Central Board of Secondary Education ,New Delhi is one of the renowned institution and a huge number of schools in India which are affiliated by this board .For over the years CBSE schools have been recognized as the best education and so many students are now going for CBSE board as compared to other boards at secondary and higher secondary level as its performance level has excelled. Here in this post as an Engineer, I have tried to prepared Solved CBSE Sample Papers for Class 12 Biology students which is based on CBSE Board syllabus which all most cover all important topics that regularly asked in the exam that will help you for the preparation. So, practice as much as you can.
General Instruction to be followed:
a) There are 30 questions and four section.
b) Questions 1-10 carry one mark each.
c) Questions 11-20 carry two mark each.
d) Questions 21-26 carry three mark each.
e) Questions 27-30 carry five mark each.
SECTION-I [I ONE MARK QUESTIONS]
1) How many male gametophytes this anther can produce when a bilobed, dithecous anther has 100 microspore mother cells per microsporangium? [1 mark]
Ans : Male gametophytes produced are 1600
2) Explain why honey collection improves when beehives are kept in crop-fields during flowering season. [1 mark]
Ans : Bees visit flowers for collecting nectar more the number of flowers larger is the nectar.
3) Give the name of the scientist who disproved spontaneous generation theory. [1 mark] Ans : The name of the scientist is Louis Pasteur.
4) State functions of the codon AUG. [1 mark] Ans : Functions of the codon AUG are Initiator Codon, codes for Methionine
5) Give one most preferred one reason which make what is it that prevents a child to suffer from a disease he/she is vaccinated against? [1 mark] Ans : Antibodies produced kills pathogen and prevents disease.
6) Give the name of a molecular diagnostic technique to detect the presence of a pathogen in its early stage of infection. [1 mark] Ans : Recombinant DNA technology
7) Give reason why is the enzyme cellulose used for isolating genetic material from plant cells but not for animal cells? [1 mark] Ans : Animal cells do not have cellulose cell walls, plant cell have cellulose in their cell wall.
8) What would be the death rate for population for the said period if 8 individuals in a laboratory population of 80 fruitflies died in a week, then? [1 mark] Ans : 0.1 individuals per fruitfly per week
9) Give the name of the type of cell division that takes place in the zygote of an organism exhibiting haplontic life cycle. [1 mark] Ans : The name of the type of cell division that takes place in the zygote of an organism exhibiting haplontic life cycle is Meiosis.
10) Give the name of the event during cell division cycle that results in the gain or loss of chromosome. [1 mark] Ans : Failure of segregation of chromatids.
SECTION-II [ TWO MARK QUESTIONS]
11) Explain how does an electrostatic precipitator work to remove particulate pollutants released from the thermal power plants? [2 mark] Ans : Electrode wires at several thousand volts produce a corona that releases electrons electrons attach to dust particles , become negatively charged , are attracted to collecting plates , low velocity of air help settling of dust.
12) State one positive and one negative application of amniocentesis. [2 mark] Ans : One positive application of amniocentesis is to detect genetic disorders and one negative application is it may lead to illegal female foeticide .
13) State why is the introduction of genetically engineered lymphocytes into a ADA deficiency patient not a permanent cure? Also give a permanent cure for it. [2 mark] Ans : Lymphocytes not immortal thus patient requires periodic infusion of such genetically engineered lymphocytes , though if a gene producing ADA is isolated from marrow cells and introduced into the cells at early embryonic stages it could be a permanent cure
14) Explain any two levels of biodiversity as in the biosphere immense biological diversity exists at all levels of biological organisation. [2 mark]
Ans : Species diversity: The diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
Ecological diversity: At the ecosystem level, India, for instance, with its deserts or rain forests coral reefs or estuaries and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway.
15) Illustrate about convergent and divergent evolution. [2 mark]
Ans : Convergent – Different structures evolving in the same direction in different organisms eg. wings of butterfly and of birds or eye of octopus and of mammals and dolphins.
Divergent – Same structure evolving in different directions in different organisms eg. forelimbs of whales, bats, cheetah and humans.
16) Mention the efforts which must be put in to improve health, hygiene and milk yield of cattle in a dairy farm. [2 mark] Ans : Should be taken to veterinary doctor,housed well,have adequate water,be maintained disease free,feeding should be carried out keeping quality and quantity of fodder in mind,maintain stringent cleanliness and hygiene .
17) Illustrate the initiation process of transcription in bacteria. [2 mark] Ans : RNA polymerase,binds to the promoter at 5’ end,associates transiently with initiation factor, using nucleoside triphosphates as substrate and energy initiates transcription.
18) State how a hereditary disease can be corrected also give an example of first successful attempt made towards correction of such diseases. [2 mark] Ans : Prologue of required genes into cells and tissues to treat diseases by delivery of normal gene to take over the function of non-functional gene by gene therapy. First gene therapy was given to four year old girl with Adenosine deaminase deficiency.
19) Give the reasons for difference in ploidy of zygote and primary endosperm nucleus in an angiosperm. [2 mark] Ans : Zygote formed by the fusion of male gamete (n) and egg cell (n) thus diploid (2n) Primary endosperm nucleus formed by the fusion of secondary nucleus (n + n) and male gamete (n) thus triploid (3n) formed.
20) Explain how does a testcross help in identifying the genotype of the organism? [2 mark] Ans : Cross between an organism with unknown genotype and an organism with recessive trait. If all offsprings show dominant trait the organism is homozygous, if half organisms show dominant and half recessive then the organism is heterozygous.
