CBSE Sample Papers for Class 12 Biology Solved 2016 Set 1

                                                               Section A

1.Cross hybridisation among the selected parents during any plant breeding programme is meant to be a tedious and a time consuming process. Why?

2.In which phenomenon, a phenotype of the Fj hybrid offspring does not  resemble any of the parent and is intermediate between the expression of two alleles?

3.It is often seen that replication of DNA does not initiate randomly anywhere in DNA, it instead begins at definite regions. Why is it so? Give reason.

4.List two advantages of inbreeding in animals.

5.Production of antibiotics has been widespread by the pioneering efforts of which two scientists.

                                                        Section B

6.How is diapause different from hibernation?

7.What are the two major aims and objectives behind the reproductive child health care programmes?
Or
Human Placenta acts as a structural and functional unit between a foetus and maternal body. Justify the statement giving any two basic function it performs.

8.In what way does the cell mediated system works in a body when it gets infected?

9.Both linear DNA and plasmid DNA of same length having one site for a restriction endonuclease are cut and separated on agarose gel electrophoresis. The plasmid DNA shows one DNA band, while a linear DNA shows two fragments. State the reason behind the fact.

10.Mention two functions of DNA polymerase.

                                                              Section C

11.Draw a neat and well labelled diagram showing the reproductive system in human females.

12.Indian government had taken several measures to control the vehicular air pollution in Delhi and other cities of India. Enlist any three of them.

13.Amoebiasis is often caused by an intestinal parasite which being found in the large intestine of human beings. Give the name of the organism responsible for this. Also write the symptoms and mode of transmission responsible for the disease.

14.Enlist the main differences between the two types of nucleic acids found in living systems.
Or
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-2
(i) Identity the molecule X’ synthesised by ‘i’ gene. How does this molecule get inactivated?
(ii) Identity the structural genes that codes for {3-galactosidase.
(iii) When does the transcription of this gene gets stopped?

15.Expand the term GMOs. Also explain the fact in what form a GMO differs from a hybrid?

16.By taking an example of some of Australian marsupials and Australian placental mammals, briefly explain the phenomenon of adaptive radiation and convergent evolution in different species.

17.It is merely important to test a new plant variety in a systematic way during different plant breeding programmes in a geographically vast country like India Justify.

18.(i) List any two conditions on which the development of a diploid cell depends.
(ii) If the number of chromosomes present in the meiocyte of a plant is 24, then
work out the number of chromosomes in the gamete, zygote and embryo of this plant.

19.On a visit to a food processing industry, students saw that workers were working in a huge tank size vessels. Teacher explained them that these vessels are used for the process of fermentation.

(i) Write about the process of fermentation and how it takes place.

(ii) List some important applications of microbes in different industries.

20.Biotechnologists identified the source and isolated different types of cry genes from the bacterium Bacillus thuringiensis and incorporated that into many crops. Briefly explain, how have these genes brought beneficial changes in the genetically modified crops and to the mankind?

21.The diagrammatic illustration of connection between the different trophic levels is given below
(i) Identify the type of ecological pyramid given below and explain what does the base and the apex of this pyramid is indicating.
(ii) Give examples of such types of ecological pyramids with respect to number and biomass.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-4

22.Branching descent and natural selection acts as two main key concepts of Darwinian theory of evolution. Discuss each concept with the help of a suitable example.

                                                       Section D

23.Neeta Class Xth student was selected by her teacher for the debate competition to represent her school. She went home happily and told her mother about the same. Her mother denied her to participate as the topic for the debate was on AIDS/HIV Neeta had a very clean argument with her mother upon this.What according to you, Neeta must have said her mother to impress her in regard to participate in the competition.

                                                     Section E

24.The graph given below is representing the reproductive cycle in females. Analyse the graph in regard of a normal menstrual cycle and answer the questions given below.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-5
(i) Identify the hormones marked as ‘X’ and ‘Y’.
(ii) Explain the ovarian phases during menstrual cycle.
(a) 5th day to 12th day of the cycle.
(b) 14th day of the cycle.
(c) 16th day to 25th day of the cycle.
(iii) What influence does hormones ‘X’ and ‘Y’ has on different Ovarian events labelled as (a), (b) and (c).
Or
Male and female gametes in human beings differs from each other in both structure and function. Enumerate some major differences between the two.

