Please refer to Class 12 Biology Sample Paper Set A with solutions below. The following CBSE Sample Paper for Class 12 Biology has been prepared as per the latest pattern and examination guidelines issued by CBSE. By practicing the Biology Sample Paper for Class 12 students will be able to improve their understanding of the subject and get more marks.
Section-A
Q1. Water lily is an aquatic plant, yet it shows entomophily. Why?
Answer : Water lily bears flower above the water surface hence hydrophily is not possible.
Q2. Where is acrosome present in humans? Write its function.
Answer : The anterior portion of sperm head is covered by acrosome. It contains sperm lysin to penetrate the ovum.
Q3. What is ectopic pregnancy?
Answer : Implantation of a fertilized ovum outside of the uterine cavity is called ectopic pregnancy.
Q4. Who first observed the X-chromosome? What was it called then? 1
Answer : Henking first observed the X-chromosome and he called it as X body.
Q5. Name the enzyme that joins the short pieces in the lagging strand during synthesis of DNA?
Answer : DNA ligase joins Okazaki fragments in lagging strands.
Q6. What are variable number of tandem repeats or VNTRs?
Answer : These are short nucleotide repeats in DNA that vary in number from person to person, but are inherited.
Q7. Give an example of a codon having dual function.
Answer : AUG
Q8. How do interferons protect us?
Answer : Interferon is a cytokine barrier of innate immunity which is secreted by virus infected cells and it protects non-infected cells from further infection.
Q9. Name the cry genes that control cotton bollworm and corn borer respectively.
Answer : CryIAc and cryIIAb control the cotton bollworms and cryIAb controls corn borer.
Q10. Why type II restriction enzymes are used in recombinant DNA technology? 1
Answer : Because they can be used in vitro to recognize and cut within specific DNA sequence typically consisting of 4-8 nucleotides?
Q11. Assertion (A): Insects visit flower to gather honey.
Reason (R): Attraction of flowers prevents the insects from damaging other parts of the plant.
(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.
OR
Assertion (A): Genes pass from one generation to another.
Reason (R): The unit of inheritance are genes.
(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) Honey bee visit flowers to gather nectar and turn it into honey. Visiting of insects for nectar helps in pollination.
OR
(b) Chromosomes carry gene that passes on the traits of parents to the offsprings during genetic recombination.
Q12. Assertion (A): The female external genitalia includes mons pubis, labia majora and labia minora.
Reason (R): The glandular tissue of each breast is divided into 5-10 mammary lobes.
(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)
Q13. Assertion (A): The progeny in F2-generation traits were identical to their parental type.
Reason (R): The pogeny show no blending of traits.
(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)
Q14. Assertion (A): Adenine cannot pair with cytosine.
Reason (R): Adenine and cytosine do not have a perfect match between hydrogen donor and
hydrogen acceptor sites. Hence, they cannot pair.
(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)
Read the following and answer any four questions from 15(i) to 15(v) given below:
Q15. The period between 12-18 years of age is adolescence during which child undergoes changes in his attitude and behaviour and also in biological, hormonal, structural and emotional attributes for active participation in society. These changes may lead a child on wrong path like drug addiction, alcohol abuse etc. due to mental and psychological pressure. Some of the reasons for drug and alcohol abuse include curiosity, need for adventure, excitement and experimentation.
Later, due stress of academics, to perform, impact of media, peer pressure, family problems like unstable and unsupportive family may also lead to alcohol and drug abuse.
(i) Child becomes addictive to alcohol and drugs due to
(a) associated affects of euphorbia
(b) temporary feeling of well-being
(c) stress of academics
(d) All of these
Answer : D
(ii) Due to repeated use of alcohol and drugs tolerance level of body receptor
(a) increases
(b) decreases
(c) first increases then decreases
(d) remains unaffected
Answer : A
(iii) Which of the following is not symptom of withdrawal syndrome?
(a) Nausea
(b) Sweating
(c) Sakiness
(d) Reckless behavour
Answer : D
(iv) Which is not adverse affect of drug abuse in females?
(a) Breast inlargement
(b) Deepening of voice
(c) Facial hair growth
(d) Abnormal menstrual cycle
Answer : A
(v) Assertion (A): Parents, teachers and friends should remain alert in they see any change in normal behaviour of child.
Reasons (R): Child should not be forced to performed beyond his capacity in studies, sport or other activities.
(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
Read the following and answer any four questions from 16(i) to 16(v) given below:
Q16. Bio-control agents are the living organisms which are used to control pests and disease causing
organisms. With the use of bio-control agents, the use of toxic and polluting chemicals like insecticides and pesticides have been reduced. Baculovirus are used to control insects and arthropods. Nucleopo lyhedro virus a narrow spectrum species-specific biocontrol agent is used to kill insects. There is no negative impact on plants, mammals, birds, fish etc. Only
target organisms are harmed. Sometimes bio-control agents are used along with traditional methods to control insects and pests. This is called integrated pest management (IPM).
