CBSE Sample Papers for Class 12 Biology Paper 6

These Sample papers are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 6.

CBSE Sample Papers for Class 12  Biology Paper 6

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 6 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.
It is said that process of oogenesis terminates when the oocyte changes into a Graafian follicle. Why?

Question 2.
Give examples of each of autosomal dominant and autosomal recessive Mendelian disorder found in human beings.

Question 3.
Algal blooms affect the life in water bodies. Explain how.

Question 4.
State the type of barrier of immune system with which a person is born and is always available to protect the body.

Question 5.
Kangaroo rat does not drink water but is still able to fulfill its water needs. Justify.

SECTION-B

Question 6.
A farmer was conscious about the growth of his crops and their nutrient quality. What way would you suggest to him to have better growth of crops without harming its quality?

Question 7.
Pistil has the ability to recognise the pollen grain of the right type.How?
OR
Mention two important characteristics in the sexual reproduction of frogs and bony fishes.

Question 8.
Pranay and his group performed tissue culture experiment using explants in vitro. The plants thus, obtained as a result were all genetically identical to the parent plant. State the procedure of how they are cultured? Also tell what are these plants known to be?

Question 9.
A comparative anatomy and morphological evidence shows the similarities and differences among the organisms of today and those existed years ago. Explain the two ways in which these can be determined.

Question 10.
List any two ways to show that genetic modification in plants has been done to change their phenotypic expression.

SECTION-C

Question 11.
State the reason behind using ³⁵S and ³²P in the experiments conducted by Hershey and Chase to establish that DNA acts as a genetic material.

Question 12.

The biogas plant shown below is used in rural areas for the production of biogas.
(1) Observe the figure and label the different parts marked.
(2) Explain the working of a biogas plant.
OR
In what way are baculoviruses used as the biological control agents? Mention their importance in organic farming.

Question 13.
Explain the structure of a typical micro­sporangium with a help of its labelled enlarged view. Also highlight the major roles played by the innermost layer of the microsporangium.

Question 14.
Give reasons for the following:
(1) Parasites tend to lose certain organs.
(2) Clownfish lives among the tentacles of sea anemone.
(3) Desert plants bears thick cuticle on their leaf surfaces.

Question 15.
(1) State the type of technique shown in the diagram and its importance.

(2) Identify the step occurring in the middle and its utility.
(3) Mention the role of taq polymerase in the technique

Question 16.
Draw an outline sketch of xerarch succession occurring in an ecosystem.

Question 17.
There is more species rich biodiversity in the tropical latitude when compared to the temperate ones. Justify the statement giving two reasons.

Question 18.
Diagramatically represent the schematic sketch of replication fork of DNA indicating the importance of different enzymes involved in it.

Question 19.
Akshay’s father often complains about a regular chest pain, persistent cough, hoarseness and feeling of breathlessness. The doctor predicted that his father might be suffering from any form of a cancer and should be diagnosed as early as possible. Mention the types of method to diagnose cancer.

Question 20.
Different kinds of assisted reproductive technology has now provided the hope for many infertile couples to achieve pregnancy by artificial means. Explain any three of them.

Question 21.
On the basis of Darwin’s theory of natural selection explain the appearance of new forms of life on earth. Justify the statement.

Question 22.
Biodiversity is important to mankind in both cultural and religious way. Justify the statement.

SECTION-D

Question 23.
Richa’s father and his family members were curious to have a male child after Richa, in their family. He used to always blame her mother for giving birth to a girl child and was forcing her to undergo a test for the identification of the sex of the child. Richa’s mother always refused to do this. How do you think Richa as a bright student of biology will convince her father and her family about the criteria of sex determination in human beings. Justify the arguments of Richa and her family by mentioning the positive aspects towards the situation.

