CBSE Sample Papers for Class 12 Biology – CBSE Biology Questions and Answers
CBSE Biology Sample Paper
1. What is a cistron?
Cistron is that segment of DNA which specifies synthesis of a polypeptide.
2. Why do children cured by enzyme-replacement therapy for adenosine deaminase deficiency need periodic treatment?
The introduction of genetically engineered lymphocytes into an ADA deficiency patient is not a permanent cure because, the genetically engineered lymphocytes die after some days. Hence, the patient requires periodic infusion of genetically engineered lymphocytes, so the cure is not permanent.
3. List two advantages of the use of unleaded petrol in automobiles as fuel.
Following are the two advantages of using unleaded petrol as fuel in automobiles: The use of unleaded petrol in vehicles fitted with catalytic converters help in reducing emission of poisonous gases. As unleaded petrol does not emit harmful compounds, it helps in preventing health diseases like bronchitis, asthma and lung diseases.
4. Why do moss plants produce very large number of male gametes? Provide one reason. What are these gametes called?
Mosses are bryophytes and they need water for fertilisation. They lay their flagellated male gametes that swim across the water to reach the female gamete. During this process, many of the male gametes are destroyed or lost. Thus, moss plants produce very large number of male gametes so that even if some of the gametes get destroyed, the remaining can fertilise the female gamete. These male gametes are called antherozoids.
5. (a) Why are the plants raised through micropropagation termed as somaclones? (b) Mention two advantages of this technique.
(a) The plants obtained by micropropagation are called somaclones because they are genetically identical plants developed from any part of a plant by tissue culture.
(b) The advantages of micropropagation are as follows:
(i) It helps in the propagation of a large number of plants in a short span of time.
(ii) Healthy plant can be recovered from diseased plant by meristem culture because meristem are free of viruses in diseased plant.
6. Explain the different steps involved during primary treatment phase of sewage.
(a) It is a physical process of removal of small and large particles through filtration and sedimentation.
(b) The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequential smaller pore sizes.
(c) Sewage is then passed into the grit chamber, where grit is sedimented.
(d) Sewage is then allowed to pass into the settling tank, where the suspended materials settle down to form primary sludge.
(e) Effluent is then taken for the secondary treatment.
7. State what is apomixis. Comment on its significance. How can it be commercially used?
Apomixis: It is a form of asexual reproduction that mimics sexual reproduction, and seeds are produced without fertilisation. It is called apomixis or agamospermy, e.g., Grasses.
Signifiance: Diploid egg cell is formed without reduction division and develops into embryo without fertilisation eg. Asteraceae and Grasses. Commercial applications of apomixis:
(i). By apomixis, hybrid varieties of seeds can be produced, which will provide higher and better yield.
(ii). Apomixis prevents the loss of specific characteristics in the hybrid plants.
(iii). Apomixis is a cost-effective method of producing seeds.
8. Explain the significance of satellite DNA in DNA fingerprinting technique.
Short nucleotide repeats in the DNA are very specific in each individual and vary in number from person to person but are inherited. These are called the ‘Variable Number Tandem Repeats’ (VNTRs). These are also called “minisatellites”.
Role of VNTR in DNA fingerpriting: DNA fingerprinting technique for identifying individuals generally using repeated sequences in the human genome that produces a pattern of bands that is unique for every individuals. Each individual inherits these repeats from his/ her parents which are used as genetic markers in a personal identity test. For example, a child might inherit a chromosome with six tandem repeats from the mother and the same tandem repeated four times in the homologous chromosome inherited from the father. The half of VNTR alleles of the child resemble that of the mother and half that of the father.
9. Enumerate any six essentials of good, effective Dairy Farm Management Practices.
Six important ways of good and effective dairy farm management practices are as follows:
(a) Identification of improved cattle breeds is an important condition of cattle management. Hybrid cattle breeds are essential for the improved productivity. Therefore, it is necessary that hybrid cattle breeds should have a mixture of various desirable genes such as high milk yield and resistance to disease.
(b) Cattle should be fed in scientific manner with healthy and nutritious food consisting of roughage, fibre concentrates and high levels of proteins and other nutrients.
(c) They should be housed-well and kept in ventilated roofs to prevent them from heat, cold and rain.
(d) Animals should be kept in disease-free conditions. Regular bath and brushing should be ensured to control disease. Visit of a veterinary doctor is necessary on regular basis.
