CBSE Sample Papers for Class 12 Biology Paper 3

CBSE Sample Papers for Class 12 Biology Paper 3 are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 3.

CBSE Sample Papers for Class 12  Biology Paper 3

Board	CBSE
Class	XII
Subject	Biology
Sample Paper Set	Paper 3
Category	CBSE Sample Papers

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 3 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time: 3 Hours
Maximum Marks: 100

General Instructions:

• There are total 26 questions and five sections in the question paper. All questions are compulsory.
• Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
• Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
• Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
• Section D contains question number 23, Value Based Question of four mark.
• Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
• There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examiner is to attempt any one of the question out of the two given in the question paper with the same question number.
• No. of printed pages are three.

SECTION-A

Question 1.
What do you mean by the terms staminate and pistillate flowers? Discuss each with examples.

Question 2.
What are exotic species?

Question 3.
State the category of viruses that carries the process of reverse transcriptase. What is the purpose of this enzyme?

Question 4.
It is often said that noise level can be reduced by placing the carpets and drapes on the floor or on wall surfaces in a room. If it is true, given reason.

Question 5.
How does silencing of specific mRNA in RNA interference prevent parasitic infestation?

SECTION-B

Question 6.
Do you think that the zygote becomes dormant for sometimes in a fertilized ovule? Justify. 2

Question 7.
A female player in your locality has been banned from playing because of the absence of one X-chromosome (i.e. 45 with XO). Mention the name of such syndrome along with other sympfoms. Is this behavior really applicable?

Question 8.
Draw the sketch of a zoospore and a conidium.
OR
Mention one dissimilarity between them and two features common to both structures.

Question 9.
A environmentalist believes that if the level of dissolved oxygen of water gets dropped to zero, the water will become septic in nature. Explain giving an example of an aquatic body.

Question 10.
How do kangaroo rats live in the absence of water in North American deserts?

SECTION-C

Question 11.
What are the advantages of using biofertilisers in agriculture?

Question 12.
A policeman finds a very small piece of body tissue from the site of a crime and takes it to the forensic department.

1. By which technique will they amplify the DNA collected from the tissue sample?
2. Mention in a sequence, the three steps involved in each cycle of this technique.
3. What is the role of thermostable DNA polymerase in this technique?

Question 13.
Illustrate the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR) diagrammatically.

Question 14.
What are CFCs? Explain their contribution in ozone depletion. List out the harmful effects of ozone depletion.

Question 15.
Work out a flowchart representation of a process of fertilization in human body initiating from the discharge of semen into female’s vagina till the fusion with ovum to form a diploid zygote.

Question 16.
A mixture of fragmented DNA was electrophoresed in an agarose gel. After staining the gel with ethidium bromide, no DNA bands were observed. What could be the reason?

Question 17.
A fRNA is charged with amino acid methionine.

1. Name the process involved in the attachment.
2. Point out the mRNA codon and anticodon fRNA for this amino acid.
3. What is heterochromatin?

Question 18.
A biotechnologist while growing a recombinant bacterium in a bioreactor forgets to add an antibiotic to the medium. What is the logic behind using antibiotic in such medium? Does its adding or not adding really makes an issue? Justify.

Question 19.
When Sachin visited his doctor, he confirmed that Sachin is suffering from chicken pox. His father got stressed. Doctor said that there is nothing to get worried about because he will not have the same disease for rest of his life. Explain the reason behind doctor’s such saying.

Question 20.
Why are molecular scissors so called? Write their use inbiotechnology.

Question 21.
In what way the plants gets benefited from the mycorrhizal symbiotic association? Give any three benefits.

Question 22.
What are STDs? What are the other terms used for STDs?

SECTION-D

Question 23.
Ankita had a fight with her friend while discussing about the process of evolution. As she told her friend that evolutionary process is continuous and everything around the globe is evolving. Her friend rather argued and said that we humans are not evolving. Whom do you think is correct — Ankita, her friend or both of them? Write your views about this fact.

SECTION-E

Question 24.
1. Give a diagramatic representation of trophic level in the ecosystem.
2. Explain the following terms.
(a) Food web
(b) Trophic level
OR
(1) (a) Name the biogeochemical (nutrient) cycle shown below.