SECTION-III [THREE MARK QUESTIONS]
21) Illustrate the process of RNA interference. [3 mark] Ans : This method involves silencing of a specific mRNA of the parasite due to complementary dsRNA molecule that binds to and prevents translation of the mRNA .The source of this complementary RNA could be from an infection from viruses having RNA genomes or mobile genetic elements that replicate via RNA intermediate .
22) State how does RNA interference help in developing resistance in tobacco plant against nematode infection? [3 mark] Ans : With RNA interference technique transgenic tobacco plant is protected against nematode meloidogyne incognita using Agrobacterium as the vectors,nematode-specific genes were introduced into the host plant than it produces both sense & antisense RNA, these 2 RNAs form dsRNA, it silences specific mRNA of nematode thus nematode cannot survive in tobacco plant.
23) State how are dominance, codominance and incomplete dominance patterns of inheritance different from each other? [3 mark]
Ans : Dominance : One allele expresses itself in the hybrid heterozygous condition , other is Suppressed.
Co dominance : Both the alleles of a gene express in a heterozygous hybrid containing two Dominant alleles.
Incomplete dominance : Neither of the two alleles of a gene is completely dominant over the other in heterozygous condition the hybrid is intermediate.
24) Give the name of the two types of immune systems in a human body also state why is it known as cell mediated. [3 mark] Ans : Two types of immune systems are Active and Passive immune system .Cell mediated immunity is called so because cells like T-lymphocytes provide immunity or destroy the antigens.
25) Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution also explain each concept with the help of a suitable example. [3 mark]
Ans: Branching descent:Different species descending from the common ancestor get adapted in different Habitats.
e.g. Darwins finches – varieties of finches arose from grain eaters or Australian marsupials – evolved from common marsupial .
Natural selection : A process in which heritable variations enable better survival of a species to reproduce in large number.
26) (a)State why is CuT considered a good contraceptive device to space children ?
(b) State what is inbreeding depression and how is it caused in organisms also mention two advantages of inbreeding. [3 mark] Ans: (a) CuT is considered a good contraceptive device to space children as Non-hormonal, non-medicated,releases Copper ions, suppresses sperm motility, suppresses fertilising capacity of sperms, phagocytosis of sperms.
Ans: (b) Continuous close inbreeding for several generations, reduces fertility and productivity is known as inbreeding depression. Its advantages are it produces pure lines and accumulation of superior genes.
SECTION-IV [FIVE MARK QUESTIONS]
27) Give reasons why : [5 mark]
(i) Most zygotes in angiosperms divide only after certain amount of endosperm is formed.
(ii) Groundnut seeds are albuminous and castor seeds are albuminous.
(iii) Micropyle remains as a small pore in the seed coat of a seed.
(iv) Integuments of an ovule harden and the water content is highly reduced, as the seed matures.
(v) apple and cashew are not called true fruits.
Ans.(i) To obtain nutrition from the endosperm for the developing embryo
(ii) Ground nut – endosperm completely consumed castor – endosperm persists.
(iii) For the entry of water, for germination.
(iv) Protect the embryo, until favorable conditions return for germination
(v) Ovary is not taking part in fruit formation contributes to fruit formation .
28) If a desired gene is identified in an organism for some experiments, explain the process of the following :[5 mark]
(i) Cutting this desired gene at specific location
(ii) Synthesis of multiple copies of this desired gene
- Identifying the restriction endonuclease that recognises the palindromic nucleotide sequence of the desired gene.
- The restriction endonuclease inspects the DNA sequences – finds and recognises the site
- Cuts each of the double helix at the specific point – a little away from the centre of the palindromic site – between the same two bases on the opposite strand
- Makes the overhanging stretch single stranded portion as a sticky end.
(ii)-By PCR / Polymerase Chain Reaction
- – Desired gene is synthesised in vitro
- – DNA is denatured
- – Annealed using two sets of primers
- – Thermostable Taq polymerase extends the primers using nucleotides
- – Amplified fragments are ligated
29) (i) Describe the characteristics a cloning vector must possess. [5 mark]
(ii)Why DNA cannot pass through the cell membrane ? Explain. How is a bacterial cell made ‘competent’ to take up recombinant DNA from the medium ?
Ans.(i) The characteristics are :
- Should have origin of replication.
- Has selectable marker, genes encoding for an antibiotic resistance – galactosidase.
- Has cloning site, for the restriction enzyme to recognise.
(ii) DNA is a hydrophilic molecule. Bacterial cell is made competent by treating with specific concentration of Ca-ion, incubating them on ice, heat shock for a short period and placing it back on ice again .
30) (a) Explain primary productivity and the factors that influence it. [5 mark]
(b) Describe how do oxygen and chemical composition of detritus control decomposition.
Ans.(a) Primary productivity : Amount of biomass produced per unit area over a time period by the plant during photosynthesis .
Factors : Availability of nutrients ,availability of water, temperature of the given place, type of plant species of the area,photosynthetic capacity of the plants .
(b) Oxygen increases rate of decomposition.Chemical: Decomposition is slow when chitin and lignin are present.
Related Links for pdf of Biology Sample Papers for Class 12 CBSE :
- CBSE Sample Papers for Class 12 Biology 201
- Solved Biology Sample Papers for Class 12 CBSE
- Biology CBSE Class 12th Sample Papers 2012
- CBSE Sample Paper for Class 12 Biology
Related Links for Sample Papers for Class 12 CBSE :
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BEST OF LUCK FOR EXAM PREPARATIONS…!!