evolution has been speed up to 100 times, creating more mutation. For example, human are losing their wisdom teeth, become more resisting to various diseases and brains have shrinked than before, etc.

Section E

24.(i) Explain the following terms.
(a)Food web (b) Trophic level
(ii)Give diagrammatic representation of trophic levels in the ecosystem with the appropriate diagrams.
Or
(i)(a) Name the biogeochemical (nutrient) cycle shown below.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
(b)Name an activity of the living organisms not depicted in the cycle by which this nutrient is returned to the atmosphere.
(ii)How would the flow of nutrient in the cycle be affected due to large scale deforestation? Explain giving reasons.
(iii)Describe the effect of an increased level of this nutrient in the atmosphere on our environment.
Ans.(i) (a) Food Webs All organisms depend upon one or other for food and hence, forms food chain, these naturally occurring food chains makes further the food webs.
(b) Trophic Level is a specific position of an organism based on the source of nutrition in the food chain. All organisms occupy a particular place in their natural surrounding or in a community according to their feeding relationship with other organisms.
(ii) Representation of trophic levels in the ecosystem is given below
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
Or
(i)(a) The given biogeochemical cycle shown is a carbon cycle.
(b) Volcanic activity and mining or microbial decomposition of organic matter.
(ii)Due to large scale deforestation, the flow of carbon in the environment will be disturbed because plants are the major consumers, which utilise carbon in photosynthesis. This would lead to accumulation of carbon in the atmosphere.
(iii)Increase in the level of carbon in atmosphere will result in greenhouse effect. This will lead to heating of earth’s surface and finally to global.

25.(i) Discuss and workout Mendel’s monohybrid cross upto F2 generation expressing an example of seed coat colour as a trait in Pisum sativum.
(ii)State the law of inheritance been derived from such a cross.
(iii)How is the phenotypic ratio of F2 -generation different in a dihybrid cross?
Or
(i)You are given tall pea plants with yellow seeds, whose genotypes are unknown. How would you find the genotype of these plants? Explain with the help of cross.
(ii)Identify A, B and C in the table given below.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
Ans.(i) In monohybrid cross, when homozygous dominant and homozygous recessive parents are crossed, F-, hybrid would be heterozygous for that trait and would express as the dominant allele.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
(ii)The hybrid is heterozygous containing both alternative alleles (e., Y and y) but only one trait, i.e., yellow colour appeared and green colour trait is suppressed in generation. This shows that yellow seed colour is dominant over the green seed colour trait. This explains Mendel’s law of dominance.
(iii)Phenotypic ratio in F2-generation: In monohybrid cross 3 : 1
In dihybrid cross -9 : 3 : 3 : 1
Or
(i) The given tall pea plant with yellow seeds need to be crossed with a dwarf plant with green seeds. The dominant traits are tallness and yellow colour of seeds. The recessive traits are dwarfness and green colour of seeds.Cross between tall plant/yellow seeds and dwarf plant/green seeds.
CBSE Sample Papers for Class 12 Biology Solved 2016 Set 7
In this cross, the Frgeneration shows four phenotypes in the ratio of 1 : 1 : 1 : 1. So, the given plant is heterozygous for both the traits.
(ii) A – Dominant trait, B- Dominance
C – Phenotype obtained in blending of two parental trait

26.Write a detailed note on preventive measures for various diseases and their importance.
Or
(i)How normal cells get transformed into cancerous neoplastic cells? Mention the difference between viral oncogenes and cellular oncogens.
(ii)Write a short note on detection of cancer.
Ans.Different diseases have a specific set of preventive measures
(i)Preventive measures for diseases spread by contaminated food and water
(a)Measures for personal hygiene

  • Keeping body clean, cutting nails and hair regularly.
  • Consumption of clean water and contamination free food, vegetables and fruits.
  • Washing hands before every meal and after defection.
  • Cooking the food in clear water and keeping it at safe temperature.
  • Storing raw and cooked food separately.

(b)Measure for public hygiene

  • Proper disposal of waste and excreta.
  • Cleaning and disinfection of pools, water tanks and other water reservoirs.
  • Hygienic practice should be adopted at restaurants and hotels.

(ii)Preventive measures for air borne disease
(a)Close contact with infected person should be avoided.
(b)Use of same towels and other articles of infected person should be avoided.
(c)Washing hands regularly after sneezing, coughing, etc.
(iii)Preventive measures for vector borne disease

  • Breeding places of vector should be eliminated.
  • Stagnation of water should be avoided to control the breeding of mosquitoes.
  • Use of mosquito repellents, nets and wire mesh on doors and windows.
  • Wearing protective clothes like pants and full sleeves shirt, etc.

Or
(i)The uncontrolled proliferation of cells results in clones called neoplasm or tumour. In this way a normal cell get transformed into a cancerous cell.
Viral Oncogenes These are the viral genes, which cause cancer.
Cellular Oncogenes These are the genes in normal cells, which cause a cell to become cancerous under certain conditions.
(ii)Cancer detection is considered to be the first step towards treatment. Its early detection is essential for its cure.
Some of the ways to detect cancer are
(i)Biopsy A piece of the suspected tissue cut into thin sections is stained and examined under microscope.
(ii)Computed Tomography It uses X-ray to generate a three-dimensional image of the object.
(iii)MRI It uses strong magnetic fields and non-ionising radiations to accurately detect pathological changes in the living tissue.
(iv)Antibodies against cancer-specific antigens are also used for the detection of certain cancers.

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