Please see below Class 12 Biology Sample Paper Set B with solutions. We have provided Class 12 Biology Sample Papers with solutions designed by Biology teachers for Class 12 based on the latest examination pattern issued by CBSE. We have provided the following sample paper for Class 12 Biology with answers. You will be able to understand the type of questions which can come in the upcoming exams.

CBSE Sample Paper for Class 12 Biology Set B

SECTION – A

1. State two methods of apomictic development in seeds.
Answer : The two common methods of apomictic development are recurrent agamospermy and adventive embryony.

2. What will be the ploidy level of cells of endothecium, tapetum, sporogenous tissue and microspore tetrads respectively?
Answer : Endothecial cells – 2n Tapetal cells – Most of the mature tapetal cells are multinucleate and are polyploid. Cells of sporogenous tissue – 2n Cells of microspore tetrads or microspores – n

3. Name the hormones which stimulate milk production and milk ejection respectively.
Answer : Milk production is stimulated by hormone prolactin and ejection of milk is stimulated by oxytocin.

4. In the given diagrammatic representation of the transcription “unit”, what do the parts P and Q represent?

Answer : P → Promoter Q → Coding strand

5. On what basis is the skin colour in humans considered polygenic?
Answer : The skin colour of human is controlled by three genes where the dominant alleles have cumulative effect. Each dominant allele expresses a part or unit of the trait (skin colour). Such type of genes are called polygenes and their inheritance is called as polygenic inheritance. So, the skin colour of human is a polygenic trait.

6. State the fate of a pair of autosomes during gamete formation.
Answer : During gamete formation a diploid germinal cell changes to a haploid germ cell. Hence, a pair of autosomes get segregated by means of meiotic division to produce haploid gametes.

7. Why is RNA more reactive in comparison to DNA?
Answer : RNA is more reactive in comparison to DNA because: (i) 2′ –OH group present in ribose sugar of every nucleotide of RNA is a reactive group. It makes RNA highly reactive, labile and easily degradable. (ii) RNA functions as an enzyme, therefore is reactive and unstable.

8. There are three types of restriction endonucleases. Which among the three is/are used in recombinant DNAtech nology?
Answer :  Three types of restriction endonucleases are type I, type II and type III. Only type II restriction enzymes are used in rDNA technology. 

9. Name the transgenic plant from which hirudin is extracted.
Answer : Brassica napus

10. Which type of biological interaction is present between sucker fish and shark?
Answer : The biological interaction between sucker fish and shark is an example of commensalism.

11. Assertion : ADA deficiency cannot be cured permanently by gene therapy.
Reason : The genetically engineered lymphocytes are immortal only in culture conditions.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : D

OR

Assertion : PCR is routinely used for early diagnosis of HIV in suspected AIDS patients.
Reason : PCR can detect low amounts of DNA.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : B

12. Assertion : In secretory tapetum, the tapetal cells fuse to form a plasmodium because it passes in between the sporogenous cells to nourish them.
Reason : The cells of amoeboid tapetum pass out substances over the sporogenous cells for their growth and differentiation.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : D

13. Assertion : Periodic migration occurs in Arctic tern when their number increases beyond the feeding capacity of the homeland.
Reason : Arctic tern migrate in search of food.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : D

14. Assertion : Maximum biodiversity occurs in temperate areas.
Reason : Temperate areas have favourable conditions for speciation and for supporting variety and number of organisms.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : D

15. Read the following and answer any four questions from 15(i) to 15(v) given below:
Biodiversity refers to diversity at all levels of biological organisation ranging from macromolecules inside the cells to biomes. There are three levels of diversity ; bacteriophage with 100 genes and E.coli with 400 genes show diversity X. It is related to number of genes and their allele found in organisms. Diversity Y is shown by a community having three different species represented by 4, 1 and 1 individuals and a community having three bird species with two individuals of each species related to number and distribution of species found in an area. Deserts, rainforests, coral reefs, etc. show diversity Z. It represents variety of forms in the ecosystem due to diversity of niches, trophic levels and ecological processes.

