CBSE Sample Papers for Class 12 Biology Solved 2016 Set 2

Section A

1.Enzyme cellulase can be used for the isolation of genetic material from plant cells only and not for animal cells. State a reason.

2.Owners of motor vehicles equipped with catalytic converters, are advised to use unleaded petrol. Why?

3.In what way, the Cry gene has brought beneficial changes in the genetically modified crops?

4.Mention any two major harms that may occur in future to the environment by the use of CFC’s.

5.Give any one similarity between the hydrach and Xerach successions of plants.

Section B

6.Differentiate between the following.
(i) Zoospore and zygote (ii) Homothallic and heterothallic

7.It is imperative for the physical and psychological well being that HIV/AIDS person should not be isolated from family and society Provide a reason.

8.State a reason why genetic variability acts as the root of any breeding programme?
Or
Biofortified maize and wheat are considered to be nutritionally much improved than the original crops. State any two reasons.

9.After observing an amazing diversity of creatures in Galpagos islands, Darwin made a conclusion that all varities of finches had evolved from an original seed-eating finches. Give reason.

10.It if often said that human female ovary produces only one egg in a month then how many eggs do you think would have been released by the mother to give birth to the identical twins.

Section C

11.Codominance acts as the phenomenon of resemblance of offsprings to both the parents. Justify the statement with the support of a well known example

15.Mechanism of sex determination differentiates from one another in every living beings. Describe in detail about such mechanism in case of humans, birds and grasshoppers respectively.

17.In what ways the biocontrol microbes controls their target species through a web of biological interactions? Explain giving some important examples.

18.It has been recorded that the temperature of the earth’s atmosphere has increased by 0.6°C.
(i)What has caused this increase? (ii)Explain its consequences.
Or
Due to uncontrolled excessive hunting, the population of tigers in a forest has become zero. Discuss the long-term effects of this situation on the population of deer in that forest.

19.(i) What happens when Meloidegyne incognitia consumes cells with RNAi gene? (ii) How agrobacterium vectors are also proved useful in genetic engineering?

21.Give reasons for the following
(i)Competition between intraspecific species tend to be more intense than the interspecific species.
(ii)Lichens shows obligate mutualism.
(iii)Population of different species are not capable of breeding with each other.

22.With the help of a flowchart, show the process that how does the genetic information from one strand of DNA is copied into RNA in case of prokaryotes.

Section D

Section E

24.What do you understand by the term antibodies in our body? Explain in detail about the different types and roles of antibodies.
Or
Drugs like LSD, barbiturates, amphetamines, etc are used as medicines to help patients with mental illness. However, excessive doses and abusive usage are harmful. Enumerate the major adverse effects of such drugs in humans.

25.(i) State the term antibody. Highlighting the structural importance of antibody molecule.
(ii) Name different types of antibodies found in the body mentioning the functions of each.

Answers

Section A

1.Enzyme cellulase can be used for the isolation of genetic material from plant cells only and not for animal cells. State a reason.
Ans. Cellulose is the substance that makes up the cell walls of most of the plants. Thus, enzyme cellulase is used forthe isolation of genetic material for plant cells only because animal cells do not have a cellulosic cell wall.

2.Owners of motor vehicles equipped with catalytic converters, are advised to use unleaded petrol. Why?
Ans. Unleaded petrol, i.e. petrol not treated with lead is eventually advised to use over leaded ” petrol or any other fuel because it does not emit harmful gases in the environment. And eventually does not causes any harm to it.

3.In what way, the Cry gene has brought beneficial changes in the genetically modified crops?

Ans. Cry gene being isolated from protein crystals of bacterium bacillus thuringiensis is been expressed in different crop plants in order to provide the resistance to the insects without the need for insecticides.

e.g. Bt potato, Bt tomato, Bt soybean etc.

4.Mention any two major harms that may occur in future to the environment by the use of CFC’s.

Ans. Continuous use of CFC’s may harm the environment in future in the following two ways

(i)May cause change in temperature of the climate

(ii)May cause failure of rainfall on earth.

5.Give any one similarity between the hydrach and Xerach successions of plants.

Ans.Similarity Both hydrach and Xerach successions leads to medium water conditions (mesic)

i.e. neither too dry (xeric) nor too wet (hydric) conditions.

Section B

6.Differentiate between the following.
(i) Zoospore and zygote (ii) Homothallic and heterothallic
Ans.

7.It is imperative for the physical and psychological well being that HIV/AIDS person should not be isolated from family and society Provide a reason.
Ans. The reason behind this fact is that HIV/AIDS is not transmitted by a mere touch or any physical contact rather it spreads through body fluids or by sharing infected needles. And by the transfusion of contaminated blood and blood products.