25.Given below is the type of global biodiversity representing the proportionate number of species of major taxa of plants.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-7

Observe the diversity carefully and answer the questions that follow

(i) Identify the most endangered group of plants among all categories.

(ii) What may be the reason behind such a less population of mosses and ferns?

(iii) Name the most advanced and the most primitive group of plants in a biodiversity given above.

(iv) Fungi, inspite of being heterotroph are able to sustain themselves as a large population. Explain.

Or

With the help of a flowchart explain what are the various major approaches to conserve biodiversity.

26.A single mutant allele is responsible for the abnormal fm n of haemoglobin (i.e Hbs). If it is present in a homozygous state (Hb s Hbs ), son develops a sickle  cell anaemia while shows few symptoms if it is found in a heterozygous state (HbA Hbs).On the basis of the above situation, work out a cross supposing a condition in which a women’s mother homozygous for allele marries a male who is heterozygous for the allele. Indicate the probability of having a normal or a diseased child for each of her pregnancy.

Or

Haemophilia and colour blindness are sex-linked recessive disorders being determined by the alteration or mutation in the single gene. Mention the pattern of inheritance of both disorders in human beings with a help of a cross.

 

Answers

                                                      Section A

1.Cross hybridisation among the selected parents during any plant breeding programme is meant to be a tedious and a time consuming process. Why?
Ans. This is because cross hybridisation as a step in a plant breeding programme involves a collection of pollen grains from the desired plants and other pollination techniques to incorporate desired traits.

2.In which phenomenon, a phenotype of the Fj hybrid offspring does not  resemble any of the parent and is intermediate between the expression of two alleles?
Ans. Incomplete Dominance.

3.It is often seen that replication of DNA does not initiate randomly anywhere in DNA, it instead begins at definite regions. Why is it so? Give reason.
Ans. Replication of DNA molecule begins at a definite region called Ori or (origin of replication) because it is this site which binds the pre-replication complex or a protein complex that recognises, unwinds and begins to copy DNA.

4.List two advantages of inbreeding in animals.
Ans. Advantages of inbreeding in animals are
(i) Necessary in evolving a pure line in any animal breed.
(ii) Increases homozygosity

5.Production of antibiotics has been widespread by the pioneering efforts of which two scientists.
Ans. Ernest Chain and Howard Florey have been production of antibiotics widespread by the pioneering.

                                                          Section B

6.How is diapause different from hibernation?
Ans. Hibernation is the phenomenon commonly depicted by cold-blooded animals, which escape cold by hiding themselves in shelters such as burrows muds, etc revealing minimum physiological activity. It is performed by large animals while, on the other hand, diapause is a stage of suspended development which takes place during unfavourable conditions like stress, etc. The growth and development gets resumed on the return of favourable conditions. Itis usually performed by microscopic or very small organisms like zooplanktons etc.

7.What are the two major aims and objectives behind the reproductive child health care programmes?
Or
Human Placenta acts as a structural and functional unit between a foetus and maternal body. Justify the statement giving any two basic function it performs.
Ans. The two major aims of reproductive and child health care programmes of the government are
(i) Creating awareness among the people about reproduction related issues.
(ii) Providing support and facilities for building a reproductively healthy society with special emphasis on the health of both mother and her child.
Functions of human placenta are as follows
(i) It facilitates the supply of oxygen and nutrients to the embryo.
(ii) It also secretes hormones that are necessary to maintain pregnancy such as HCG, HPL,Oestrogen, progesterone etc.

8.In what way does the cell mediated system works in a body when it gets infected?
Ans. The cell mediated immune system protects the body against foreign organisms that have managed to infect the body cells. The WBC’s involved in the cell mediated immunity are called T-cells which are actively involved with the disposal of antigens. They make proteins called T-cell receptors and help them to recognise a specific antigen.

9.Both linear DNA and plasmid DNA of same length having one site for a restriction endonuclease are cut and separated on agarose gel electrophoresis. The plasmid DNA shows one DNA band, while a linear DNA shows two fragments. State the reason behind the fact.
Ans. This may happen because plasmid is a circular DNA molecule. When cut with enzyme, it becomes linear but does not get fragmented. Whereas, a linear DNA molecule gets cut into two fragments. Hence, a single DNA band is observed for plasmid and two DNA bands fragments are usually observed for linear DNA during agarose gel electrophoresis.

