Previous Year Question Paper for CBSE Class 12 Biology – 2020

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.

Overview of CBSE Class 12 Biology Paper

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).

Section A (1 Mark Each)

Qustion 1: Cleistogamous flowers are self-pollinated because

(A) they are bisexual flowers which do not open at all.

(B) they are bisexual and open flowers.

(C) they are unisexual.

(D) their stigma matures before the anthers dehisce.

Answer:

(A) Bisexual Flower which do not open at all.

OR

Asexual reproduction by zoospores is observed in

(A) Penicillium

(B) Hydra

(C) Sponge

(D) Chlamydomonas

Answer:

(D) Chlamydomonas.

Question 2: The theory of evolution supported by the experiment conducted by Louis Pasteur is

(A) Spontaneous generation theory

(B) Life comes only from pre-existing life

(C) Abiogenesis of life

(D) Big bang theory

Answer:

(B) Life comes only from pre-existing life.

Question 3: The diagnostic test that confirms typhoid in humans is

(A) ELISA

(B) Widal

(C) MRI

(D) Amniocentesis

Answer:

(B) Widal

Question 4: The bioactive molecule used as an immunosuppressive agent during organ transplant is

(A) Tetracyclin

(B) Cyclosporin-A

(C) Statin

(D) Streptomycin

Answer:

(B) Cyclosporin-A.

OR

‘Blue revolution’ refers to

(A) construction of water dams for conservation of water

(B) production of fish in large quantities

(C) sewage treatment

(D) controlling algal bloom

Answer:

(B) Production of fish in large quantities.

Question 5: Which one of the following is not the product of transgenic experiments?

(A) Pest-resistant crop variety

(B) High nutritional value in grains

(C) Production of insulin by rDNA technique

(D) Drought-resistant crops

Answer:

(No correct answer in the choices- Everyone gets one mark)

Section B (Q Nos. 6-12 are of 2 marks each)

Question 6: Write the ploidy and number of chromosomes in human (a) meiocytes, and (b) gametes.

Answer:

(a) (meiocytes) 2n, 46.

(b) (Gametes) n, 23.

Question 7: What is aneuploidy? Name a chromosomal disorder in humans caused due to (a) gain of an autosome, and (b) loss of a sex chromosome in females.

Answer:

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.

Question 8: State a functional difference between the following codons:

(a) AUG and UAA

(b) Specific and Degenerate

Answer:

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.

Question 9: (a) Identify any two marsupials from the list given below:

• (i) Lemur
• (ii) Spotted cuscus
• (iii) Flying phalanger
• (iv) Bobcat
• (v) Tasmanian wolf
• (vi) Mole

(b) “Australian marsupials exhibit adaptive radiation.’’ Justify the statement.

Answer:

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.

Question 10: Name the type of immunity the mother provides the newborn baby. How does it happen?

Answer:

Passive immunity.

Colostrum has (abundant) antibodies / IgA present

Question 11: Name the two primary lymphoid organs. State the importance of T-lymphocytes.

Answer:

Thymus, Bone marrow .

Functions: helps B-cells in production of antibodies, mediate CMI, responsible for graft rejection (any one).

Question 12: How are malignant tumors different from benign tumors? Why are some patients treated with α – interferons?

Answer:

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

Name the hormone with which a cow is administered using MOET technology. State the function of this hormone.

Answer:

Follicular Stimulating Hormone like / FSH like, to induce follicular maturation / super ovulation/production of 6-8 eggs.

Section – C (Q Nos. 13 – 22 are of 3 marks each)

Question 13: Draw a longitudinal section of the pistil from a flowering plant, where pollination has occurred. Label the following:

• (a) Stigma showing germinating pollen grains
• (b) Style
• (c) Pollen tube reaching the micropyle of the ovule
• (d) Embryo sac
• (e) Components of the egg apparatus

Answer:

14. Study the given diagram:

A is an embryonic stage that gets transformed into B, which in turn gets implanted in the endometrium in human females.

(a) Identify A, B and its parts C and D.

(b) State the fate of C and D in the course of embryonic development in humans.

Answer:

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) Identify the figure given below and also identify the parts B, C, D and E.

(b) State the function of E.

Answer:

a) Mature Dicot Embryo,

B-Suspensor; C- Radicle; D-Plumule; E-Cotyledon;

b) Storage of food reserves (as in legumes).

Question 15: A normal couple has their first child, who is haemophilic. Work out a cross to show how it is possible. State the possibility of the normal and the haemophilic children, along with their sexes, that can be born to them.

Answer:

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

Question 16: Starting from the pioneer species, trace the sequence that follows in an ecological succession on a bare rock, until climax community is reached in an ecosystem. Name this type of succession.

Answer:

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).