8.State a reason why genetic variability acts as the root of any breeding programme?
Or
Biofortified maize and wheat are considered to be nutritionally much improved than the original crops. State any two reasons.
Ans. Genetic variability is known as the ability or capability of a biological system (i.e. an individual and population that changes over time.) The variability of a trait eventually describes how much that trait tends to vary in response to environmental and genetic influences.
Or
Biofortified maize and wheat are nutritionally improved because of following two main reasons
(i)Hybrid maize is much rich in the amount of amino acids, lysine and tryptophan.
(ii)And hybrid wheat is much rich in the quantity of protein in it.

9.After observing an amazing diversity of creatures in Galpagos islands, Darwin made a conclusion that all varities of finches had evolved from an original seed-eating finches. Give reason.
Ans. He conclude that after originating from a common ancestral seed-eating stock, the finches must have radiated to different geographical areas and had undergone adaptive changes, especially in the type of beaks.

10.It if often said that human female ovary produces only one egg in a month then how many eggs do you think would have been released by the mother to give birth to the identical twins.
Ans. The identical twins are monozygotic nature and are produced from the two parts of the same zygote. Thus, only one egg has to released from the female ovary in order to give rise to the identical twins.

Section C

11.Codominance acts as the phenomenon of resemblance of offsprings to both the parents. Justify the statement with the support of a well known example.
Ans. Codominance is the phenomenon in which two alleles expresses themselves independently when present in a single organism, i.e. they neither show dominant recessive relationship nor they show an intermediate condition. Thus, it is true to say that codominance acts as the phenomenon of resemblance of offspring to both the parents.

For example, ABO blood group in humans.
The four phenotypes to blood groups in humans, A’, ‘B’, AB’, ‘O’ are produced by the three different alleles i.e. I^A, I^B and i of the immunogen gene.
The alleles I^A and l^B are completely dominant over ‘i’ an allele which means that when l^A and i are present in an individual only l^A expresses and on the other hand when l^B and i are present only I ⁸ will express, as an allele i does not produce any sugar.
But eventually in the case, where an individual possesses both l^A and l^B, both the alleles expresses their own types of antigens and the person is said to be having blood group AB.

12.Students while performing the experiment were given two different vectors in two different bacterial colonies being cultured in a chromogenic substrate. They observed that the bacterial colonies with cloning vector A were colourless while those with cloning vector B were blue in colour. Explain the phenomenon and the procedure behind the fact that the students were trying to figure out.
Ans. Students were working to differentiate recombinants and non-recombinants on the basis of production of colour in the presence of a chromogenic substrate.
During this phenomenon, a recombinant DNA is inserted within the coding sequence of an enzyme (1-galactosidase that results in an inactivation of the enzyme. Due to which, the bacterial colonies having plasmid inserted within it shows no colouration at all while those without plasmid will tends to show blue colour.

13.Gametogenesis is the phenomenon known for the formation of haploid gametes taking place in both males and females. Observe the flowchart given below highlighting the influence of process of gametogenesis and answer the questions that follows

(i)Identify the type of gametogenesis shown and in whom it takes place?
(ii)Explain the role of different hormones involved in the complete process.
Ans. (i) The process shown in the figure above is oogenesis, a type of gamete gametogenesis occurring in females.
(ii)The hormones involved in process of oogenesis in females similar to those involved in the process of spermatogenesis in males with a only difference that is oogenesis hormones acts on ovaries to stimulate the complete process.
The process of gametogenesis (oogenesis) in females begins in the part of the brain, (called hypothalamus) which releases a hormone called gonadotropin releasing hormone or GnRH that further, stimulates the release of hormones to acts on gonads.
In female, Follicle stimulating hormone acts on anterior pitutary because it stimulates the follicles present in the ovary containing the developing eggs. It also stimulates the ovary to produce the hormone, called oestrogen. This leads to the development of secondary sexual characteristics including the development of breasts and deposition of fat in some places. It also signals a drop in FSH and the production of LH (Leutinising hormone). This LH further causes the process ovulation (i.e. the release of the egg in the females).

14.If during the formation of male gametes, each pollen grain produces two male gametes. Then, reduce out the number of pollen grains would be required to fertilise five ovules present in a particular carpel. Give reasons to support your answer.
Ans. Each pollen grain generates to produce two male gametes that are carried through a pollen tube to the embryo sac. This pollen tube enters the embryo sac through the filiform apparatus of one of the synergids present at the micropylar end and releases two male gametes.
Out of these two male gametes, one fuses with the egg cell while, the other fuses with the secondary nucleus. Therefore, one pollen grain can fertilise only one ovule. It thus, process that in order to fertilise five ovules, five pollen grains will be required.