(i) Ladybirds beetles are used to control
(a) Fungi
(b) Nematodes
(c) Aphids
(d) Termites
Answer : C
(ii) Dragonflies are used to control
(a) Butterfly
(b) Mosquitoes
(c) Crustaceans
(d) Cotton ballworm
Answer : B
(iii) Trichoderma, a fungus is used against
(a) Mosquitoes
(b) Aphids
(c) Termites
(d) Soilborne plant pathogen
Answer : D
(iv) Bacillus thuringiensis is used to control
(a) Nematodes
(b) Viral pathogens
(c) Insect pests
(d) Bacterial pathogens
Answer : C
(v) Fungi entomophaga is used against
(a) Weeds
(b) Nematodes
(c) Green peach aphid
(d) All of these
Answer : C
Section-B
Q17. How does CuT act as an effective contraceptive for human females?
Answer : CuT releases Cu ions which suppresses sperm motility and reduces the fertilising capacity of the sperms.
Q18. Why should a bisexual flower be emasculated and then bagged prior to artificial pollination in hybridisation programmes?
Answer : A bisexual flower is emasculated to prevent self pollination and then bagged to further prevent its stigma from contamination by unwanted pollen. This is all done to get the desired result in the artificial hybridisation.
Q19. How and why is the bacterium, Thermus aquaticus, useful in rDNA technology?
Answer : In PCR reaction, in the process of repeated DNA replication, the segment of DNA is amplified to approximately 1 billion time which is achieved by a thermostable DNA polymerase isolated from bacterium Thermus aquaticus.
The bacterium Thermus aquaticus (Taq) is useful in rDNA technology because it contains thermostable enzyme – DNA polymer as (Taq–DNA polymerase) which can withstand high
temperature.
Q20. Differentiate between predation and competition.
Answer : (Image 468)
OR
Cows and dogs are eurythermal animals. Why are polar bears categorised as stenothermal animals? Give one reason. (Image 468)
Answer : Polar bears tolerates narrow range of temperature so these are called stenothermal animals, while cows and dogs can tolerate and survive variety of temperature and are called eurythermal animals.
Q21. Highlight any four advantages of genetically modified or transgenic animals.
Answer : (i) Biological Products: Transgenic animals produces useful biological products only by the introduction of the portion of DNA or genes, which codes for a particular product like human protein (a-1-antitrypsin) is produced to treat emphysema.
The first transgenic cow, Rosie produced human protein-enriched milk (2.4 gms per litre).
(ii) Vaccine Safety: Transgenic mice are being used in testing the safety of vaccines before they are used on human beings.
(iii) Chemical Safety Testing: It is also called as toxicity / safety testing. Transgenic animals are developed with genes exposed to toxic substance and are used to study their effects.
(iv) Growing of Spare Parts: Spare parts (e.g., heart, pancreas) of pig for human use can be grown through the formation of transgenic animals.
Q22. What is the cross between the progeny of F1 and the homozygous recessive parent called?
How is it useful?
Answer : The cross between the progeny of F1 and the homozygous recessive parent is called test cross.
The progenies of a test cross are studied to determine the phenotype in F1 generation.
OR
Explain why it is scientifically incorrect to blame the mother for bearing female child.
Answer : Sex of a child depends on the fusion of the type of sperm (‘X’ or ‘Y’ type) with the egg. (Image 469)
Q23. What is commensalism?
Answer : Relationship between two organisms in which one organism is benefitted and there is neutral effect on another organism; is called commensalism. Many commensals live in the alimentary canal of humans to get shelter and food but they have neither positive nor negative impact on
human :
Q24. List the different types of pollination depending upon the source of pollen grain.
Answer : (i) Autogamy: Pollen grains lands on stigma of same flower.
(ii) Geitonogamy: Pollen grains lands on stigma of different flower but of same plant.
(iii) Xenogamy: Pollen grains land on stigma of different plant.
Q25. S strain → Inject into mice → ………
……… → Inject into mice → Mice live
Complete the diagram above. What was this experiment about and who performed it?
Answer : S strain → Inject into mice → Mice die
R strain → Inject into mice → Mice live
This experiment was conducted by Frederick Griffith in search of Genetic material.
Section-C
Q26. Draw a diagram of a mature embryo of grass and label six parts in it. 3
Answer : (Image 470)
Q27. Two children, A and B aged 4 and 5 years respectively visited a hospital with a similar genetic disorder. The girl a was provided enzymereplacement therapy and was advised to revisit periodically for further treatment. The girl, B was, however, given a therapy that did not require revisit for further treatment.
(a) Name the ailments the two girls were suffering from?
(b) Why did the treatment provided to girl A required repeated visits?
(c) How was the girl B cured permanently?
Answer : (a) Both the girls are suffering from adenosins deaminase (ADA) deficiency.
(b) Girl ‘A’ was provided with ‘Enzyme Replacement Therapy’ in which functional ADA is introduced into cultured lymphocytes and these lymphocytes are introduced to the patient
as lymphocytes are not immortal, and hence the patient requires periodic infusion.
(c) Girl ‘B’ was treated by bone marrow transplantation during early embryonic stage, she was treated with permanent cure.