(e) The procedure of milking should be hygienic; emphasis should be given to storage and transportation of milk, so that the quality of milk is not affected.
(f) Regular inspection of dairy farms should be done by appointed officials to ensure that all the instructions are being strictly followed.
10. Describe any three potential applications of genetically modified plants.
Three potential applications of genetically modified (GM) plants are as follows:
(i) Pest resistance: Crop losses from insects pests can be incredible, resulting in financial loss for farmers and starvation in developing countries. Growing GM foods such as BT corn, Bt cotton etc. can help eliminate the application of chemical pesticides & reduce the cost of bringing a crop to market.
(ii) Disease resistance: There are many viruses, fungi & bacteria which cause plant diseases. Plant biologists are working to create plants with genetically engineered resistance to these diseases.
(iii) Cold tolerance: Unexpected frost can destroy sensitive seedlings. An antifreeze gene from cold water fish has been introduced into plants such as tobacco and potato.
11. How did an American Company, Eli Lilly use the knowledge of r-DNA technology to produce human insulin?
Insulin hormone is released as a pro-hormone, which consists of three peptide chains; A, B and C. This pro-hormone insulin is converted to mature insulin by removal of C peptide. The American company, Eli Lilly, used the knowledge of rDNA technology as follows:
(i) DNA sequences corresponding to the two polypeptide, A and B of insulin are synthesised in vitro.
(ii) They are introduced into plasmid DNA of E.coli.
(iii) This bacterium is cloned under suitable conditions.
(iv) The transgene is expressed in the form of polypeptidesA and B, secreted into the medium.
(v) They are extracted and combined by creating disulphide bridge to form human insulin.
12. How do snails, seeds, bears, zooplanktons, fungi and bacteria adapt to conditions unfavourable for their survival?
Snails adapt to unfavourable conditions by producing epiphragm during hibernation that covers the opening of its shell and thus prevent desiccation. Seeds adapt to unfavourable conditions by getting into the state of dormancy.
Bears adapt to unfavourable conditions by hibernation and reducing their body metabolic activities by 75%. Zooplanktons adapt to unfavourable conditions by entering into diapause (stage of suspended development).
Fungi adapt to unfavourable conditions by reducing their metabolic rate and forming thick-walled spores.
Bacteria adapt to unfavourable conditions by forming endospores.
13. Name the transcriptionally active region of chromatin in a nucleus.
Euchromatin is the transcriptionally active region of chromatin in a nucleus.
14. What is Biopiracy?
Biopiracy is unethical and illegal use of biodiversity resource of other nation without proper authorization from The countries concerned.
15. Differentiate between male and female heterogamety.
Drosophila exhibits XY type of sex determination. Males produce two types of sperms, one having X chromosome and one having Y chromosome. Whereas females have only X-type of chromosomes. Grasshoppers exhibit XO type of sex determination. Males produce two types of gametes, one with X chromosome and other with no chromosome. Thus, both show male heterogamety.
Female heterogamety is shown by female fowls as they have ZW sex-chromosomes. The ova contains 50% Z-chromosomes and other 50% ova have W-chromosomes. Hence, they also produce two types of female gametes.
CBSE Class 12 Biology Sample Paper 2018 Questions and Answers
16. State the role of microbes in sewage treatment.
Microbes clean sewage water and make it possible for us to use this water again. They effectively use up unwanted nutrients in the system, by metabolizing the solid waste that passes through the treatment plant.
17. What is plasmid?
Plasmid is an autonomously replicating circular extrachromosomal DNA used as cloning vector.
18. Name the pioneer and the climax species in a water body. Mention the changes observed in the biomass and the biodiversity of the successive seral communities developing in the water body.
(i) Pioneer species in a water body are autotrophic phytoplanktons such as diatoms, unicellur or filamentous algae, flagellates and cyanobacteria.
Climax species in a water body are trees.
(ii) Biomass and the biodiversity goes on increasing in the successive seral communities developing in the water body.
19. Mention the effects of nicotine on human body.
Nicotine stimulates adrenal glands to release adrenaline and nor-adrenaline into blood circulation, both of which increase blood pressure and heart beat rate. This lead to increased risk of heart disease.
20. Name the enzyme which is used for dissolving fungal cell wall.