10.Mention two functions of DNA polymerase.
Ans. Two functions of DNA polymerase are
(i)It add nucleotides to the DNA and removes RNA primer from DNA.
(ii)It also proofreads the created portion of DNA.

                                                       Section C

11.Draw a neat and well labelled diagram showing the reproductive system in human females.
Ans. Diagram of reproductive system in females is given below
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-1

12.Indian government had taken several measures to control the vehicular air pollution in Delhi and other cities of India. Enlist any three of them.
Ans. Three measures to control the vehicular air pollution are
(i) Reducing the use of fossil fuels.
(ii) Use of catalytic converters, electrostatic precipitators and other control devices.
(iii) Plantation of more trees especially the ones which accumulate pollutants and filters the air.

13.Amoebiasis is often caused by an intestinal parasite which being found in the large intestine of human beings. Give the name of the organism responsible for this. Also write the symptoms and mode of transmission responsible for the disease.
Ans. Amoebiasis is caused by Entamoeba histolytica.Symptoms The patient passes out blood and mucus with stools. He also experiences griping pain in the abdomen with a fever.                                         Mode of transmission is usually through faecal and oral route, by sexual transmission or by vectors such as flies, cockroaches, etc.

14.Enlist the main differences between the two types of nucleic acids found in living systems.
Or
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-2
(i) Identity the molecule X’ synthesised by ‘i’ gene. How does this molecule get inactivated?
(ii) Identity the structural genes that codes for {3-galactosidase.
(iii) When does the transcription of this gene gets stopped?
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-3
(i) Molecule ‘X’ synthesised by ‘i’ gene is a repressor protein. It gets inactivated on combining with an inducer molecule.
(ii) ‘z’ gene.
(iii) Transcription of gene stops in the following conditions
(a) When substrate lactose is not available.
(b) And when energy source i.e glucose is available to the cells.

15.Expand the term GMOs. Also explain the fact in what form a GMO differs from a hybrid?
Ans. GMOs stands for Genetically Modified Organisms.
It differs from a hybrid, as in order to produce a hybrid cross is done between genome of two species or strains. While, in case of GMOs, foreign genes are introduced in an organism and is usually maintained as an extra-chromosomal entity or gets integrated into the genome of an organism.

16.By taking an example of some of Australian marsupials and Australian placental mammals, briefly explain the phenomenon of adaptive radiation and convergent evolution in different species.
Ans. Adaptive radiation is known as the process of evolution of different species in a given geographical area starting from a point and literally radiating to the other areas of the habitat.  For example, many Australian marsupials, different from each other, such as kangaroo, sugar glider, etc had evolved from a common ancestral stock, but all within the Australian continent. Thus, when more than one adaptive radiation occur in an isolated geographical area, convergent evolution is said to occur.
Likewise Australian placental mammals also shows adaptive radiation in evolving into varieties of such placental mammals. Each one of these appear similar to the corresponding marsupial, e.g. placental wolf and Tasmanian wolf, anteater and numbat, etc.

17.It is merely important to test a new plant variety in a systematic way during different plant breeding programmes in a geographically vast country like India Justify.
Ans. Before the generation of new plants through the plant breeding programmes, they are need to be evaluated for their yield and other agronomic traits of quality, disease resistance, etc.
This testing is done on the farmer’s field itself for atleast three growing seasons, at different locations in the country representing all the agroclimatic zones, where the crop is usually grown. The material is then evaluated in comparison to the best available local crop cultivar known as a check or a reference cultivar.

18.(i) List any two conditions on which the development of a diploid cell depends.
(ii) If the number of chromosomes present in the meiocyte of a plant is 24, then
work out the number of chromosomes in the gamete, zygote and embryo of this plant.
Ans. (i) Zygote, a diploid cell is formed as a result of fusion of male and female gametes.
its development depends on the following two main conditions
(a) A type of life cycle of the organism.
(b) Environment to which it is exposed to.
(ii) If the number of chromosomes present in meiocyte (2n) is 24,

Then, the number of chromosomes in gamete will be (n) =12.

Number of chromosomes in zygote (2a?) will be = 24

And the Number of chromosomes in an embryo (2n) will be = 24

19.On a visit to a food processing industry, students saw that workers were working in a huge tank size vessels. Teacher explained them that these vessels are used for the process of fermentation.

(i) Write about the process of fermentation and how it takes place.

