CBSE Class 12 Biology Sample Paper Set B

Sample Paper Class 12

See below CBSE Class 12 Biology Sample Paper Set B with solutions. We have provided CBSE Sample Papers for Class 12 Biology as per the latest paper pattern issued by CBSE for the current academic year. All sample papers provided by our Class 12 Biology teachers are with answers. You can see the sample paper given below and use them for more practice for Class 12 Biology examination.

CBSE Sample Paper for Class 12 Biology Set B


1. Give an example of a plant which came into India as a contaminant and is a cause of pollen allergy.
Answer : Parthenium or carrot grass is an example of a plant which came to India as a contaminant and is a major contributor to pollen allergy.

2. Explain the function of coleorhiza.
Answer : Coleorhiza is a protective sheath that covers the young root of the embryo in plants of the grass family.

3. Give reasons for the following :
The human testes are located outside the abdominal cavity.
Answer : The human testes are located outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2- 2.5°C) lower than the normal internal body temperature, necessary for spermatogenesis.

4. In which organism did Morgan carry out dihybrid crosses for studying genes that were sex-linked?
Answer :  Morgan carried out several dihybrid crosses in Drosophila, to study genes that were sex-linked.

5. A human being suffering from Turner’s syndrome shows monosomy. Mention the cause of this chromosomal abnormality.
Answer : Turner’s syndrome is a chromosomal disorder, which is caused due to the absence of one of the X chromosomes (XO). Thus, the number of chromosomes is 45. Such females are sterile.

6. Expand VNTR.
Answer : VNTR → Variable Number of Tandem Repeats.

7. Name an autosomal genetic disorder due to a mutation resulting in a single base pair change in DNA.
Answer : Sickle-cell anaemia is a disease that occurs as a result of point mutation.

8. What will be the consequences if a foreign gene is incorporated at Sal I site of pBR322 plasmid?
Answer : When an alien gene is ligated at Sal I site of pBR322, the gene tetr becomes non-functional and plasmid loses its tetracycline resistance. Hence, the cell possessing such recombinant pBR322 will not be able to grow on tetracycline.

9. What are recombinant therapeutics?
Answer : Therapeutic proteins produced by recombinant DNA technology are called recombinant therapeutics.

10. Why is tropical environment able to support greater species diversity?
Answer : Continuous favourable environment with little seasonal changes of temperature and moisture supports greater species diversity in tropical areas. Also, more solar energy is available in tropics, which promotes higher productivity and increased biodiversity.

11. Assertion : Tapetum helps in formation of exine layer of pollen grain.
Reason : Tapetum produces lipid rich Ubisch granules containing sporopollenin.
(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


Assertion : The coconut water is free-nuclear endosperm.
Reason : The white kernel of coconut is cellular endosperm.
(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 biolistic method, tungsten or gold particles coated with foreign DNA are bombarded into target cells at a very high velocity.
Reason : Biolistic method is also used to insert genes into animals that promote tissue repair into cells.
(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

13. Assertion : In parasite-host relationship, the stronger organism is benefitted.
Reason : Parasites are commonly prey specific.
(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 : Alpha diversity refers to species diversity present in a given community or habitat.
Reason : Alpha diversity is expressed by species richness and species evenness in a community or habitat.
(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

15. Read the following and answer any four questions from 15(i) to 15(v) given below:
A student conducted an experiment by crossing pure round yellow seeded pea plant with wrinkled green seeded pea plant. Yellow colour is dominant over green and rounded seed shape over wrinkled seed shape.
F1 plants are all round and yellow seeded. F2 generation is obtained by self-breeding F1 plants. 4 types of plants were obtained in F2 generation ; round yellow, round green, wrinkled yellow and wrinkled green.