SECTION-E

Question 24.
For selection of recombinants, insertional inactivation of antibiotic marker has been superceeded by insertional inactivation of a merger gene coding for chrogenic substrate. Give reasons.
OR
(1) Draw a diagrammatic sectional view of human ovary showing different stages of oogenesis along with a corpus luteum.
(2) Where does morula form in human female? Also explain the process of its development from zygote.

Question 25.
Amit had a business of supplying the milk of cattle to different homes. He was disturbed with his financial condition and was not in a condition to buy new cattle. One of his friends advised him that he can easily increase his herd size of the desired variety by the use of MOET programme. List the different steps involved in conducting the respective programme mentioning the utility of the programme.
OR
(1) Mention the process of the production of activated sludge during sewage treatment.
(2) Explain the process of production of biogas with this activated sludge with the importance of the biogas so produced in a daily life.

Question 26.
(1) Describe the important characteristics a cloning vector must possess.
(2) State the reason behind a fact that a DNA cannot pass through the cell membrane.
OR
If a desired gene is identified in an organism for some experiments, explain the process of the following:
(1) Cutting the desired gene at specific location.
(2) Synthesis of multiple copies of this desired gene mentioning all steps required.

Answers

SECTION-A

Answer 1.
The process of oogenesis in human females begins with the formation of primary oocytes at puberty and terminates at the time of menopause.

Answer 2.
(1) Autosomal dominant – Myotonic dystrophy
(2) Autosomal recessive – Sickle-cell anaemia

Answer 3.
Algal blooms pollutes water and deteriorates its quality by depleting the oxygen content due to which the water becomes toxic.

Answer 4.
The type of barriers of innate immune system are
(1) Physical barrier
(2) Physiological barrier
(3) Cellular barrier
(4) Cytokine barrier

Answer 5.
Kangaroo rat is able to fulfill its water needs by the oxidation of internal stored fat where water is formed as a by product.

SECTION-B

Answer 6.
Farmer should apply a biofertiliser to his crops as it contains micro organisms which when applied to the plants or soil promotes the growth of the crops without harming the nutrient quality of the plant.

Answer 7.
Mediation of continuous dialogue between pollen grains and the pistil by the chemical components of the pollen and pistil interaction helps in recognition of right or wrong pollen grain. If the pollen is of wrong type, the pistil rejects the pollen by preventing pollen germination on stigma or pollen tube growth in the style.
OR
Sexual reproduction of frogs and bony fishes has two main characteristics
(1) Both of these release mature gametes simultaneously.
(2) Both of them enhance the chances of syngamy (external fertilisation) by releasing a large number of gametes in water.

Answer 8.
The explant is grown in a petridish/test-tube under sterile conditions in a special nutrient medium which must contain sucrose, inorganic salts, vitamins, minerals, amino acids, growth regulators like auxin and cytokinins, etc. The medium of the culture is replaced regularly to restore nutrients in it. As all the plants (produced by tisse culture) are genetically identical to the original plant from where they are cultured, hence they are called somaclones.

Answer 9.
Two ways in which these differences and similarities can be determined are either analogy or homology.

1. In Analogy organs are functionally similar, but are anatomically different.
2. In Homology organs are structurally similar, but are functionally different.

Answer 10.
Genetic modification of plants has been done to change the following phenotypic expression of the plants by the following two ways:

1. By reducing the dependence on chemical pesticides, i.e. pest resistant plants has been produced.
2. By increasing the efficiency of mineral usage in plants and preventing the early exhaustion of the fertility of the soil.

SECTION-C

Answer 11.
Hershey and Chase worked with viruses that infects bacteria, i.e. bacteriophages to prove that DNA is the genetic material. To prove this they grew some bacteriophages on a medium containing radioactive ³²P, while another set of viruses were grown on ³⁵S medium.Viruses grown in medium containing ³²P contained radioactive DNA but not the radioactive protein, because only DNA contains phosphorus and proteins. While, on the other hand, vimses grown in radioactive ³⁵S contained radioactive protein but not radioactive DNA because DNA does not contain sulphur. Both the radioactive virus types were allowed to infect E. Coli separately. Infected bacteria were found radioactive, indicating that DNA was the material that passed from virus to bacteria.