(b) Name an activity of the living organisms not depicted in the cycle by which this nutrient is returned to the atmosphere.
(2) How would the flow of nutrient in the cycle be affected due to large scale deforestation? Explain giving reasons.
(3) Describe the effect of an increased level of this nutrient in the atmosphere on our environment.

Question 25.
(1) Discuss and workout Mendel’s monohybrid cross upto F2 generation expressing an example of seed coat colour as a trait in Pisum sativum.
(2) State the law of inheritance been derived from such a cross.
(3) How is the phenotypic ratio of F₂ generation different in a dihybrid cross?
OR
(1) You are given tall pea plants with yellow seeds, whose genotypes are unknown. How would you find the genotype of these plants? Explain with the help of cross.
(2) Identity A, B and C in the table given below.

Pattern of Inheritance	Monohybrid FI Phenotypic Expression
Co-dominance	‘A’
‘B’	Progeny resembled only one of the parents
Incomplete dominance	‘C’

Question 26.
Write a detailed note on preventive measures for various disease and their importance.
OR
(1) How normal cells get transformed into cancerous neoplastic cells? Mention the difference between viral oncogenes and cellular oncogens.
(2) Write a short note on detection of cancer.

Answers

SECTION-A

Answer 1.
Staminate flowers are those which lacks pistils e.g. Cucurbits while Pistillate flowers are the one that lacks stamens, e.g., Papaya.

Answer 2.
Exotic species are those species that are not naturally found in the habitat. They are also termed as alien species. They are mostly introduced in a habitat from outside. They can become invasive too.

Answer 3.
Viruses carrying reverse transcriptase are retroviruses which have RNA as their genetic material. These viruses catalyses formation of DNA from RNA.

Answer 4.
Yes, it is true, because these materials act as sound absorbing material and therefore, can reduce the effect of both high and low pitched sounds. For greater effectiveness, these materials should even be installed as much close to the noise source as possible.

Answer 5.
Parasitic infestation can be prevented by using RNA interference (RNAi) process, which is checked by silencing of specific mRNA due to a complementary c/sRNA which binds and prevents translation of the mRNA (silencing).

SECTION-B

Answer 6.
Zygote is dormant for sometime in a fertilized ovule because it develops only after the development of an endosperm. This is an adaptation to ensure nutrition to the growing embryo.

Answer 7.
The player has Turner’s syndrome in which the females are sterile in character because their ovaries behaves as rudimentary. They also lack other secondary sexual characters. Avoiding such person and isolating her from the locality because of this chromosomal syndrome is not applicable because chromosomal disorders are not communicable in nature.

Answer 8.
The sketch of a typical zoospore and conidium are given below:

Similarity

• Both zoospore and conidium are the asexual reproductive structures.
• Both (zoospore) Chlamydomonas and (conidia) Penicillium belong to kingdom-Fungi.

Dissimilarity

Zoospores are motile asexual reproductive structure, whereas, conidia are non-motile asexual reproductive structure.

Answer 9.
Level of dissolved oxygen acts as an important measure of the health of any stream, because this oxygen which dissolves in water through the mixing of water surface with the atmosphere is been used by the fishes and another aquatic bodies and plants. If the levels fall too low, these organisms and plants fails to survive as the water becomes septic and smells rotten due to dominancy or high growth of a low oxygen sulphur bacteria in it.

Answer 10.
Kangaroo rats are capable to live in the absence of water through their internal fat oxidation in which water acts a by product. They also have the ability to concentrate their urine to a minimal volume.

SECTION-C

Answer 11.
The advantages of using biofertilisers in agriculture are:

1. Biofertilisers does not cause any pollution.
2. These are cheap and economical.
3. Some of them also act as biopesticides.
4.  In ill-irrigated conditions, few biofertilisers can enhance the crop yield.
5. They improve soil structure and functions.
6. They make vitamins and other growth promoting biochemicals available.

Answer 12.
(1) DNA fingerprinting is a very useful technique to identify criminals in the forensic laboratories.
(2) Three steps involved in the process of DNA fingerprinting are:
Step I DNA is cut into fragments with restriction enzymes into precise reproducible sequence.