(i) Which Mendelian law is being discussed in the given passage?
(a) Law of dominance
(b) Law of independent assortment
(c) Law of segregation
(d) All of these
Answer : B

(ii) Identify the correct statement in context of given law.
(a) Only one allele expresses itself in the hybrid.
(b) Offspring do not show parental combination of alleles.
(c) Alleles of two pairs separate independently of each other during gamete formation.
(d) This law is applicable only to closely linked genes, present on same chromosomes.
Answer : C

(iii) F2 phenotypic ratio obtained is ________ .
(a) 9 : 3 : 3 : 1
(b) 3 : 1
(c) 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
(d) 1 : 2 : 1
Answer : A

(iv) Genotype of round green seed is ________ and of wrinkled yellow is _________ .
(a) RRyy, rryy
(b) rrYy, RrYy
(c) RRyy, RrYy
(d) Rryy, rrYy
Answer : D

(v) Assertion : F2 generation shows recombinant traits.
Reason : Alleles of two different characters separate and combine independent of each other.
(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:
Living organisms are capable to cope with stressful conditions by various methods. Organisms W are able to maintain constant body temperature and constant osmotic concentration despite changes in external environment, thus have wide range of distribution. Organisms X are ectotherms, i.e., they change their body temperature with surrounding temperature. Organism X have narrow range of distribution. Organisms Y have the ability to regulate body functions to a limited extent, beyond that limit, their body temperature changes with external conditions. Organisms Z suspend development during unfavourable conditions and resume growth on return of suitable conditions.

(i) Select the correct example of organisms W, X and Z.
           W           X          Z
(a) Pigeon     Asterias    Zooplankton
(b) Dog       Zooplankton   Pigeon
(c) Zooplankton  Cow      Monkey
(d) Cow      Zooplankton  Asterias
Answer : A

(ii) Stage of suspended development is known as
(a) diapause
(b) hibernation
(c) aestivation
(d) migration.
Answer : A

(iii) Identify the organisms from given graph.

CBSE Class 12 Biology Sample Paper Set B

Answer : B

(iv) Which statement is correct for organisms X?
(a) They are very active organisms.
(b) They consume lesser amount of energy.
(c) Their body fluids have fixed osmotic concentration.
(d) All of these
Answer : B

(v) Assertion : Polar bears undergo hibernation to escape extreme cold.
Reason : Polar bears are ectothermic, thus cannot maintain constant body temperature.
(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 : C


17. Why are copper containing intrauterine devices considered an ideal contraceptive for human females?
Answer : Copper containing intrauterine devices (CuT, Cu7, etc.) are considered an effective contraceptives for human females as the Cu ions released by them suppress sperm motility and fertilising capacity of the sperms. Hence, they act as effective birth control method.


Differentiate between Leydig’s cells and Sertoli cells.
Answer : Leydig’s cells or interstitial cells are present in the spaces between adjacent seminiferous tubules and are involved in secretion of testosterone, whereas sertoli cells are present inside the seminiferous tubules and are involved in formation of sperms, providing nutrition in supporting spermatogenesis, secretion of androgen binding protein (ABP) and secretion of inhibin to check the effects of testosterone and FSH.

18. Differentiate between male and female heterogamety.
Answer : The type of sex determination mechanism shown in female XX with male XY is called male heterogamety because male produces two different types of gametes, e.g., Drosophila. The type of sex determination mechanism shown in female ZW with male ZZ is female heterogamety because female produces two different types of gametes, e.g., birds.

19. List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment.
Answer : Secondary treatment or biological treatment of sewage considerably reduces the biological oxygen demand (BOD) of primary effluent during sewage treatment. The organic matter present in the effluent is decomposed with the help of microbial flora called as sewage fungus. The effluent is constantly agitated or aerated. This causes the growth of various aerobic microorganisms and sewage fungi. These microbes digest the organic matter thereby reducing the BOD of original sewage by 10-15%.


Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatment.
Answer :  Flocs are masses of aerobic bacteria held together by slime and fungal filaments to form mesh like structures. These microbes digest a lot of organic matter converting it into microbial biomass and releasing a lot of minerals. This reduces biochemical oxygen demand or BOD. In anaerobic sludge digesters, aerobic microbes present in the sludge get killed. Anaerobic microbes digest the organic mass as well as aerobic microbes of the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas which can be used as source of energy as it is inflammable. The spent sludge of anaerobic sludge digester can be used as manure or part of compost.