(i) Which diversity is shown by varieties of rice and mango?
(a) X, genetic diversity
(b) Y, species diversity
(c) Z, α-ecological diversity
(d) X, Y-diversity
Answer : A

(ii) Which of the following statements is incorrect?
(a) Genetic diversity is trait of species.
(b) Species diversity is the variety in the number and richness of species of a region.
(c) Beta diversity is a species diversity in a given community or habitat.
(d) Species diversity influences biotic interactions.
Answer : C

(iii) __________ is the number of species per unit area, while number of individuals of different species represent __________ .
(a) species evenness, species richness
(b) species richness, species evenness
(c) species evenness, species equitability
(d) species evenness, species unevenness
Answer : B

(iv) Select the correct option for diversity Y.
(a) It is a trait of the community.
(b) It influences biotic interactions.
(c) It is related to number and distribution of species.
(d) All of these
Answer : D

(v) Assertion : Diversity helps in producing stable ecosystems.
Reason : Diverse communities can tolerate adverse environmental conditions.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : A

16. Read the following and answer any four questions from 16(i) to 16(v) given below:
While studying about the structure of human genetic material, DNA in the class, teacher taught the class about hydrogen bonding between complementary bases of antiparallel nucleotide chains. A student asked the teacher about detailed double helical structure of DNA and its X-ray crystallographic structure.

(i) What is the pitch of helix per turn?
(a) 3.4 nm
(b) 34 nm
(c) 0.34 nm
(d) 3.4 Å
Answer : A

(ii) Identify the number of hydrogen bonds present between complementary bases.
(a) A = T ; C = G
(b) A – T ; C – G
(c) A – T ; C = G
(d) A = T ; C ≡ G
Answer : D

(iii) Select the correct statement regarding DNA.
(a) Watson and Crick proposed double helical structure of DNA through X-ray diffraction.
(b) Two chains of DNA are parallel to each other in same direction.
(c) Two chains of double helix have sugar phosphate backbone and nitrogen bases on inner side.
(d) DNA shows conservative replication as both strands function as template.
Answer : C

(iv) If sequence of one chain of DNA is AAGCTCAG, then what would be the sequence of complementary strand?
(a) TTGCAGTC
(b) TTCGAGTC
(c) TTCCAGTC
(d) TTCGAGTG
Answer : B

(v) Assertion : Two chains of DNA run parallel but in opposite direction.
Reason : Direction in one chain is 5′ → 3′ and in other is 3′ → 5′.
(a) Both assertion and reason are true, and reason is the correct explanation of assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Both assertion and reason are false.
Answer : A

SECTION – B

17. A bilobed dithecous anther contains 50 pollen mother cells (PMCs) per microsporangium. How many male gametophytes can be produced by this anther?
Answer : A bilobed dithecous anther consists of four microsporangia. In the given case, each microsporangium contains 50 pollen mother cells (PMCs), therefore total 200 PMCs will be present in this anther. As each PMC produces 4 pollen grains which develop into 4 male gametophytes, therefore, pollen grains or male gametophytes produced by this anther will be 800 (=200 × 4).

18. How does a single t RNA type recognise more than one codon on mRNA?
Answer : According to the Wobble hypothesis, only the first two positions of a triplet codon on mRNA have a precise pairing with the base of the tRNA anticodon. The pairing of the third position basis of the codon may be ambiguous and varies according to the nucleotide present in this position. Thus, a single tRNA type is able to recognise two or more codons differing only in the third base (wobble position).

19. Briefly describe cyclosporin-A.
Answer : Cyclosporin A is an eleven membered cyclic oligopeptide obtained through fermentive activity of fungus Trichoderma polysporum. It has antifungal, anti-inflammatory and immunosuppressive properties. It inhibits activation of T cells and therefore prevents rejection reactions in organ transplantation.

20. Explain how ‘Rosie’ is considered different from a normal cow.
Answer : Rosie is the first transgenic cow which produces human protein enriched milk. The milk contains human alpha-lactalbumin. This milk is nutritionally more balanced for human babies than natural cow milk.