Answer 12.
(1) Different parts marked are A – Sludge tank, B – Gas holder, C – Charge Pit
(2) Biogas plant consists of a concrete tank (10-15 feet deep) in which the biowastes are collected and slurry of dung is fed. A floating cover is placed over the slurry which is allowed to rise as the gas is produced in the tank due to the microbial activity of methanogens. Methanogens grows anaerobically on cellulose present in cow dung producing large amount of methane (CH₄), hydrogen (H₂) and carbon dioxide (CO₂). The biogas plant has an outlet being connected to a pipe to supply biogas. The spent slurry is removed through another outlet and is used as a manure.
OR
Baculoviruses are known as the pathogens that attack insects and other arthropods. These are used as a biological control and are excellent candidates for species-specific insecticidal applications. They do not show negative impact on plants, birds and non-target insects. Therefore, they are used as biological control agents.
In organic farming it is beneficial for conserving desirable insects to aid in an overall integrated Pest Management (PM) programme. They are also used when an ecologically sensitive area is being treated to kill harmful insects and conserve the beneficial ones

Answer 13.

Microsporangium or pollen sac is a sporangium that produces numerous spores, which further give rise to a male gametophyte. Each microspore germinates to a pollen grain. Microsporangium is made up of four different layers, i.e. epidermis, also known as common anther covering, endothecium, 1 -3 middle layers and an innermost layer called tapetum.
Major role played by the tapetum are:

1. Nourishment of the developing microspore mother cells and pollen grains.
2. Production of lipid rich ubisch granules.
3. Secretion of enzymes like callase which is responsiblefor the degradation of callose wall around pollen ,Enlarged view of one microsporangium tetrad.

Answer 14.

1. Parasites have reduced ingestion and egesting organs as they obtain simple and digested food from the host.
2. Sea anemone has stinging tentacles which protects the clownfish from its predators. Thus clownfish is benefited while anemone is neither harmed nor benefited. This shows commensalism interaction between the two.
3. To prevent loss of water through transpiration during the day. Even their stomata are closed with the help of photosynthetic pathway (CAM) to reduce rate of transpiration.

Answer 15.

1. The type of technique shown above is Polymerase Chain Reaction (PCR). It is used in.
   Recombinant DNA Technology (RDT) and in various other fields to amplify a small amount of DNA.
2. The middle step occurring in the PCR is annealing where two small oligonucleotide primers are used to anneal or hybridise the complementary DNA strands.
3. Taq polymerase is the Thermostable enzyme which has an ability to tolerate the high- temperature in the reaction to induce denaturation of double stranded DNA.

Answer 16.
Xerarch succession takes place in dry areas and the series progresses from xeric to mcsic conditions. Finally, the climax community remains stable as long as the environment remains unchanged.
The stage of xerarch succession undergoes in a following way:

Primary Succesion starts on the bare rock with invasion of pioneer species

↓

Lichens by secreting acids help in weathering and soil formation

↓

Bryophytes, small plants emerged out which are able to take hold in small amount of soil

↓

These arc succeeded by bigger plants/trecs in different stages as reed-swamps, submerged plants, March meadow, scrub & forest, respectively

↓

Climax forest community is achieved which remains stable till environment remain same.

↓

Xerophytic habitat gets converted to mesophytic one over a span of time

Answer 17.
The reasons behind the fact is that:
(1) As tropical environments are less seasonal, more constant and predictable they promote niche specialisation at constant environment and leads to a greater species biodiversity.
(2) Tropics has good availability of solar energy contributing to the higher productivity which finally in turn contributes to the greater diversity.

Answer 18.