Question 17: The release of municipal wastewater and industrial waste into our natural water bodies is causing disastrous effect to the aquatic life. Explain the biological treatment that should be given to it before releasing into the natural water bodies.

Answer:

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.)

Question 18: Mention any two advantages of micropropagation technique. Write how its process is carried out in the laboratory. Name any two important food plants grown commercially by this method.

Answer:

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).

Qusetion 19: When Bacillus thuringiensis enters a certain insect’s body, the insect gets killed, but itself remains unaffected. Explain how it is possible.

Answer:

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.

Question 20: (a) Write how parasites have evolved with adaptation to co-exist with their hosts in an ecosystem.

(b) Parasites are host specific and tend to co-evolve. How would the parasite respond if the host evolves a certain mechanism to resist or reject the parasite?

Answer:

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) Name an ideal pyramid existing in an ecosystem. Construct it up to its three trophic levels along with their names.

(b) The sun provides 1,000,000 J of sunlight (solar energy) to an ecosystem. Write the amount of energy that is available to the first and third trophic levels, respectively.

Answer:

a) Pyramid of energy is the ideal pyramid = ½

b) (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

Question 21: Global carbon is fixed in the biosphere through photosynthesis.

(a) Explain any two ways by which carbon is returned to the atmosphere through natural processes.

(b) List any two human activities that have influenced the carbon cycle in nature.

Answer:

(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).

Section D (Q Nos. 22 – 24 are of 3 marks each)

Question 22: Study the schematic representation given above and answer the following questions:

(a) Identify A in it.

(b) Identify D in it.

(c) When the population density at time t is N as shown above, write the population density at time t + 1 in the form of an equation using appropriate symbols.

Answer:

a) A = Natality / Immigration.

b) D = Emigration / Mortality .

c) N (t+1) = Nt +[(B+I) – (D+E)].

Question 23: (a) Identify steps A and B in a cycle of Polymerase Chain Reaction given below.

(b) State the specific characteristic feature of the enzyme in carrying step B.

Answer:

a) A= Annealing; B=Extension.

b) Thermostable (DNA Polymerase) / remains active at high temperature.

Question 24: Study the diagrammatic representation of S.L. Miller’s experiment given below and answer the questions that follow:

(a) How did S.L. Miller create the conditions which existed before the origin of any life on Earth?

(b) Name the organic compound formed and collected at the end of his experiment.

(c) Mention the kind of evolution his experiment supports.

Answer:

(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.

Section E (Q Nos. 25 – 27 are of 5 marks each)

Question 25: (a) Draw the sectional view of a seminiferous tubule of human. Label its any six parts.

(b) Name the pituitary hormones involved in the process of spermatogenesis. State their functions.

Answer:

(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) IUDs are said to be effective contraceptives. Name any two commonly used IUDs and write the mode of their actions.

(b) When is sterilisation advised to married couples? How is it carried out in a human male and a female, respectively?

Answer:

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)

Question 26: Explain the expression of lac operon genes in E. coli growing in lactose containing culture medium.

Answer:

The 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

Name the types of cells and the process by which hnRNA is formed. Describe the processing mechanism it undergoes before it becomes functional.

Answer:

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.

Question 27: There is a great concern all over the world to conserve biodiversity for maintaining ecological balance in nature. Explain giving three reasons. Write different ways that have helped in increasing tiger population in our country.

Answer:

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

What is integrated organic farming? How did Ramesh Chandra Dagar, a farmer from Sonepat, Haryana effectively use this procedure and succeed with zero waste?

Answer:

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.

Conclusion – CBSE Class 12 Biology Question Paper 2020

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.

FAQs – CBSE Class 12 Biology Question Paper – 2020

Is it Necessary to Solve the CBSE Biology Previous Year Papers of Class 12?

Yes, students should try solving previous year question paper of biology before exams as it helps in analysing your preparation and give an idea about Class 12 board exams pattern.

Where I can Find CBSE Class 12 Biology Previous Year Question Paper?

You can find previous year question papers for Class 12 biology on the official website of Geeks for Geeks. We have provided accurately solved answers to all the questions.

Why Should a Student Solve the CBSE Class 12 Biology Previous Year Papers?

Solving previous year question papers of Class 12 Biology familarise them with the CBSE exam patter, marks distribution, and practise finishing writing answers within alloted time.

Are the CBSE Board Class 12 Biology Previous Year Question Papers Available with Solutions?

Yes, the previous year question papers for CBSE Class 12 Biology are available on Geeks for Geeks with solutions. The answers are provided by our experienced subject matter experts in simple language that will be easy to understand.

Is Class 12 Biology Paper Tough?

The level of difficulty of Class 12 biology paper is moderate. You can score good marks by solving Class 12 Biology Previous Year Question Papers as it helps you in understanding the pattern of the exam.