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CBSE Class 12 Biology Previous Year Question Paper helps you to understand the level of questions asked in the previous exams, along with the changes in pattern. Practicing the previous year's question paper for CBSE Class 12 Biology enhances time-management skills while appearing in the board examination. It makes you understand the importance of different topics that have been asked previously.
Previous year’s CBSE Class 12 Biology Question Papers will boost your confidence level to appear in the examination with proper knowledge of different topics that are going to be asked. It enhances the understanding of the topic and acts as a checkpoint to see the level of preparation that you have done. CBSE Class 12 Biology Question Papers 2020 is available here.
A detailed overview of the CBSE Class 12 Biology paper – 2020 is given below:
Sections | Question Types | No. of Questions |
|---|---|---|
Section A (1m) | Multiple Choice Questions | 5Q (5m) |
Section B (2m) | Short Answer-type Questions I | 7Q (14m) |
Section C (3m) | Short Answer-type Questions II | 9Q (27m) |
Section D (3m) | Short Answer-type Questions III | 3Q (9m) |
Section E (5m) | Long Answer-type Questions | 3Q (15m) |
This pattern indicated that there were 27 questions total in the Biology 2020 Paper, which were broken down into five sections: A, B, C, D, and E. There were a lot of internal options available to students (even in MCQs).
(A) Bisexual Flower which do not open at all.
OR
(D) Chlamydomonas.
(B) Life comes only from pre-existing life.
(B) Widal
(B) Cyclosporin-A.
OR
(B) Production of fish in large quantities.
(No correct answer in the choices- Everyone gets one mark)
(a) (meiocytes) 2n, 46.
(b) (Gametes) n, 23.
Failure of segregation of chromatids (during cell division), resulting in gain or loss of a chromosome (s).
(a) (Gain of an autosome) - Down’s syndrome.
(b) (Loss of a sex chromosome) - Turner’s syndrome.
a) AUG – Start codon / codes for Methionine / Met, UAA- Stop / codon / Nonsense Codon/ Does not code for any amino acid / Terminator Codon / Ochre.
b) Specific - one codon codes for one amino acid.
Degenerate - one amino acid coded by more than one codon.
a. ii) Spotted cuscus, iii) Flying phalanger, and v) Tasmanian wolf.
b. Australian marsupials each differ from the other evolved from an ancestral stock, all within the Australian island continent.
Passive immunity.
Colostrum has (abundant) antibodies / IgA present
Thymus, Bone marrow .
Functions: helps B-cells in production of antibodies, mediate CMI, responsible for graft rejection (any one).
Benign tumors remain confined to their original location/ do not spread to other part of the body / cause little damage / no metastasis, malignant tumors proliferate and spread to other body parts / is more harmful / cause serious damage/ causes metastasis.
Biological response modifiers / activate immune system to destroy tumor.
OR
Follicular Stimulating Hormone like / FSH like, to induce follicular maturation / super ovulation/production of 6-8 eggs.
a) A - Morula; B - Blastocyst; C - Inner cell mass / Stem cells, D - Trophoblast.
b) C. (Inner cell mass) forms embryo / differentiates into germ layers (ectoderm / mesoderm / endoderm), D. Trophoblast helps in attachment of embryo / to endometrium / forms chorionic villi / forms placenta.
OR
a) Mature Dicot Embryo,
B-Suspensor; C- Radicle; D-Plumule; E-Cotyledon;
b) Storage of food reserves (as in legumes).
The bleeding disorder hemophilia comes from a hereditary incapacity of the blood to clot correctly. Both spontaneous bleeding and bleeding following surgery or an injury may result from this. Blood proteins called clotting factors can stop bleeding.
Here,
Carrier Female = XXh
Normal Male = XY
Lichens are the pioneer species on rocks, they secrete acid and dissolve rocks help in soil formation, pave way to bryophytes that hold small amount of soil, succeeded by higher plants / and scrub, after several stages a stable climax forest community is formed.
Primary Succession / Xerarch (succession).
The primary effluent is passed into large aeration tanks where it is mechanically constantly agitated and air is pumped into it, this allow growth of useful aerobic microbes into Flocs / masses of bacteria associated with fungal filaments, these microbes consume major part of organic matter in the effluent reducing BOD, effluent is passed into settling tanks where Flocs are allowed to sediment called activated sludge , a small part of this is pumped back into the aeration tank to serve as the inoculum , the remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters where anaerobic bacteria digest the bacteria and the fungi in the sludge. (During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide.)
Used for the production of large number of plants that are genetically identical to the original plant, recovery of healthy plants from diseased plant.
Any part of the plant /explant is grown in the test tube under sterile conditions, in specified nutrient media (sucrose, inorganic salts, vitamins, amino acids, growth hormones - Auxin and cytokinin).
Potato / Banana / sugarcane / tomato / apple (any two).
B. thuringiensis forms protein crystals which contain a toxic insecticidal protein, Bt toxin protein remains as inactive protoxin, once an insect ingests the inactive toxin, it is converted into an active form of toxin due to alkaline pH of the gut, the activated toxin binds to midgut epithelial cells, and creates pores that cause swelling and lysis of the cells.
a) Loss of unnecessary sense organs, presence of adhesive organs / suckers, loss of digestive system, high reproductive capacity.
b) (If the host evolves special mechanism for rejecting or resisting a parasit) the parasite has to evolve a mechanism to counteract and neutralize them.