15.Mechanism of sex determination differentiates from one another in every living beings. Describe in detail about such mechanism in case of humans, birds and grasshoppers respectively.
Ans. Sex determination mechanism in humans, birds and grasshopper are as follows
(i)Humans In case of human beings, females have homogametic (XX) and males have heterogametic (XY) sex chromosome. Hence, in this case, the sperm is responsible for the determination of sex of the offspring.
(ii)Birds In case of birds, females have heterogametic (ZW) and males have homogametic (ZZ) sex chromosomes. Hence, egg is responsible for the sex determination of the offspring.
(iii)Grasshopper These show XO type of sex determination. Some species of grasshoppers bears X-chromosome while, others do not have sex chromosome. The female have homogametic (XX) and the male have heterogametic (XO) sex chromosome.

16.It is known that Global carbon in the biosphere is fixed through the process of photosynthesis. Explain, how is it done and also mention the ways by which carbon is eventually returned to the atmosphere?
Ans. The C0₂ is added to atmosphere mainly by the burning of the fossil fuels, volcanic activities and by the process of respiration. Decomposers also contribute substantially to C0₂ pool by their processing of waste materials and dead organic matter of land and oceans. About 4 x 10¹⁵ Kg of carbon is fixed annually in the biosphere through photosynthesis.

17.In what ways the biocontrol microbes controls their target species through a web of biological interactions? Explain giving some important examples.
Ans. Biological control refers to the use of biological methods for controlling plants diseases, pests and weeds etc.
Some examples of biological controls are
(i)Ladybird and dragonfly are used to get rid of aphids and mosquitoes.
(ii)Bacillus thuringiensis is used for the control of insects.
(iii)Fungus species Trichoderma are used in controlling infection in roots.
(iv)Baculoviruses are used as narrow spectrum insecticidal applications.

18.It has been recorded that the temperature of the earth’s atmosphere has increased by 0.6°C.
(i)What has caused this increase? (ii)Explain its consequences.
Or
Due to uncontrolled excessive hunting, the population of tigers in a forest has become zero. Discuss the long-term effects of this situation on the population of deer in that forest.
Ans.(i) Increase in atmospheric concentration of greenhouse gases (C0₂) has resulted in the rise of atmospheric temperature by 0.6°C (global warming).
(ii)Consequences for the increase in temperature are
(a)Weather and climate change by rising temperature and melting of ice caps, glaciers worldwide.
(b)Rise in water levels of seas and oceans. (c) Affects on food production.
(d) Sudden changes in rainfall pattern and frequent floods, droughts, hurricanes.
Or
If the number of predators (tigers) get reduced, the number of prey (deer) population will increase which will increase the pressure on the vegetation. As a result, plant population will decrease due to overgrazing. Little vegetation puts pressure on deer population and as a result deer population will decrease due to starvation, death or migration. Thus, ultimately the tigers (predators) will be affected. (3)
Sample Question Papers Biology Class Xllth

19.(i) What happens when Meloidegyne incognitia consumes cells with RNAi gene? (ii) How agrobacterium vectors are also proved useful in genetic engineering?
Ans. (i) If Meloidegyne incognitia consume cells with RNAi gene, silencing of specific mRNA occurs due to a complimentary dsRNA molecule formation which binds and prevents translation of mRNA (silencing) thus, causing death of the nematode.
(ii) Agrobacterium vectors are used for the introduction of nematode-specific genes into the host plant by producing both sense and antisense RNA into the host cells. As these two RNA’s are complementary to each other, they forms dsRNA and initiates RNAi silencing the specific mRNA of the nematode.

20.Ajay went with his father to see his friend in the hospital. They saw that doctor there was advising Ajay’s friend about the personal hygeine. What according to you is the importance of personal hygiene? List any six measures every person or a society should follow to prevent diseases from spreading by a contaminated food and water.
Ans. Preventive measures for diseases spread by contaminated food and water are
(i)Proper disposal of waste and excreta.
(ii)Cleaning and disinfection of pools, water tanks and other water reservoirs.
(iii)Storing raw and cooked food separately.
(iv)Cooking food in clean water and keeping it at safe temperature.
(v)Body should be clean, nails and hairs should be cut regularly
(vi)Hygenic practice should be adopted at hotels and restaurants.

21.Give reasons for the following
(i)Competition between intraspecific species tend to be more intense than the interspecific species.
(ii)Lichens shows obligate mutualism.
(iii)Population of different species are not capable of breeding with each other.
Ans.(i) Intraspecific competition is more intense because the requirements of individuals of same species are very similar.
(ii)Lichens set a good example of obligate mutualism because of the naturalistic relationship between the fungi and algae or cyanob bacteria in which an algae prepares food while, the fungus helps in the absorption of nutrients and provide protection.
(iii)Different species in a population are unable to breed with each other because of various types of biological and physical barriers.