20. (a) Define gene therapy.
(b) Why is recombinant human insulin better for diabetic patients than pig or cow insulin?
Answer : (a) Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child/embryo.
(b) Insulin from an animal source causes some patients to develop allergy or other types of reactions to the foreign protein, whereas recombinant human insulin is identical with human insulin.

21. (a) Name the key tools used in recombinant DNA technology.
(b) What do you mean by restriction digestion?
Answer : (a) Restriction enzymes, polymerase enzymes, ligases, vectors and the host organisms.
(b) The process of cutting DNA by restriction enzymes is called restriction digestion.

22. Which was the first transgenic cow? How did the milk obtained from this transgenic cow was different from a natural cow milk?
Answer : The first transgenic cow was Rosie. Its milk contained the human alpha-lactalbumin and was nutritionally a more balanced product for human babies than natural cow milk.

23. Name the microbes that help in production of the following products commercially :
(i) Statin (ii) Citric acid
(iii) Penicillin (iv) Butyric acid
Answer : (i) Statin – Monascus purpureus
(ii) Citric acid – Aspergillus niger, Mucor, Candida lipolytica
(iii) Penicillin – Penicillium chrysogenum, P. notatum
(iv) Butyric acid – Clostridium acetobutylicum

24. Name the parasite that causes filariasis in humans. Mention its two diagnostic symptoms. How is this disease transmitted to others?
Answer : Filariasis is a helminthic disease caused by Wuchereria (W. bancrofti and W. malayi). It causes swelling of lymphatic vessels of lower limbs resulting in swelling of feet, legs, scrotal sacs and thighs. It spreads from one human being to other through the bite of female mosquito, Culex.

25. How does offsite collection helps in conservation of biodiversity? Explain.
Answer : Offsite collections are live collections of wild and domesticated species in botanical gardens, zoological parks, wildlife safari parks and arboreta, etc. Many botanical gardens and arboreta have seed banks, tissue culture facilities and other ex-situ conservation technologies. Zoological parks have well managed captive breeding programmes due to which many animals that have become extinct in the wild continue to be maintained in zoological parks. Therefore, offsite collections can be used to conserve biodiversity.


26. Refer to the given figures and answer the following questions. 

CBSE Class 12 Biology Sample Paper Set B

(i) Which methods of birth control are shown by figure X and Y?
(ii) How do these methods provide contraception? Describe briefly.
Answer :  (i) Figure X and Y show permanent method of birth control in female and male respectively. This is called sterilisation. Sterilisation in female is called tubectomy (X) and in male it is called vasectomy (Y). (ii) In tubectomy, a small part of fallopian tube is removed or tied up through small cut in the abdomen or through vagina, while in vasectomy, a small part of vas deferens is removed or tied up through small cut on the scrotum. These methods prevent pregnancy by blocking gamete transport. Both methods are very effective but reversibility is poor.

27. What do you mean by mutation and mutagen? Write the significance of mutations.
Answer : Mutation is a phenomenon which results in alteration of DNA sequences, and consequently results in changes in the genotype, and the phenotype of an organism. In addition to recombination, mutation is another phenomenon that leads to variation in DNA. Any extracellular physical or chemical factor, which can cause mutations or increase the frequency of mutations in organisms is called mutagen. e.g. temperature and high energy radiations. Significance of mutations: (i) Mutations are the sources of all variability in a population.
(ii) Mutations have also occurred for higher milk yield, lactation period, egg production, meat content, wool yield, adaptability to diverse environments. The domestication of several plants was made possible due to sudden mutations appearing in them, e.g., stiff hairs in wheat, rice and other cereals, lint in cotton, etc.

28. Who invented polymerase chain reaction (PCR)? Explain its working procedure.
Answer : The polymerase chain reaction (PCR) was invented by Kary Mullis in 1985. The working procedure of PCR is given as : A single PCR amplification cycle involves three basic steps; denaturation, annealing and extension (polymerisation). (i) Denaturation : In this step, the target DNA is heated to a high temperature (usually 94° to 96°C), resulting in the separation of the two strands. Each single strand of the target DNA then acts as a template for DNA synthesis. (ii) Annealing : In this step, the two oligonucleotide primers hybridise to each of the single stranded template DNA since the sequence of the primers is complementary to the 3’ ends of the template DNA. This step is carried out at a lower temperature (usually 40° to 60°C) depending on the length and sequence of the primers. (iii) Extension : The final step is extension, wherein Taq DNA polymerase (obtained from Thermus aquaticus) synthesises the DNA region between the primers, using DNTPs (deoxynucleoside triphosphate) and Mg2+. It means the primers are extended towards each other so that the DNA segment lying between the two primers is copied. The optimum temperature for this polymerisation step is 72°C.