Step II the separated DNA sequence are transformed on to a nitrocellulose or nylon membrane.

Step III the sequence probes target a specific nucleotides sequence that is complementary to them.
(3) Thermostable DNA polymerase [taq DNA Polymerase) is used to catalyse the reaction in order to produce many copies of the extracted DNA by the use of PCR.

Answer 13.

Answer 14.
CFCs are chlorofluorocarbons widely used as refrigerants. CFCs being discharged in the lower part of atmosphere move upward and reaches the stratospheric layer of the atmosphere. UV rays act on CFCs and releases Cl atoms which in turn degrades ozone releasing molecular oxygen and affects ozone levels.
Harmful Effects of Ozone Depletion:

1. UV-B damage DNA and may cause mutation.
2. Causes ageing of skin, damage to skin cells and various types of skin cancers.
3. In human eyes, cornea absorbs UV-B radiation and a high dose of UV-B causes inflammation of cornea called snow blindness, cataract etc.

Answer 15.

Answer 16.
DNA bands were not observed when a mixture of fragmented DNA was electrophoresed, because:

1. Concentration of agarose in the gel is not proper, as greater the concentration of agarose gel used, greater will be the facilitation of the separation of small DNA fragments. Whereas, smaller the concentration of agarose, higher will be the resolution of bands.
2.  If the concentration of salt in the buffer is not proper.
3. If the DNA sample is contaminated with RNA or any other impurity or if the concentration of DNA is too low.

Answer 17.
(1) Translation
(2) mRNA codon is AUG and anticodon on fRNA is UAC.
(3) Chromatin that is more densely packed, stains dark is called heterochromatin.

Answer 18.
Antibiotic in any medium growing recombinant bacterium acts as tool because in the absence of an antibiotic, there will be no pressure on recombinants to retain the plasmid which is eventually carrying the gene of our interest. And the high copy number of plasmid which acts as a metabolic burden will fail to get maintained.

Answer 19.
For the first time his body’s immune system exhibited primary response and the memory of chickcnpox vims will get by the immune system. Now, whenever the same vims will attack this boy, the immune system will produce an intense response, preventing the body from getting chickcnpox again. Thus, protecting the boy from getting infected by chickenpox forever in life.

Answer 20.
The restriction endonucleases are called molecular scissors as they cut the DNA segment at particular locations, g., EcoRI.
The restriction enzymes cut the DNA strands a little away from the centre of the palindromic sites but between the same two bases on the opposite strands. This leaves single stranded

portions with overhanging stretches called sticky ends on each strand as they form hydrogen bonds with their complementary cut counterparts. This stickiness at the ends facilitates the action of the enzyme DNA ligase.

Molecular scissors have help in development of Genetically modified organisms such as crops made tolerant to abiotic stresses, reduced reliance on chemical pesticides, enhanced nutritional value of food, e.g., Vitamin A enriched rice. Cry gene such as Cry IAc and cryllAb was made to control cotton bollworms and com borer respectively.

Answer 21.
Plants get benefited by the mycorrihizal association in the following ways:

• Plants become resistant to root borne pathogens
• They even become tolerant to salinity and drought
• Growth and development of the plant get increased.

Answer 22.
Sexually Transmitted Diseases (STDs) are the diseases that are mainly passed from one one person to another during the sexual contact. They are also known as veneral diseases or reproductive tract infection. The common way to prevent the transmission of STDs is to avoid unprotected sexual contact. However, some STDs like genital herpes can still be passed even if a condom is used. Early medication with the help of a doctor can give some relief.

SECTION-D

Answer 23.
Human evolution means the evolutionary process that leads to the appearance of anatomically modem humans. When we think of human evolution our minds wander back to thousands of years it took natural selection to produce the modem man day-by-day. But the question arises that are we still changing or evolving as a species, even today also.

So, it has been scientifically proved that despite modem technology and industrialization, human continued to evolve. Also it is not only that we are evolving, were doing so even faster than before. In last 10,000 years, the pace of our evolution has been speeded up to 100 times, creating more mutation. For example, human are losing their wisdom teeth, become more resistant to various diseases and brains have shrinked than before etc.