(ii) List some important applications of microbes in different industries.

Ans. (i) Fermentation is known as the process of conversion of carbohydrates to alcohol and C02with the help of microbes such as bacteria and yeast. Microbes via fermentation are  utilised for the synthesis of number of products that are valuable for human beings.

(ii) Some of the important applications of microbes are

(a) In the production of bread using baker’s yeast.

(b) To ferment fish, soybean, bamboo shoots, etc.

(c) To produce different varieties of cheese by fermentation via

(d) To produce wine, beer and other alcoholic drinks by fermentation.

(e) In the production of vinegar.

20.Biotechnologists identified the source and isolated different types of cry genes from the bacterium Bacillus thuringiensis and incorporated that into many crops. Briefly explain, how have these genes brought beneficial changes in the genetically modified crops and to the mankind?

Ans. Bt toxin genes were isolated from the bacterium Bacillus thuringiensis and was incorporated into several crops like cotton, tomato etc.

The choice of the genes depends on the crop and the targeted pest, as most Bt toxins are insect group specific. This toxin is coded by a gene named ‘cry’, e.g. Genes cry lAc and cry llAb control cotton bollworms and that of cry lAb controls corn borer.

21.The diagrammatic illustration of connection between the different trophic levels is given below
(i) Identify the type of ecological pyramid given below and explain what does the base and the apex of this pyramid is indicating.
(ii) Give examples of such types of ecological pyramids with respect to number and biomass.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-4
Ans. (i) The given pyramid is a spindle shaped ecological pyramid. The base and the apex of this pyramid is representing the producer (1st trophic level) and tertiary level consumer respectively.
(ii) Examples of such ecological pyramid are
(a)  Pyramid of number in a tree ecosystem, (b) Pyramid of biomass in a lake.

22.Branching descent and natural selection acts as two main key concepts of Darwinian theory of evolution. Discuss each concept with the help of a suitable example.
Ans. Branching descent is the ability of different species adapted to different habitats come from common ancestors, e.g. Darwin’s finches varieties arise from grain eaters, Australian marsupials evolved from common marsupials.
Natural selection is a process in which heritable variations helps in the survival of an organism and enable them to reproduce and produce large number of offsprings. There may be change in the frequency of genes and alleles in the future generations. It leads to the formation of a new species, e.g. evolution of marsupials of Australia from common ancestor.

                                                                  Section D

23.Neeta Class Xth student was selected by her teacher for the debate competition to represent her school. She went home happily and told her mother about the same. Her mother denied her to participate as the topic for the debate was on AIDS/HIV Neeta had a very clean argument with her mother upon this.What according to you, Neeta must have said her mother to impress her in regard to participate in the competition.
Ans. Neeta told her mother that inspite of being living in such an educated society, the awareness among our people has not yet reached to that extent which is actually needed. Thus, the forceful and constant reminding is eventually required. She also explained her motherthat due to this unawareness, our country is becoming over-populated and number of AIDS related cases are increasing constantly.

Apart from the unprotected sexual contacts, AIDS can also be spread due to following other reasons.

(i)       Use of contaminated needles and syringes.

(ii) Use of contaminated razors or other instruments used for piercing different body parts, e.g. pinna.

(iii) Transfusion of infected blood or blood products.

(iv) Organ transplant.                                                   (v) Parturition, etc.

Hence, it is not shameful to discuss about AIDS/HIV and ways to control it.

                                                     Section E

24.The graph given below is representing the reproductive cycle in females. Analyse the graph in regard of a normal menstrual cycle and answer the questions given below.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-5
(i) Identify the hormones marked as ‘X’ and ‘Y’.
(ii) Explain the ovarian phases during menstrual cycle.
(a) 5th day to 12th day of the cycle.
(b) 14th day of the cycle.
(c) 16th day to 25th day of the cycle.
(iii) What influence does hormones ‘X’ and ‘Y’ has on different Ovarian events labelled as (a), (b) and (c).
Or
Male and female gametes in human beings differs from each other in both structure and function. Enumerate some major differences between the two.
Ans. (i) Hormone’X’Luteinising Hormone (LH).  Hormone ‘Y’ Follicle Stimulating Hormone (FSH).
(ii) (a) Follicular phase (proliferative phase).
(b) Ovulatory phase (release of ovum).
(c) Luteal phase.
(iii) (a) FSH is secreted by the anterior pituitary, which stimulates the ovarian follicle to secrete  oestrogen, which in turn stimulates the proliferation of the endometrium of the uterine wall.
(b) Both LH and FSH attain a peak level in the middle of cycle (about 14th day). Rapid secretion of LH leading to its maximum level during the mid-cycle is called LH surge which induces the rupture of Graafian follicle and thereby the release of an ovum (ovulation).
(c) The remaining cells of ovarian follicles are further stimulated by the LH to develop  corpus luteum which secretes large amount of progesterone, a hormone essential for the maintenance of an endometrium.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-6