(a) What are cloning vectors. What is their function?
(b) State the role of DNA ligase in biotechnology.
Answer : (a) Cloning vectors are those organisms or their DNAs which can multiply independently of the host DNA and increase their copy number along with the foreign DNA attached to them. Cloning vectors may be plasmids, bacteriophages, cosmids, viruses, etc. Functions : (i) They help in linking the foreign DNA with that of the host. (ii) They also help in the selection of recombinants from the non-recombinants. (b) DNA ligase joins two individual fragments of DNA by the formation of phosphodiester bond between them.

29. Refer to the given flow chart and answer the following questions. 

CBSE Class 12 Biology Sample Paper Set B

(i) Identify the missing parts A and B.
(ii) What is the optimum temperature at which the above mentioned process occur and the role of bacteria in the process?
Answer : (i) A – Lactic acid; B – Vitamin B12 (ii) Indian curd is prepared by inoculating skimmed and cream milk with Lactobacillus acidophilus at a temperature of about 40°C or less. Lactic acid bacteria (LAB) like Lactobacillus are added to milk. It converts lactose sugar of milk into lactic acid. Lactic acid causes coagulation and partial digestion of milk protein casein and milk is then converted into curd, yoghurt or cheese using different processes.

30. The given table shows population interactions. Study the table and answer the following questions: 

CBSE Class 12 Biology Sample Paper Set B

Answer : (i) (P) = Amensalism (Q) = Parasitism (R) = Competition (S) = Mutualism (ii) Parasitism : It is an association between organisms of different species in which one organism (the parasite) lives on or in the body of another organism (host), from which it obtains its nutrients. It is one sided relationship in which parasite is benefitted and host is harmed. Competition : It is a rivalry between two or more organisms for obtaining the same resources. It may be between individuals of same species (intraspecific) or of different species (interspecific).


31. (a) Ramesh, a rickshaw puller is in the habit of chewing tobacco throughout the day. Since a few days, he has not been able to eat his food, as there are many ulcers in his mouth, and he is also suffering from high blood pressure. What may be the possible reason for this?
(b) How does morphine, an opioid drug affect the human body?
Answer : (a) Chewing tobacco throughout the day is affecting Ramesh’s health day by day, because tobacco contains a large number of harmful chemical substances including nicotine, an alkaloid. Nicotine stimulates adrenal gland to release adrenaline and nor-adrenaline into blood circulation, both of which raise blood pressure and increase heart rate. Tobacco chewing is associated with increased risk of cancer of the oral cavity, and that is the reason for Ramesh’s mouth ulcers. (b) Morphine is the active principle alkaloid of opium, that causes addiction. It depresses respiratory centre, leads to the fall in blood pressure and causes bradycardia (slow heartbeat). Morphine also causes release of ADH, reduces urine output, causes constipation and also mild hyperglycemia. However, morphine is a very effective sedative and painkiller.


(a) What happens to a normal cell in a body when oncogenes are activated under certain conditions?
(b) Which techniques are useful to detect cancer of internal organs?
(c) Why are cancer patients often given a-interferon during their treatment?
Answer : (a) When cellular oncogenes or proto-oncogens are activated under certain conditions in normal cells in a body, they could lead to oncogenic transformation of the cells. Transformation of normal cells into cancerous neoplastic cells may be induced by physical, chemical or biological agents also. (b) Techniques like radiography (use of X-rays), CT (computed tomography) and MRI (magnetic resonance imaging) are very useful to detect cancers of the internal organs. Computed tomography uses X-rays to generate a three-dimensional image of the internals of an object. MRI uses strong magnetic fields and non-ionising radiations to accurately detect pathological and physiological changes in the living tissue. (c) Cancer patients are often given a-interferon during their treatment, because these biological response modifiers activate the immune system and help in destroying the tumour.