22.With the help of a flowchart, show the process that how does the genetic information from one strand of DNA is copied into RNA in case of prokaryotes.
Ans. Transcription is the process of copying genetic information from one strand of DNA into RNA. It differs in procedure in both prokaryotes and Eukaryotes.
in prokaryotes, transcription is completed in three steps initiation, elengation and termination. Sigmafactor recognised the start signal and promoter region on DNA which then along with RNA polymerase binds to the promoter to initiate transcription.
The RNA polymerase after initiation of RNA transcription loses the factor but continues the polymerisation of ribonucleosides to from RNA
The RNA polymerase reaches the termination region of DNA. The RNA polymerase is separated from DNA-RNA hybrid, as a result nascent RNA separates. Thus process is called termination which is facilitated by a termination factor (rho).
In prokaryotes mRNA does not require any processing, so both transcription and translation occur in cytosol. It can be said that transcription and translation are coupled together.

Section D

23.While having lunch in canteen, Prateek was discussing with his friends about the movie in which the hero used to donate his sperms to help the couples undergoing infertility. Listening this one of Prateek’s friend argued with such thing and said that this type of activity and movies are just to earn money rather they should be banned. Discuss four points with appropriate explanation how Prateek will make him understand and his friends that helping out couples in such a way is not incorrect.
Ans. Prateek will share following points with his friend in the support of discussion
(i)Infertility is the condition in which man is unable to ejaculate enough semen containing sperm to fertilize the females egg.
(ii)Sperm donation can also help the couples if man has certain genetic defect such as haemophilia etc or couple is suffering from Rhesus incompatability.
(iii)By doing this a person can help couple’s family to continue their family.
(iv)Thus, donation of sperm if done in a legalised way is not a bad thing to do.

Section E

24.What do you understand by the term antibodies in our body? Explain in detail about the different types and roles of antibodies.
Or
Drugs like LSD, barbiturates, amphetamines, etc are used as medicines to help patients with mental illness. However, excessive doses and abusive usage are harmful. Enumerate the major adverse effects of such drugs in humans.
Ans. Antibody is a type of protein molecule produced by the 5-lymphocytes in response to pathogens. Each antibody is produced in response to a specific pathogen. It has four peptide chains. Antibody mediated response is called humoral immune response.
There are different types of antibodies produced in body at different time and at different locations.

Or
Harmful effects of drugs like LSD, barbiturates; amphetamines etc are
(i)Anxiety, shakiness, nausea, sweating and loss of mind control.
(ii)Reckless behaviour, vandalism and violence.
(iii)Lack of interest in personal hygiene, fluctuations in weight and appetite.
(iv)Depression, fatigue and aggressive behaviour.
(v)Social adjustment problems.
(vi)Withdrawal symptoms can be severe and life threatening.
(vii)Excessive doses of drugs may lead to coma and death due to respiratory failure, heart failure or cerebral haemorrhage.

25.(i) State the term antibody. Highlighting the structural importance of antibody molecule.
(ii) Name different types of antibodies found in the body mentioning the functions of each.
Ans. (i) Antibody is a type of a protein molecule produced by B-Lymphocytes in response to pathogens. T-Cells do not secretes antibodies directly however, they help B-Cells to produce them. Each antibody molecule has four peptide chains. Out of the four chains are Two small chains called light (landa) chains Two large chains called heavy (H) chains
An antibody is represented as H₂I₂ molecule. In our body, different type of antibodies are produced such as IgA, IgM, IgM, IgD: All these antibodies are found in blood.

26.(i)It has been seen since a long time that different organisms and their population are connected to each other through a special connection. Identify that connection and write about its different types.
(ii)Length of a food chain within an ecosystem generally limited to 3-4 trophic levels. Justify.
Ans.(i)Different organisms or population of an ecosystem are connected to each through a sequence or a series of connection called food chain. Through this chain the food and its contained energy is passed the food of a later member of a sequence. It is actually known as a feeding chain of organisms in an ecosystem.
There are mainly two types of food chains been found in the ecosystem
(a)Grazing food chain
(b)Deteritus food chain
(ii)The amount of flow energy in an ecosystem gets decreases with successive troppic levels as only 10% of energy gets transferred from one trophic level to the next successive level. And the energy is last in the form of respiration and other important activities for maintaining life.
If more trophic levels are present, the residual energy will be limited and decreases to such an extent that it cannot further support any trophic level by the energy flow. Thus, it is rightly said that the food chain is generally limited to the 3-4 trophic levels only.
For example

(Download Questions PDF)

[gview file=”https://resultscareer.files.wordpress.com/2015/12/cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-2-questions.pdf”]

(Download Solutions PDF)

[gview file=”https://resultscareer.files.wordpress.com/2015/12/cbse-sample-papers-for-class-12-sa2-biology-solved-2016-set-2-solutions.pdf”]