CBSE Sample Papers for Class 12 Biology Solved 2016 Set 3
Section A
1.It is said that process of oogenesis terminates when the oocyte changes into a Graafian follicle. Why?
2.Give examples of each of autosomal dominant and autosomal recessive Mendelian disorder found in human beings.
3.Algal blooms affect the life in water bodies. Explain how?
4.State the type of barrier of immune system with which a person is born and is always available to protect the body.
5.Kangaroo rat does not drink water but is still able to fulfill its water needs. Justify.
Section B
6.The 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 it’s quality.
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 bonyfishes.
8.Pranav and his group performed tissue culture experiment using explants in 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? Also tell how they are cultured?
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.
10.List any two ways to show that genetic modification in plants has been done to change their phenotypic expression.
Section C
11.State the reason behind using 35 S and 32 P in the experiments conducted by Hershey and Chase to establish that DNA acts as a genetic material.
12.The biogas plant shown below is used in rural areas for the production of biogas.
(i)Observe the figure and label the different parts marked.
(ii)Explain the working of a biogas plant.
Or
In what way does baculoviruses are used as the biological control agents? Mention their importance in organic farming.
13.Explain the structure of a typical microsporangium with a help of its labelled enlarged view. Also highlight the major roles played. The innermost layer of the microsporangium.
14.Give reasons for the following
(i)Parasites tend to loose certain organs.
(ii)Clownfish lives among the tentacles of sea anemone.
(iii)Desert plants bears thick cuticle on their leaf surfaces.
15.(i) State the type of technique shown in the diagram and its importance.
(ii)Identify the step occurring in the middle and its utility
(iii)Mention the role of tag polymerase in the technique.
16.Draw an outline sketch of xerarch succession occurring in an ecosystem.
17.There is more species rich biodiversity in the tropical latitude when compared to the temperate ones. Justify the statement giving two reasons.
18.Diagrammatically represent the schematic sketch of replication fork of DNA indicating the importance of different enzymes involved in it.
19.Akshay’s father often complaints 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 or method of diagnosis a person can undergo in order to detect cancer.
20.Different assisted reproductive technology has now provided the hope for many infertile couples to achieve pregnancy by artificial means. Explain any three of them.
21.Basis of Darwin’s theory of natural selection explains about the appearance of new forms of life on earth. Justify the statement.
22.Biodiversity is important to mankind in both cultural and religious way. Justify the statement.
Section D
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 a 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
24.(i) Draw a schematic labelled diagram of the development of an embryo sac of an angiosperm plant.
(ii) Describe only with the help of diagram, the stages of development of an embryo in a dicot plant.
Or
(i)Draw a diagrammatic sectional view of human ovary showing different stages of oogenesis along with a corpus luteum.
(ii)Where does morula forms in human female? Also explain the process of its development from zygote.
25.Amit had a business of supplying the milk of cattles in home. He was disturbed with his financial conditions and was not in a condition to buy a new cattle. One of his friend 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
(i)Mention the process how does the activated sludge get produced during sewage treatment.
(ii)Explain the process of production of biogas with this activated sludge with the importance of the biogas so produced in a daily life.
26.(i) Describe the important characteristics a cloning vector must possess.
(ii) State the reason behind a fact that why 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
(i)Cutting the desired gene at specific location.
(ii)Synthesis of multiple copies of this desired gene mentioning all steps required.
Section A
1.It is said that process of oogenesis terminates when the oocyte changes into a Graafian follicle. Why?
Ans. The process of oogenesis in human females begins with the formation of primary oocytes at puberty and terminates at the time of menopause.
2.Give examples of each of autosomal dominant and autosomal recessive Mendelian disorder found in human beings.
Ans. (i) Autosomal dominant – Myotoxic dystrophy
(ii)Autosomal recessive – Sickle-cell anaemia
3.Algal blooms affect the life in water bodies. Explain how?
Ans. Algal blooms pollutes water and deteriorates its quality by depleting the oxygen content due to which the water becomes toxic.
4.State the type of barrier of immune system with which a person is born and is always available to protect the body.