SECTION-E

Answer 24.
(1) Representation of trophic levels in the ecosystem is given below:

(2) (a) Food Webs: All organisms depend upon one or other for food and hence, forms a food chain. The naturally occurring food chains makes further the food webs.

(b) Trophic Level is a specific position of an organism based on the source of nutrition in the food chain. All organisms occupy a particular place in their natural surrounding or in a community according to their feeding relationship with other organisms.
OR
(1)
(a) The given biogeochemical cycle shown is a carbon cycle.
(b) Volcanic activity and mining or microbial decomposition of organic matter.
(2) Due to large scale deforestation, the flow of carbon in the environment will be disturbed because plants are the major consumers, which utilize carbon in the process of photosynthesis. This would lead to accumulation of carbon in the atmosphere.
(3) Increase in the level of carbon in atmosphere will result in greenhouse effect. This will lead to heating of earth’s surface and finally to global warming.

Answer 25.
(1) In monohybrid cross, when homozygous dominant and homozygous recessive parents are crossed, F₁ hybrid would be heterozygous for that trait and would express as the dominant allele.

(2) The hybrid is heterozygous containing both alternative alleles (e.g, Y and y) but only one trait, i.e., yellow colour appear and green colour trait is suppressed in F₂ This shows that yellow seed colour is dominant over the green seed colour trait. This explains Mendel’s law of dominance.
(3) Phenotypic ratio in F₂-generation : In monohybrid cross 3 : 1 In dihybrid cross -9:3:3:
OR
(1) The given tall pea plant with yellow seeds need to be crossed with a dwarf plant with green seeds. The dominant traits are tallness and yellow colour of seeds. The recessive traits are dwarfness and green colour of seeds.
Cross between tall plant/yellow seeds and dwarf plant/green seeds.

In this cross, the F₁  generation shows
Four phenotypes ratio — Tall yellow : Tall green : dwarf yellow : Dwarf green. Genotype ratio — TtYy : Ttyy : ttYy : ttyy
(2)
A – Domant trait,
B – Dominance
C – Phenotype obtained in blending of two parental trait

Answer 26.
Different diseases have a specific set of preventive measures:
(1) Preventive measures for diseases spread by contaminated food and water
(a) Measures for personal hygiene:

• Keeping body clean, cutting nails and hair regularly.
• Consumption of clean water and contamination free food, vegetables and fruits.
• Washing hands before every meal and after defecation.
• Cooking the food in clean water and keeping it at safe temperature.
• Storing raw and cooked food separately.

(b) Measure for public hygiene:

• Proper disposal of water and excreta.
• Cleaning and disinfection of pools, water tanks and other water reservoirs.
• Hygienic practice should be adopted at restaurants and hotels.

(2) Preventive measures for air borne disease:   

• Close contact with infected person should be avoided.
• Use of same towels and other articles of infection person should be avoided.
• Washing hands regularly after sneezing, coughing, etc.

(3) Preventive measures for vector borne disease:

1. Breeding places of vector should be eliminated.
2. Stagnation of water should be avoided to control the breeding of mosquitoes.
3. Use of mosquito repellents, nets and wire mesh on doors and windows.
4. Wearing protective clothes like pants and full sleeves shirts, etc.

OR

(1) The uncontrolled proliferation of cells results in clones called neoplasm or tumour. In this way a normal cell get transformed into a cancerous cell.

Viral Oncogenes: These are the viral genes, which cause cancer.

Cellular Oncogenes: These are the genes in normal cells, which cause a cell to become cancerous under certain conditions.

(2) Cancer detection is considered to be the first step towards treatment. Its early detection is essential for its cure.

Some of the ways to detect cancer are:
(1) Biopsy: A piece of the suspected tissue cut into thin sections is stained and examined under microscope.

(2) Computer Tomography: It uses X-ray to generate a three-dimensional image of the object.

(3) MRI: It uses strong magnetic fields and non-ionising radiation to accurately detect pathological changes in the living tissue.

(4) Antibodies: against cancer-specific-antigens are also used for the detection of certain cancers.

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