CBSE Class 12 Previous Year Question Papers With Solutions Pdf Biology

Class 12 Subject Biology Paper Set 2 with Solutions

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Question 1: (Marks 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.

OR

Asexual reproduction by zoospores is observed in

(A) Penicillium

(B) Hydra

(C) Sponge

(D) Chlamydomonas

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Answer :

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

OR

(D) / Chlamydomonas

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Question 2: (Marks 1)

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

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Answer :

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

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Question 3: (Marks 1)

The diagnostic test that confirms typhoid in humans is

(A) ELISA

(B) Widal

(C) MRI

(D) Amniocentesis

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Answer :

(B) / Widal

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Question 4: (Marks 1)

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

(A) Tetracyclin

(B) Cyclosporin-A

(C) Statin

(D) Streptomycin

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

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Answer :

(B) / Cyclosporin-A

OR

(B) / Production of fish in large quantities

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Question 5: (Marks 1)

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

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Answer :

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

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Question 6: (Marks 2)

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

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Answer :

(a) (meiocytes) 2n , 46

(b) (Gametes) n , 23

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Question 7: (Marks 2)

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.

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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

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Question 8: (Marks 2)

State a functional difference between the following codons :

(a) AUG and UAA

(b) Specific and Degenerate

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Answer :

a. AUG – Start codon / codes for Methionine / Met , UAA- Stop / codon / Nonsense Codon / Does not code for any aminoacid / Terminator Codon / Ochre

b. Specific - one codon codes for one amino acid

Degenerate - one amino acid coded by more than one codon

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Question 9: (Marks 2)

(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.

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Answer :

a. ii ) / Spotted cuscus,

iii) / Flying phalanger

v) / Tasmanian wolf

(Any two)

b. Australian marsupials each differ from the other evolved from an ancestral stock, all within the Australian island continent.

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Question 10: (Marks 2)

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

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Answer :

Passive immunity

Colostrum has (abundant) antibodies / IgA present

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Question 11: (Marks 2)

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

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Answer :

Thymus , Bone marrow

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

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Question 12: (Marks 2)

How are malignant tumours different from benign tumours ? Why are some patients treated with α-interferons ?

OR

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

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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

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

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Question 13: (Marks 3)

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

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Answer :

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Question 14: (Marks 3)

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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) Mature Dicot Embryo,

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

b) Storage of food reserves (as in legumes)

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Question 15: (Marks 3)

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.

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Answer :

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Question 16: (Marks 3)

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.

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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)

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Question 17: (Marks 3)

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.

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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.)

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Question 18: (Marks 3)

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.

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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)

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Question 19: (Marks 3)

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

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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.

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Question 20: (Marks 3)

(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 ?

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.

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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

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Question 21: (Marks 3)

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.

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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)

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Question 22: (Marks 3)

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.

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Answer :

a) A = Natality / Immigration -

b) D = Emigration / Mortality

c) N (t+1)=Nt+[(B+I)-(D+E)

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Question 23: (Marks 3)

(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.

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Answer :

a) A= Annealing; B=Extension

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

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Question 24: (Marks 3)

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.

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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

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Question 25: (Marks 5)

(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.

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 ?

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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) - 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)

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Question 26: (Marks 5)

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

OR

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

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Answer :

In the presence of an inducer , lactose , the repressor is inactivated , by interaction with the inducer, this allows RNA polymerase access to the promoter , and transcription proceeds , lac mRNA is transcribed , ß galactosidase , permease , transacetylase is synthesised.

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.

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Question 27: (Marks 5)

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.

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 ?

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Answer :

Biodiversity should be conserved for the following three reasons:

a) Narrowly utilitarian -

humans derive countless economic benefits from nature-

e.g. food (cereals, pulses, fruits) / firewood / fibre / construction material / industrial products (tannins, lubricants , dyes , resins , perfumes) / products of medicinal importance. (any one)

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

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