Ans. The type of barriers of innate immune system are
(i)Physical barrier (ii) Physiological barrier
(iii)Cellular barrier (iv) Cytokine barrier
5.Kangaroo rat does not drink water but is still able to fulfil its water needs. Justify.
Ans. Kangaroo rat is able to fulfil its water needs from the food it eats.
Section B
6.The 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 it’s quality.
Ans. Farmer should apply a biofertiliser to his crops as biofertiliser contains living organisms which is when applied to the plants or soil promotes the growth of the crops without harming the nutrient quality of the plant.
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 bonyfishes.
Ans. 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. This is mediated by the chemical components of pollen interacting with those of the pistil.
Or
Sexual reproduction of frogs and bonyfishes has two main characteristics
(i)Both of these releases mature gametes simultaneously.
(ii)Both of them enhance the chances of syngamy (external fertilisation) by releasing a large number of gametes in water.
8.Pranav and his group performed tissue culture experiment using explants in 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? Also tell how they are cultured?
Ans. The explant is grown in a petridish/test-tube under sterile conditions in a special nutrient medium which must contain sugar, 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 tissue culture) are genetically identical to the original plant from where they are cultured, hence they are called somaclones.
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.
Ans. Two ways in which these differences and similarities can be determined are either analogy or homology.
(i)Analogy In this, organs are functionally similar, but are anatomically different.
(ii)Homology In this, organs are structurally similar, but are functionally different.
10.List any two ways to show that genetic modification in plants has been done to change their phenotypic expression.
Ans. Genetic modification of plants has been done to change the following phenotypic expression of the plants by the following two ways
(i)By reducing the dependence on chemical pesticides, i.e. pest resistant plants has been produced.
(ii)By increasing the efficiency of mineral usage in plants and preventing the early exhaustion of the fertility of the soil.
Section C
11.State the reason behind using 35 S and 32 P in the experiments conducted by Hershey and Chase to establish that DNA acts as a genetic material.
Ans. 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, viruses 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.
12.The biogas plant shown below is used in rural areas for the production of biogas.
(i)Observe the figure and label the different parts marked.
(ii)Explain the working of a biogas plant.
Or
In what way does baculoviruses are used as the biological control agents? Mention their importance in organic farming.
Ans. (i) Different parts marked are A – Sludge tank, B – Gas holder, C- Charge Pit
(ii)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 rising as the gas is produced in the tank due to the microbial activity of methanogens like
Methanogens grows anaerobically on cellulose present in a cow dung producing large amount of methane(CH4), hydrogen( H2)and carbon dioxide(C02). 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 biological control agents 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.
Importance in Organic Farming It is desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme. In organic farming, baculoviruses are also used when an ecologically sensitive area is being treated in order to kill harmful insects and to conserve the beneficial ones. (1)
13.Explain the structure of a typical microsporangium with a help of its labelled enlarged view. Also highlight the major roles played. The innermost layer of the microsporangium.
Ans. Microsporangium or pollen sac is a sporangium that produces numerous spores, which further gives rise to a male gametophyte. Each microspore germinates and is known as 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. Which performs a number of functions in a microsporangium.
(i)Nourishment of the developing microspore mother cells and pollen grains.
(ii)Production of lipid rich ubisch granules.
(iii)Secretion of enzymes like callase which is responsible for the degradation of callose wall around pollen tetrad.
14.Give reasons for the following
(i)Parasites tend to loose certain organs.
(ii)Clownfish lives among the tentacles of sea anemone.
(iii)Desert plants bears thick cuticle on their leaf surfaces.
Ans. (i) Because they obtain simple and digested food from the host, therefore, they have reduced ingesting and egesting organs.
(ii)The interaction between a clownfish and a sea anemone is called commensalism. As the sea anemone has stinging tentacles, the clownfish gets protection from its predators which keeps them away from the stinging tentacles of the sea anemone. Thus, the clown fish is benefitted while on the other hand sea anemone is neither benefitted nor harmed.
(iii)Desert plants have a thick cuticle on their leaf surfaces and have their stomata arranged in deep pits to minimise the water loss through transpiration. These plants have special photosynthetic pathway (CAM) that enables their stomata to remain closed during day time and to minimise the rate of transpiration in them.
15.(i) State the type of technique shown in the diagram and its importance.