32. Given graph shows the concentration of pituitary hormones and ovarian hormones during menstrual cycle.
Study this graph and answer the following questions based on it. 

CBSE Class 12 Biology Sample Paper Set B

(i) Which hormones are represented by A, B, C and D?
(ii) State the events that occur due to peak level of B and C.
(iii) Why the level of hormone D increases after ovulation?
(iv) Which phase is caused by increased production of B and D?
Answer :  (i) A – Follicle stimulating hormone (FSH), B – Estrogen, C – Luteinising hormone (LH), D – Progesterone
(ii) High concentration of estrogen (B) in blood plasma stimulates the proliferation of the uterine endometrium along with increase of uterine glands and blood vessels. High concentration of LH (C) induces rupturing of Graafian follicle and ovulation (release of ovum) occurs. (iii) After ovulation, the remaining cells of ovarian follicles develop into corpus luteum under the influence of LH. This corpus luteum secretes large amount of hormone progesterone (D) hence, its level increases after ovulation. (iv) Proliferative and secretory phase is caused by increased production of B and D. 


Refer to the given figure showing T.S. of an anther and answer the following questions.  

CBSE Class 12 Biology Sample Paper Set B

(i) Identify the structures K and L.
(ii) Give the functions of K and L.
(iii) Identify the structure M and describe its role in microsporogenesis.
Answer :  (i) K in the figure represents endothecium while L represents tapetum. (ii) The function of endothecium (K) is : 1. to protect the young anther 2. help in dehiscence of ripe anther. On the other hand, tapetum (L) has a number of functions: 1. nourishment of the developing microspore mother cells and microspores, 2. secretion of enzymes for degradation of callose wall around pollen tetrad, 3. production of Ubisch granules and pollenkitt, etc. 4. amoeboid tapetum contributes in the formation of exine. (iii) The structure M in the figure represents sporogenous cells. The sporogenous cells divide to increase their number with the growth of anther and ultimately get transformed into microspore mother cells, which further undergo meiosis to produce microspores. This process is called microsporogenesis.

33. What is an operon? Names its types. In a culture of E.coli, what happens when lactose is added? Why does the lac-operon switch off after sometime again?
Answer : An operon is a part of genetic material (or DNA), which acts as a single regulated unit having one or more structural genes, an operator gene, a promotor gene, a regulator gene, a repressor and an inducer or corepressor (from external source). Operons are of two types : Inducible and repressible. Inducible operon is an operon, which remains switched off normally, but becomes operational in the presence of an inducer (a chemical substance or substrate) e.g. lactose as in the case of lac operon. In the culture medium of E.coli, when lactose was added, Lac operon is switched on, as lactose acts as inducer, and inactivates the repressor. Due to this switching on of the lac operon system, b-galactosidase is formed, which converts lactose into glucose and galactose. As soon as the lactose is consumed, the repressor again becomes active and causes switching off, of the system.


(a) Describe aminoacylation of tRNA.
Identify the specific process in which it occurs – transcription or translation.
(b) Elaborate the steps of translation.
Answer : (a) Aminoacylation or charging of tRNA occurs during translation. In this process, a tRNA is specially linked to an amino acid. Charging is a two-step process : In the first step, an amino acid reacts with ATP, in the presence of a specific aminoacyl tRNA synthetase, to produce the activated form or an aminoacyl adenylic acid.
(b) Translation is the process in which the genetic message, carried by mRNA from the DNA, is converted in the form of a polypeptide chain, having a specific sequence of amino acids. Besides mRNA, the three key players in this process are – ribosomes, tRNA and amino acids. Translation occurs in the cytoplasm where the ribosomes are located. The main steps of translation are: (i) Initiation : For initiation, the ribosome binds to the mRNA at the start codon (AUG), that is recognised only by the initiator tRNA. (ii) Elongation : During this stage, complexes composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA, by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one and peptide bonds are established between the adjacent amino acids. This results in polypeptide sequences dictated by DNA and represented by mRNA. (iii) Termination : At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.