Q28. Why are
(i) Alien species invasion and
(ii) Loss of habitat and fragmentation considered to be the major cause of loss of biodiversity?
Explain with the help of one example each. 3
Answer : (i) Nile perch when introduced into Lake Victoria in east Africa caused extinction of indigenous cichlid fish. This shows that when alien species unintentionally or deliberately
introduced in a county for any purpose, they may become invasive and become threat to indigenous species for their extinction.
ii) Destruction in habitat causes the native animals and plants to get extinct. Example: tropical rain forests are being destroyed for developing cultivable land and grasslands. Loss of an are in a forest breaks habitat into small fragments which in turn lead to loss of biodiversity.
Q29. Mention three uses of PCR in molecular diagnostics. 3
Answer : (i) PCR (Polymerase Chain Reaction) is used to detect the presence of gene sequences of the infectious agents.
(ii) It is used to detect specific microbes, from the samples of soil, sediments and water.
(iii) It is also used to detect HIV in AIDS patient.
Q30. Who proposed chromosome theory of inheritance? Point out any two similarities between the behaviour of genes and that of chromosomes.
Answer : Chromosomal theory of inheritance was proposed by Sutton and Boveri.
Both genes and chromosomes occurs in pairs. Both segregate at the time of gamete formation
such that only one of each pair is transmitted to a parent or a gamete respectively.
OR
If you are given a tall pea plant, how would you find out its genotype? Explain.
Answer :The given tall pea plant is crossed with a recessive parent or a test cross will performed. Here, the tall character is a dominant which can be homozygous (TT) or heterozygous (Tt). The offspring of the test cross will be 100% dominant, if the individual was homozygous. The ratio will be 50% dominant and 50% recessive in case of heterozygous individual. (Image 471)
Section-D
Q31. (a) What are introns and exons?
(b) Represent schematically the steps in transcription in Eukaryotes.
Answer : (a) Coding segments in DNA are known as Exons whereas non-coding segments are known as introns. (Image 472)
OR
(a) Expand BAC and YAC.
(b) What is a promoter in a transcription unit?
(c) Differentiate between template strand and coding strand.
Answer : (a) BAC stands for Bacterial Artificial Chromosome YAC stands for Yeast Artificial Chromosome
(b) A promoter initiates the process of transcription. (Image 472)
Q32. (a) What is meant by contact inhibition?
(b) Why is using tobacco in any form injurious to health? Explain.
(c) Why do sports persons often fall a victim to cocaine addiction?
Answer : (a) Contact inhibition is a property by virtue of which normal cells by contact with other cells inhibit their uncontrolled growth.
(b) Harmful effects of Tobacco are:
(i) Tobacco contains nicotine which stimulates the adrenal gland to release adrenaline and noradrenaline into blood circulation, both of which raise blood pressure and increase heart rate.
(ii) It is associated with increased incidence of cancers of lung, throat, urinary bladder,br onchitis, emphysema, gastric ulcer and coronary heart disease.
(iii) Tobacco chewing is associated with increase risk of cancer of the oral cavity.
(c) Sports person often take cocaine to increase their energy level for the game because it has a potent stimulating action to provide them instant energy. With regular intake they
fall victim to cocaine addiction as it acts on their nervous system producing a sense of euphoria and interferes with the transport of the nano-transmitter dopamine.
OR
What are flocs? State their role in effluent treatment and their ultimate fate in sewage treatment tank.
Answer : Flocs are mesh-like structures, formed due to the association of aerobic bacteria and fungal filaments.
— While growing, they consume large amount of organic matter in the effluent reducing BOD.
— The effluent is then passed into a settling tank, where the bacterial flocs are allowed to sediment for activated sludge.
— A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.
— The remaining major part of the sludge is pumped into large tanks, where the anaerobic bacteria digest the bacteria and fungi in the sludge and they produce biogas.
Q33. Why are (i) alien species invasion and (ii) loss of habitat and fragmentation considered to be the major cause of loss of biodiversity? Explain with the help of one example each.
Answer : (i) The alien species become invasive and cause a decline or extinction of indigenous species.
e.g., The Nile Perch introduced into Lake Victoria led to the extinction of more than 200 species of cichlid fish in the lake.
(ii) Habitat loss and fragmentation deprive the organisms of their natural home and hence leads to their extinction. Fragmentation of habitats, affects the mammals and birds which
require large territories and certain animals with migratory habits. e.g., When the Amazon forest is cut and cleared for conversion into grasslands, many species are affected.
OR
Biodiversity must be conserved as it plays an important role in many ecosystem services that nature provides. Explain any two services of the ecosystem.
Answer : 1. Humans derive countless direct econonic benefits from nature food like cereals, pulses, fruits, firewood, fibres, construction material, industrial products like tannins, lubricants, dyes, resins, perfumes and products of medicinal importance.
2. The fast-dwindling Amazon forest is producing 20 percent of the total oxygen, without which we cannot live for a moment. Pollination is another service, ecosystem provide
through pollinators like bees, bumblebees, birds and bats.