Importance of different enzymes required in DNA replication are:
(1) DNA polymerase: It is a main enzyme which is highly efficient to catalyse the polymerisation of deoxyribonucleotides in a short span of time.

(2) DNA ligase: It helps in joining the discon- tinously synthesised fragments of strand with polarity
5′ → 3′ after polymerisation.

(3) DNAhelicas: It facilitates unwinding of DNA strands for replication.

Answer 19.
Main methods to detect cancer are:

1. Biopsy and histopathological study of tissue and blood.
2. Bone marrow tests for leukemia.
3. Radiography used to detect the cancer of internal organs.
4. Magnetic Resonance Imaging (MRI) to detect the pathological and physiological changes in living tissue.
5. Use of Monoclonal antibodies to detect cancer-specific antigens.
6. Computed tomography to generate 3-D image of the internal tissue.
7. Technique of molecular biology to detect inherited susceptibility of cancer.

Answer 20.
(1) GIFT (Gamete Intra Fallopian Transfer): helps in treatment of infertility cases where an ovum from the donor female is introduced into the Fallopian tube of the female who cannot produce ova but can provide suitable environment for fertilisation. Such women accept sperms from her husband during copulation.

(2) CSI (Intra Cytoplasmic Sperm Injection): First a sperm is carefully injected directly into the center of the ovum placed in a nutrient medium in the laboratory using micro needle. The early embryo so formed is transferred into the Fallopian tube of the female for further development.

(3) AIT (Artificial Insemination Technique): It is commonly used in cases where male partners are unable to inseminate the female due to very low sperm counts in the ejaculation. This technique, first collects the semen either from the husband or a healthy donor and is artificially introduced into the vagina or the uterus of the female.

Answer 21.
According to Darwin’s theory of natural selection the organism which are well adapted to their environment are fit to survive in the struggle for existence. The key factor in determining survival is adaptation to the environment, be it physical, physiological or the behavioural, gives ait individual a survival advantage over another, will act as a selective advantage in the struggle for existence.This natural selection leads to increased vigour within the species. This sorting out of the individuals with useful variations is called as natural selection by Darwin.

Answer 22.
Biodiversity is important to mankind because we obtain useful things from it but beyond the material need, it also plays a significant role in our cultural life. Hence, biodiversity acts as a source of inspiration as people admire its intrinsic beauty and it also motivates poets, writers, etc. Biodiversity gives a cultural identity in terms of festivals and rituals we have in terms of religion as well, some plants are also considered to be sacred like tulsi, peepal etc. Similarly many animals are worshipped and have religious value described in the scriptures. For example, Kaamdhenu and feeding monkeys acts as a representative of Lord Hanuman.

SECTION-D

Answer 23.
Richa will try to convince her family by explaining them about the phenomenon of sex determination in human beings in which male possesses one X and one Y chromosome while, a female has two XX-chromosomes. If an ovum fertilises with a sperm carrying X-chromosome, the zygote develops into a female (XX) while, if an ovum fertilises with sperm carrying Y-chromosome, the zygote develops into a male (XY).Hence, it shows that the genetic make up of sperm, which fertilises the ovum determines the sex of a child. Thus, it is not right to blame a mother for the birth of a girl child as it is a by chance phenomenon because there are both 50-50% chances of having either a male or a female child each time a female becomes pregnant.

 SECTION-E 

Answer 24.
Selection of recombinants due to inactivation of antibiotics is a laborious process as it requires:

•  A vector with two antibiotic resistance markers.
• Preparation of two kinds of media plates with one antibiotic each.

At first the transformed cells are plated on the antibiotic plate which has not been insertionally inactivated (say ampicillin) and kept for overnight for growth of transformants. These transformants are then replica-plated on second antibiotic (say, tetracycline) plate (which got inactivated due to insertion of gene) for selection of recombinants. The recombinants will grow only on ampicillin plate.