25.Given below is the type of global biodiversity representing the proportionate number of species of major taxa of plants.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-7
Observe the diversity carefully and answer the questions that follow
(i) Identify the most endangered group of plants among all categories.
(ii) What may be the reason behind such a less population of mosses and ferns?
(iii) Name the most advanced and the most primitive group of plants in a biodiversity given above.
(iv) Fungi, inspite of being heterotroph are able to sustain themselves as a large population. Explain.
Or
With the help of a flowchart explain what are the various major approaches to conserve biodiversity.
Ans. (i) Mosses are the most endangered group of plants.
(ii) Population of mosses and ferns is less may be due to the following reasons

  • Environment pollution                                   • Increase in urbanisation
  • Habitat destruction                                           • Expansion in agriculture

(iii)Angiosperm and algae respectively are the most advanced and primitive group of plants in a given biodiversity.
(iv)Fungi are heterotrophic in nature due to the lack of chlorophyll. They are able to sustain  themselves as a large population because of their ability of reproducing both asexually and sexually.
Or
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-8In-Situ
In-situ conservation involves the protection of species in their natural habitat
(i)Biodiversity hotspots are the regions of high levels of species richness and high degree of  endemism (that is species confined to that region and not found anywhere else). The total number of biodiversity hotspots are 34. Three hotspots, which cover India are Western Ghats/Sri Lanka, Indo-Burma and Eastern Himalaya.   (ii)Protected areas are ecologically rich and biodiversity rich regions. India has 14 Biosphere  Reserves, 90 National Parks and 449 Wildlife Sanctuaries. The first National Park set up in India was Jim Corbett National Park.
Ex-Situ
(i)Protection of gametes can be done by storing material in the places where stocks remain  viable for a longer period of time without harming their genetic variability.
(ii)Protection of threatened species comes under the category of off-site collections of  various wild and domesticated species. India has around 2,75,200 parks where animals which have become extinct in wild are maintained and has around 35 botanical gardens to collect, cultivate and display various different varieties of plant species.

26.A single mutant allele is responsible for the abnormal fm n of haemoglobin (i.e Hbs). If it is present in a homozygous state (Hb s Hbs ), son develops a sickle  cell anaemia while shows few symptoms if it is found in a heterozygous state (HbA Hbs).On the basis of the above situation, work out a cross supposing a condition in which a women’s mother homozygous for allele marries a male who is heterozygous for the allele. Indicate the probability of having a normal or a diseased child for each of her pregnancy.
Or
Haemophilia and colour blindness are sex-linked recessive disorders being determined by the alteration or mutation in the single gene. Mention the pattern of inheritance of both disorders in human beings with a help of a cross.
Ans.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-9
50% Homozygous for the Hbs allele
50% Heterozygous for both Hbs and HbA allele
Above cross shows that a child have the equal probability of developing into a normal child or with some symptoms of the disease. This therefore, proves that a women has no risk of giving birth to a child everytime she conceive.
Or
Haemophilia, a blood clotting disorder is majorly transmitted from an unaffected carrier female to some of the male offsprings. The gene for haemophilia is located on the X-chromosome. The possibility of female becoming haemophilic is extremely rare.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-10
This, indicates that for a female to become haemophillic in a homozygous condition, mother of such female should be carrier and a father should be haemophilic.
Colour blindness, on the other hand, is the inability to distinguish among some or all colours. In this disorder, mutant forms of genes changes the light absorbing capacity of sensory receptors inside the eyes. This trait is mainly common in men, but heterozygous women may also shows symptoms and passes on the disorder to some of her sons.
cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-1-12
Colour blindness, like any other disorder may also shows a criss-cross inheritance, i.e. it transmits from father to his daughter and from mothers to her son

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