(ii)Identify the step occurring in the middle and its utility
(iii)Mention the role of tag polymerase in the technique.
Ans. (i) The type of technique shown above is Polymerase Chain Reaction (PCR), which is used in Recombinant DNA Technology (RDT) and various other fields to amplify a small amount of DNA.
(ii)The second or the middle step occurring in the PCR is annealing (primer extension), in which two small oligonucleotide primers are used to anneal or hybridise the complementary DNA strands.
(iii)Taq polymerase is the Termostable enzyme being used in the reaction because it can tolerate the high temperature in the reaction extending the primers by adding nucleotides complimentary of the template.
16.Draw an outline sketch of xerarch succession occurring in an ecosystem.
Ans. Xerarch succession takes place in dry areas and the series progresses from xeric to mesic conditions. Finally, the climax community remains stable as long as the environment remains unchanged.
The stage of xerarch succession undergoes in a following way:
17.There is more species rich biodiversity in the tropical latitude when compared to the temperate ones. Justify the statement giving two reasons.
Ans. The reasons behind the fact is that
(i)Tropical environments are less seasonal, more constant and predictable than the temperate ones. Due to this, constant environment promotes niche specialisation and leads to a greater species biodiversity.
(ii)The availability of solar energy is much more in the tropics contributing to the higher productivity which finally in turn contributes to the greater diversity.
18.Diagrammatically represent the schematic sketch of replication fork of DNA indicating the importance of different enzymes involved in it.
Ans. The two strands of DNA cannot be separated in its entire length, so the replication occur within a small opening to the DNA helix, referred to as replication fork
DNA replication requires a set of different enzymes
(i)DNA dependent DNA polymerase It is a main enzyme which uses a DNA template (parental strands) to catalyse the polymerisation of deoxyribonucleotides.
(ii)DNA helicase It helps to unwind the DNA strand for the formation of a replication fork.
(iii)DNA ligase It facilitates the joining of discontinuously synthesised DNA fragments obtained after polymerisation.
19.Akshay’s father often complaints 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 or method of diagnosis a person can undergo in order to detect cancer.
Ans. Cancer can be easily detected by the following main methods
(i)Biopsy of a piece of suspended tissue by cutting then sections, staining and examining them under the microscope.
(ii)Blood and Bone marrow tests to know number of cell counts.
(iii)Radiography by X-rays to detect the internal organs.
(iv)Resonance imaging to detect the pathological and physiological changes in living tissue.
(v)Monoclonal antibodies against cancer specific antigens to detect cancer.
(vi)Computed tomography using X-rays used to generate 3-D image of the internal tissue.
20.Different assisted reproductive technology has now provided the hope for many infertile couples to achieve pregnancy by artificial means. Explain any three of them.
Ans. (i) GIFT (Gamete Intra Fallopian Transfer) This is a common method to treat many infertility cases. In this technique, 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.
(ii)ICSI (Intra Cytoplasmic Sperm Injection) When 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 is transferred into the Fallopian tube of the female for further development.
(iii)AIT (Artificial Insemination Technique) In this technique, the semen is collected either from the husband or a healthy donor and is artificially introduced into the vagina or into the uterus of the female. It is commonly used in cases where male partners are unable to inseminate the female due to very low sperm counts in the ejaculates.
21.Basis of Darwin’s theory of natural selection explains about the appearance of new forms of life on earth. Justify the statement.
Ans. Darwin’s theory of natural selection states the struggle for existence, i.e. the individual which have more favourable variations will enjoy a competitive advantage over which have less favourable or unfavourable variations.
In other words, only 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. Any variation, be it physical, physiological or the behavioural, which gives an individual a survival advantage over another, will acts as a selective advantage in the struggle for existence.
In this way, 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.
22.Biodiversity is important to mankind in both cultural and religious way. Justify the statement.
Ans. 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 as a representative Lord Hanuman.
Section D
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 a 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.
Ans. Richa will try to convince her family by explaining them about the phenomenon of sex determination in human beings in which male possesses oneXand 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 in each time a female becomes pregnant.
Section E
24.(i) Draw a schematic labelled diagram of the development of an embryo sac of an angiosperm plant.