21. (a) What is a bioreactor? Mention an advantage and a disadvantage of it.
(b) Name the types of commonly used bioreactors.
Answer : (a) A bioreactor is a vessel in which raw materials are biologically converted into specific products by microbes, plant and animal cells and their enzymes. It provides optimal growth conditions (temperature, pH, substrate, salt, vitamins, oxygen) to the microbes for the synthesis of desired product. Advantage of bioreactor is that it is well suited for large-scale production of microorganisms under aseptic conditions for a number of days. A major drawback or disadvantage of bioreactor is that it is relatively expensive to run it. 
(b) The most commonly used bioreactors are of stirring type and these are of two types :
(i) Simple stirred – tank bioreactor (ii) Sparged stirred – tank bioreactor 

OR

In the experiment of cloning a gene, what would be the effect of a plasmid without a selectable marker?
Answer : If a cloning vector does not have a selectable marker, then it would not be possible to distinguish between transformants (host bacterium having rDNA) and non-transformants. Therefore, an ideal cloning vector should have selectable markers for the selection of transformants.

22. Explain the nature of the given gene sequence.
5′ – GAATTC – 3′
3′ – CTTAAG – 5′
Answer : Palindromes are groups of letters that form the same words when read both forward and backward, e.g., “MALAYALAM”. As against a word-palindrome where the same word is read in both directions, the palindrome in DNA is a sequence of base pairs that reads same on the two strands when orientation of reading is kept the same. For example, the following sequences read the same on the two strands in 5′ → 3′ direction. This is also true if read in the 3′ → 5′ direction. In this case, it is 5′ — GAATTC — 3′ 3′ — CTTAAG — 5′.

OR

What is the contribution of Cohen and Boyer in the field of biotechnology?
Answer : Cohen and Boyer contributed to the field of biotechnology by constructing the first recombinant DNA molecule in 1972. They cut the piece of DNA from a plasmid carrying antibiotic resistance gene in Salmonella typhimurium. This piece of foreign DNA, was linked with the plasmid DNA, acting as a vector with the help of enzyme DNA ligase and introduced into E. coli.

23. Name the plant source of ganja. How does it affect the body of the abuser?
Answer : Ganja is obtained from Cannabis sativa. It is hallucinogenic. It alters thoughts, feelings and perceptions and causes illusions.

24. How do mycorrhizae act as biofertilisers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants.
Answer : Mycorrhiza is a mutually beneficial or symbiotic association of a fungus with the roots of a higher plant. The most common fungal partners of mycorrhiza are Glomus species. Mycorrhizal roots show a sparse or dense woolly growth of fungal hyphae on their surface. They perform several functions for the plant –
(i) Absorption of water, (ii) Solubilisation of organic matter of the soil humus, release of inorganic nutrients, absorption and their transfer to root.
(iii) Direct absorption of minerals from the soil over a large area and handing over the same to the root. Plants with ectomycorrhiza are known to absorb 2–3 times more of nitrogen, phosphorus, potassium and calcium.
(iv) The fungus secretes anti-microbial substances which protect the young roots from attack of pathogens.

25. Differentiate between parasitism and competition, giving one example of each. State the common characteristic they share.
Answer :  Differences between parasitism and competition are as follows:

Both parasitism and competition are negative population interactions. In parasitism, one organism (parasite) has negative effect on other organism (host) and in competition, both species are negatively affected.

SECTION – C

26. Answer the given questions based on following figures.

(i) Identify the devices P and Q.
(ii) What are their utility?
Answer : (i) P and Q are copper releasing intrauterine devices (IUDs). P is CuT and Q is multiload 375. (ii) P and Q are used as effective methods of birth control. They are inserted by doctors or expert nurses in the uterus through vagina. IUDs increase phagocytosis of sperms within the uterus and the Cu ions released by them suppress sperm motility and fertilising capacity of the sperms.

27. Incomplete dominance is not an example of pre-Mendelian concept of blending inheritance. Justify the statement.
Answer : Incomplete dominance is the phenomenon in which neither of the two contrasting alleles of a gene is completely dominant over the other. Therefore, the expression of character controlled by the particular gene in F1 individual is intermediate or fine mixture of the expression of two alleles. For example in Mirabilis, on crossing red flowered plants with white flowered plants, pink-flowered plants (intermediate) are obtained in F1 generation. On selfing F1 plants, all red, pink and white flowered plants appear in F2 generation in the ratio of 1 : 2 : 1. The occurrence of parental characters in F2 generation indicates that the alleles do not blend when present together in F1 generation and therefore, segregate at the time of gamete formation. Hence, it cannot be considered a case of blending inheritance.

OR

Refer to the given figure and answer the following questions.  