OR
a) Pyramid of energy is the ideal pyramid = ½
👁 Q--20b) (from sun to primary producer 1%)
10,00,000J from sun, (1%) = 10,000 J
10,000 J → 1000J → 100 J
First trophic level Third trophic level
(a) Natural process - Respiration by plants and animals, decomposition (bacteria, fungi).
(b) Human activities - burning of fossil fuel / burning of forest fuel wood / burning of leaves (any two).
a) A = Natality / Immigration.
b) D = Emigration / Mortality .
c) N (t+1) = Nt +[(B+I) - (D+E)].
a) A= Annealing; B=Extension.
b) Thermostable (DNA Polymerase) / remains active at high temperature.
(a) (Conditions existed before the origin of life - High temperature, volcanic storms, reducing atmosphere containing CH4, NH3, etc.). Conditions were created by electric discharge (high temperature) in a closed flask containing CH4, NH3, H2, water vapours.
b) Amino acids.
c) Chemical evolution.
(a)
b) Pituitary hormones: Luteinising hormone (LH) , follicle stimulating hormone (FSH). (LH) Acts at the leydig cells and stimulates synthesis and secretion of androgens. (FSH) Acts on sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.
OR
a) Lippes Loop, - increases phagocytosis of sperms within the uterus- CuT / Cu7 / Multiload 375, - Cu ions suppress sperm motility/ fertilising capacity of sperms.
Progestasert / LNG - 20, - makes uterus unsuitable for implantation / makes cervix hostile to sperms (any two IUDs with their related actions)
b) Sterilization advised for the male /female partner as terminal method to prevent any more pregnancies.
In male: part of vas deferens is cut and tied (vasectomy) In female: a small part of the fallopian tube is removed or tied up (tubectomy)
👁 lac-operonThe lac operon of E. coli contains genes involved in lactose metabolism. It is expressed when lactose is present but glucose is not. Two regulators that control the operon's "on" and "off" responses to lactose and glucose levels are the catabolite activator protein and the lac repressor (CAP).
The lac repressor detects lactose. It fails to function as a repressor and prevents the operon's transcription when lactose is present. The lac repressor detects lactose indirectly through its isomer allolactose.
A glucose sensor is called catabolite activator protein, or CAP. Low glucose levels cause the operon's transcription to become active. By use of the "hunger signal" chemical cAMP, CAP indirectly senses glucose.
Although the bacteria E. coli can break down lactose, it is not their preferred energy. If glucose is available to them, they would much rather use it. Compared to glucose, lactose requires less energy and breaks down in fewer steps. However, E. Coli will immediately use lactose as an energy source if it is the only form of sugar present.
When lactose, is present, the repressor is inactivated by contact with the inducer, giving RNA polymerase access to the promoter and transcription to begin. The synthesis of B galactosidase, permease, and transacetylase occurs after the transcription of lac mRNA.
OR
hn RNA is formed in eukaryotic cells, during transcription.
Primary transcript contains both exon, introns is non-functional, it is subjected to splicing, where intros are removed, exons are joined in a defined order, hn RNA undergoes capping with nucleotide (methyl guanosine triphosphate) being added to the 5’- end of hn RNA,
In tailing, adenylate residues (200-300) are added at 3’-end in a template independent manner.
Biodiversity should be conserved for the following three reasons:
a) Narrowly utilitarian - humans derive countless economic benefits from naturee.g. food (cereals, pulses, fruits) / firewood / fibre / construction material / industrial products. (tannins, lubricants, dyes, resins, perfumes) / products of medicinal importance.
b) Broadly utilitarian - Play role in many ecological services e.g. production of O2 / pollination / Aesthetic pleasures.
c) Ethical - Every species has an intrinsic value / we have a moral duty to care for their well-being/ pass on our biological legacy in good order to future generations.
The two approaches to save tiger is:
a) In situ conservation– protect the natural habitat the forest where the tiger lives / protect the whole ecosystem to save tigers
b) Ex situ conservation - threatened tigers are taken out of their natural habitat and placed in special settings for protection and special care / e.g. zoological park, wildlife sanctuaries.
OR
Integrated organic farming is a cyclical procedure where waste products from one process are cycled in as nutrients for another process. His farm includes bee-keeping, dairy management, water harvesting, composting, agriculture in a chain of processes. There is no need to use chemical fertilizers, as cattle excreta (dung) is used as manure / natural fertilizer, Crop waste can be used to create compost, to generate natural gas for satisfying the energy needs of the farm.
The previous year question paper for CBSE Class 12 Biology are an important tool for preparing for CBSE Class 12 Board Examinations. Students who practice many previous year question paper can learn useful tips that will assist them in scoring good marks in CBSE Class 12 Biology exam. The main purpose of providing the previous year question papers is to give an idea about exam pattern and the types of questions asked in exam. Questions are often repeated in exams as well. Hence, solving class 12 previous year question paper for biology is important while studying.