This whole process is laborious and time consuming as it needs two overnight incubation. On contrary, if insertional inactivation of a marker that produces colour in the presence of a chromogenic compound is chosen, then the recombinants and non-recombinants on a single medium plate can be distinguished only after overnight growth (containing one antibiotic and the chromogenic compound).
OR
(1)

(2) Morula is formed in isthmus, the upper portion of an oviduct. The diploid zygote is formed by the fusion of haploid sperm and ovum which rapidly moves by cleavage through the isthmus of the oviduct by mitotic division. As a result of which blastomeres of 2, 4, 8, 16 daugther cells are produced. This embryo with 8-16 blastomeres is called morula.

Answer 25.
MOET or Multiple Ovulation Embryo Transfer technology is the technique commonly used for herd improvement, i.e., a group of animals that live together or are kept together as a livestock.
The steps involved in the method are as follows.

1. A cow is administered with FSH for inducing the maturation of the follicles and super ovulation, i.e. production of 6-8 ova per cycle instead of one egg.
2. An administered cow is then allowed to mate with the selected bull or is artificially inseminated.
3. The fertilised egg at 8-32 stages are recovered- non-surgically and transferred to the surrogate mothers.
4. Development of embryo occurs. MOET is useful in the way that it enhances or intensify the production of genetically superior breeds of cattles and other herd animals.

OR

1. When the BOD (i.e. the amount of oxygen consumed when all organic matter in one litre of water is oxidised by the bacteria) of the effluent is reduced significantly activated sludge is produced during the sewage treatment. This is then passed into a setting tank where the bacterial floes are allowed to sediment in order to become an activated sludge.
2. A small part of activated sludge is allowed to pumped back into the aeration tank to serve as an inoculum. The remaining part of the sludge is pumped into anaerobic sludge digesters in which anaerobic microbes digests the organic mass as well as aerobic microbes (bacteria and fungi) of the sludge which in turn produces gases like methane, hydrogen sulphide (H₂S), carbon dioxide (CO₂), etc. These gases so formed are collectively known as biogas.

Importance of biogas
1. It is used as a source of energy for cooking and for the purpose of heating as well.
2. Reduces greenhouse effect.

Answer 26.
(1) To force a recombinant DNA into host cells, a cloning vector must possess the following characteristics:
(a) (Origin of replication (ori): The process of replication begins from here where any piece of DNA when linked to this sequence is made to replicate within the host cells.

(b) Selectable marker: It selectively permits only the growth of the transformants by identifying or selecting the transformants and eliminating non-transformants.

(c) Cloning sites: These are the sites which a vector requires to link a foreign or alien DNA for commonly used restriction enzyme, e.g., restriction sites in E. Coli cloning vector includes Hindi II, Ecor I, BamW II, Sal I, Prul etc.

(2)
1. The enzymes present in the cytoplasm of the cell makes it difficult for DNA to pass through and reach cell membrane.
2. Secondly cell membranes are made up of phospholipids and cholesterols which make DNA molecule impermeable being hydrophilic.
OR

1. Cutting of desired gene at specific location can be carried out by incubating purified DNA molecule with the restriction enzyme at some optimal condition. The progress of restriction enzyme digestion can be checked by Agarose gel electrophoresis.

2. Synthesis of multiple copies of the desired gene is also known as replication of DNA in vitro and can be achieved by PCR (Polymerase Chain Reaction). This involves three three main steps.

• Denaturation: The dsDNA is denatured by using high temperature of 95°C for 15 sec. Each separated ssDNA now acts as a template for the further synthesis of DNA.
• Annealing: This can be done by using two sets of oligonucleotide primers. This step is performed at somewhat lower temperature (40-60°C) using Mg²⁺ as a cofactor for Taq polymerase nd dNTPs depending upon the length and sequence of the primers.
• Extension: It is achieved by Thermostable enzyme, i.e. Taq polymerase in the reaction as it can tolerate the high amount of temperature and can extend the primers by adding nucleotides complimentary to the template.

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