(ii) Describe only with the help of diagram, the stages of development of an embryo in a dicot plant.
Or
(i)Draw a diagrammatic sectional view of human ovary showing different stages of oogenesis along with a corpus luteum.
(ii)Where does morula forms in human female? Also explain the process of its development from zygote.
(ii) Morula is formed in the upper portion of an oviduct, i.e. isthmus. The haploid nucleus of the sperm and that of the ovum fuses together to form a diploid zygote which rapidly moves through the isthmus of the oviduct by mitotic division called cleavage. As a result of which 2, 4, 8, 16 daughter cells are produced known as blastomeres. This embryo with 8-16 blastomeres is called morula.
25.Amit had a business of supplying the milk of cattles in home. He was disturbed with his financial conditions and was not in a condition to buy a new cattle. One of his friend 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
(i)Mention the process how does the activated sludge get produced during sewage treatment.
(ii)Explain the process of production of biogas with this activated sludge with the importance of the biogas so produced in a daily life.
Ans. MOET or Multiple Ovulation Embryo Transfer technology is the technique commonly used to improve the herd, 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.
(i)A cow is allowed to administered with a hormone such as follicle stimulating hormone (FSH) inducing the maturation of follicles and the process of ovulation, i.e. production of 6-8 ova per cycle
(ii)The cow is then allowed to mate with the selected bull or is artificially inseminated.
(iii)The fertilised egg at 8-32 stages are recovered and transferred to the surrogate mother.
(iv)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
(i)Activated sludge during the sewage treatment is produced 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 and is then passed into a settling tank where the bacterial floes are allowed to sediment in orderto become an activated sludge.
(ii)After the production of activated sludge, a small part of it is allowed to pumped back into the aeration tank to serve as an inoculum. The remaining part of the sludge is pumped into large tanks, i.e. anaerobic sludge digesters in which other anaerobic bacteria are also present.
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 (C02), etc. These gases are collectively known as biogas.
Importance of biogas
(a)It is used as a source of energy to produce electricity and for the purpose of heating as well.
(b)Reduces greenhouse effect.
26.(i) Describe the important characteristics a cloning vector must possess.
(ii) State the reason behind a fact that why 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
(i)Cutting the desired gene at specific location.
(ii)Synthesis of multiple copies of this desired gene mentioning all steps required.
Ans. (i) A cloning vector must possess the following characteristics in order to force a recombinant DNA into host cells.
(a)Origin of replication (ori) It is a DNA sequence from where the process of replication begins. Thus, any piece of DNA when linked to this sequence can be made to replicate within the host cells.
(b)Selectable marker It helps in identifying or selecting the transformants and eliminating non-transformants and hence, selectively permitting only the growth of the transformants.
(c)Cloning sites These are generally required to link foreign or alien DNA with the vector.For this, the vector requires very few or single recognition sites for commonly used restriction enzymes, e.g., restriction sites in E.coii cloning vector includes Hindi III, EcoR I, BamW II, Sal I, Prul etc. (2)
(ii) DNA is present in the nucleus and not in the cytoplasm of the cell just to protect it from various enzymes found in the cytoplasm which makes it difficult to reach the cell membrane to pass through it. Also DNA is a hydrophillic molecule and cannot easily pass through the cell membrane, unlike hydrophobic molecules because in those, the cell membranes are made up of phospholipids and cholesterols making the DNA molecule impermeable.
Or
In order to identify a desired gene in an organism for some experiments, the process given below will occur in the following way.
(i)Cutting of desired gene at specific location Digestions of restriction enzymes can be performed by incubating purified DNA molecules with the restriction enzyme. This is done at some optimal condition for that specific enzyme. Agarose gel electrophoresis is used to check the progress of restriction enzyme digesion.
(ii)Synthesis of multiple copies of the desired gene This can be done by using PCR (Polymerase Chain Reaction). It is also known as replication of DNA in vitro. By using PCR amplification of gene of interest can be easily done under three main steps.
(a)Denaturation ThedsDNA 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
(b)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 and dNTP’s depending upon the length and sequence of the primers.
(c)Extension The thermostable enzyme, i.e. Taq polymerase is used 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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