(i) Identify the genotype for the individuals P, Q, R, S and T in the given figure.
(ii) Briefly describe the characteristics of the trait traced in the given figure.
Answer : (i) P – Aa, Q – aa, R – Aa, S – aa, T – aa (ii) The trait illustrated in the given figure is an autosomal recessive trait. It appears in case of marriage between two heterozygous individual (Aa × Aa), a recessive individual with hybrid (Aa × aa) and two recessive (aa × aa). For example, fused ear lobe, alkaptonuria, etc.

28. Mention the special adaptations evolved in parasites and why?
Answer : Parasitism is a negative interaction wherein parasite depends on its host organism partially or completely for survival and perpetuation. Accordingly, parasites are classified as partial or hemiparasites and complete or holoparasites. Also they could be ectoparasites (on host’s body) or endoparasites (inside host’s body). Parasites are adapted vividly on the basis of their dependability on host. In accordance with their life styles, parasites evolved special adaptations such as:
(i) Anaerobic respiration in internal parasites
(ii) Loss of unnecessary sense organs (iii) Presence of adhesive organs (e.g., suckers in tapeworm) to cling on to the host
(iv) Loss of certain organs (e.g., bedbugs lack wings, Taenia loses digestive system)
(v) Excessive multiplication
(vi) Resistant cysts and eggs for safe transfer of their progeny to new hosts
(vii) High reproductive capacity.

29. (a) How is mature insulin different from proinsulin secreted by pancreas in humans?
(b) How human functional insulin is produced using rDNA technology?
(c) Why is the functional insulin thus produced, considered better than the ones used earlier by diabetic patients?
Answer : (a) Proinsulin has A, B and C polypeptide strands. It is non-functional. The mature insulin has only A and B polypeptide strands and it is functional.
(b) From the human cell, DNA containing insulin gene is isolated. The two DNA sequences corresponding to A and B chains of human insulin is introduced into the plasmids of E. coli to produce insulin chains A and B. The extracted chains A and B are combined by creating disulphide bonds to form human insulin (humulin).
(c) The insulin prepared by rDNA technology does not produce sensitive allergic reactions and immunological reactions. Those insulin used earlier, produced allergic reactions and other complications to the foreign protein as earlier insulin were extracted from pancreas of slaughtered cattle and pigs.

30. (a) Draw a well-labelled diagram of an antibody molecule.
(b) Which type of antibody is produced during allergic reaction?
Answer : (a) The labelled diagram of an antibody molecule is as follows:  

(b) IgE type of antibody is produced during allergic reaction.

SECTION – D

31. (a) What is the significance of a test cross in cross breeding experiments?
(b) A child has blood group ‘O’. If father has blood group ‘A’ and mother has blood group ‘B’, work out the genotypes of the parents and the possible genotypes of the other offsprings.
Answer : (a) Crossing of F1 individuals having dominant phenotype with its homozygous recessive parent is called test cross. The test cross is used to determine whether the individuals exhibiting dominant character is homozygous or heterozygous. For example, when a tall plant is crossed with dwarf plant, only tall plants appear in F1 generation. F1 tall plant is then crossed with homozygous recessive (tt) parent in a test cross as shown below. 

(b) If the father has blood group ‘A’ i.e., IAIA (homozygous) and mother has blood group ‘B’ i.e.,
IBIB then all the offsprings will have blood group ‘AB’ (IAIB) and not blood group ‘O’ as shown below.  

Child will have blood group ‘O’ only when both the parents are heterozygous, i.e., father IAi and mother IBi.
Thus the genotypes of the parents of child with blood group ‘O’ will be IAi and IBi. There is possibility of 3 other types of genotypes in offsprings. They are IAi (blood group A), IBi (blood group B) and IAlB (blood group AB).

OR

(a) Who proposed the chromosomal theory of inheritance? State its salient features.
(b) What would be the inheritance pattern in F1 generation for a dihybrid cross between two heterozygous parents, with the two loci of their gene pairs closely linked?
Answer : (a) Sutton and Boveri proposed chromosomal theory of inheritance in 1902. The salient features of this theory are :
(i) Chromosomes are vehicles of hereditary information and possess mendelian factors or genes.
(ii) It is the chromosomes, which segregate and assort independently, during transmission from one generation to the next.
(b) If two loci are linked (i.e. alleles are located closely on the same locus of a chromosome), there would be no segregation (assortment) of alleles or traits due to complete linkage. Therefore, the distribution of phenotypic features in F1 generation will be similar to that of the parents. The law of independent assortment, involving inheritance of two traits together, occurs only under two conditions :
(i) When genes of different traits are located on different chromosomes.
(ii) If genes of different traits are located on the same chromosome, they must be located distantly to allow crossing over.

32. Refer to the following figures of embryo implantation and answer the following questions. 

(i) Identify the structure P, Q, R, S and A.
(ii) Explain the embryonic disc with the help of given figure. Which cells in structure S give rise to it?
(iii) Describe the phenomenon of implantation in brief.
Answer : (i) P – Trophoblast, Q-Uterine epithelium, R – Blastocoel, S – Inner cell mass, A – Amniotic cavity
(ii) The cells of inner cell mass gets differentiated into two layers around 8 days after fertilisation, i.e., C-hypoblast (primitive endoderm) and B-epiblast (primitive ectoderm). The cells of these two layers form a two layered embryonic disc. The inner cell mass has stem cells which have the potential to form all tissues and organs. These stem cells give rise to embryonic disc. (iii) Implantation is anchoring or embedding of the blastocyst into endometrium of uterus. It begins about seventh day after fertilisation of ovum (generally between 6th and 9th days after fertilisation). It takes about three days for the process to be completed. The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and an inner group of cells attached to trophoblast called the inner cell mass. The trophoblast layer then gets attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment, the uterine cells divide rapidly and covers the blastocyst. As a result, the blastocyst becomes embedded in the endometrium of the uterus. This whole phenomenon is called implantation and it leads to pregnancy.

OR

Given figure shows the special adaptation in a flower for pollination. 

(i) Identify the structure P, Q and R. Recognise the type of flower based on contrivance present in it.
(ii) What is structure S? Describe its role.
(iii) Name the mechanism and its purpose to occur in the flower. Also, name the plant in which it occurs.
Answer : (i) The structures P, Q and R in the flower A are closed stigma, sterile anther lobe and fertile anther lobe, respectively. The given flower is protandrous flower with bilobed corolla.
(ii) The structure S is stigma of flower B. It receives pollen grain from the back of insect that has brought the pollen grains from flower A.
(iii) The mechanism that operates in the flower is turn-pipe or lever mechanism. It operates to promote cross pollination. It occurs in Salvia.

33. Explain the role of the following in the body defenses:
(i) Antihistamine (ii) Plasma cells (iii) Helper T cells
Answer :  (i) Antihistamine is a drug that inhibits the action of histamine in the body by blocking either of two types of receptors for histamine, H1 or H2. When stimulated by histamine, H1 receptors may produce such allergic reactions as hay fever, pruritus (itching), and urticaria (nettle rash). Antihistamines that block H1 receptors (H1-receptor antagonists) are used to relieve these conditions. (ii) Plasma cells are antibody-producing cells found in blood forming tissues and also in the epithelium of the lungs and gut. They develop in the bone marrow, lymph nodes and spleen when antigens stimulate B-lymphocytes to produce the precursor cells that give rise to them. (iii) Helper T cell is a type of T-lymphocyte that plays a key role in cell-mediated immunity. They produce a growth factor that stimulates B-cell proliferation and differentiation and also stimulates antibody production by plasma cells. Helper T-cells also enhance activity of cytotoxic T-cells.

OR

(a) How can microbes be useful in production of beverages?
(b) Name a green manure crop? How does it help in increasing fertility of soil?
Answer : (a) Microbes especially yeasts, have been used from time immemorial for the production of beverages like wine, beer, whisky, brandy or rum. Yeast Saccharomyces cerevisiae used for bread-making and commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices, to produce ethanol. Depending on the type of the raw material used for fermentation and the type of processing (with or without distillation) different types of alcoholic drinks are obtained. Wine and beer are produced without distillation, whereas whisky, brandy and rum are produced by distillation of the fermented broth.
(b) A green manure crop is Crotolaria juncea. The plants are leguminous which possess root nodules where atmospheric nitrogen is fixed by Rhizobium bacteria. Therefore, these plants enrich the soil by supplying fixed nitrogen, organic matter and other nutrients.