CBSE Sample Papers for Class 12 Biology Solved 2016 Set 9

Section A

1.DNA as a known polymer of nucleotides being linked to each other by 3′-5′ phosphodiester bond. Suggest the modifications that would prevent polymerisation of nucleotides.

2.State the property of retroviruses with an example.

3.Define reproductive health.

4.Follicular phase is considered to be the longest phase of the complete menstrual cycle. Discuss the changes that takes place during this phase.

5.If is often seen that a well growing herbaceous plant dies if it is transplanted outside. From its native forest. Give reason.

Section B

6.Human females experiences two major changes in her lifetime, i.e. menarche and menopause. State the significance behind these two events.
Or
Vinay came to his village after completing his studies and experiences a hike of growth in the population of his village. He felt concerned about this and decided to create awareness among people about family planning and its impacts. According to you what all ways he will suggest to control and check over population.

8.Differentiate between the two different types of interactions found among organism in a community with an example of each.

9.Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.

10.Write down the preventive measures to control the spread of common cold.

Section C

11.Zygote tends to pass through several developmental stages till the stage of an implantation. Discuss each stage briefly in a flowchart form.

12.(i) Draw the diagram of a bacteriophage.
(ii)Expand LAB. How does it work?

13.The crop varieties in India can be made disease resistant to overcome the food crisis. Justify the statement.

14.How does the rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen chemical composition of detritus?
Or
Discuss the condition of an ecosystem in the following situations
(i)if all producers will decrease in the number.
(ii)if all organisms of one trophic level will be eliminated or killed.
(iii)if all top carnivores population is removed.

15.Mention the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle.

16.(i) Which pill has been developed by CDRI, Lucknow?
(ii)State its contraceptive action.
(iii)Why it has been preferred over other pills?

17. DNA replication occur in small replication fork and not in its entire length.
(i)Why is DNA replication continuous and discontinuous in a replication fork?
(ii)Explain the importance of ‘origin of replication’ in a replication fork.

18.Dominance, co-dominance and incomplete dominance patterns of inheritance are different from each other. Discuss.

19.Identify the steps represented in the following process

20.Explain the following given below.
(i)The role of Y-chromosome in human sex determination.
(ii)Suppose a foetus has X and Y-chromosomes, but lacks receptors for the protein encoded by the SRY gene. Will the foetus develop as a male or as a female?

21.Out of in situ or ex situ conservation, which type of conservation measures helps the larger number of species to survive? Explain in detail.

22.Agrobacterium tumefaciens is known to be the natural method of gene transfer. Justify in support of the statement.

Section D

Section E

24.(i) Explain the structure of DNA.
(ii) Draw the diagram of its double helical model.
Or
Draw the labelled schematic structure of a transcription unit. Explain the function of each component of the unit in the process of transcription.

25.Diagrammatically explain the experimental setup in cloning and expressing a human gene into a bacteriom coli
Or
Highlight five areas, where biotechnology has influenced our lives.

26.(i) Mention any two significant roles that predation plays in nature.
(ii) Explain hydrarch succession.
Or
(i)Draw a ‘pyramid of numbers’ of a situation, where a large population of insects feed upon a very big tree. The insects in turn are eaten by small birds, which in turn are fed upon by big birds.
(ii)Differentiate between the pyramid of biomass of the above situation and the pyramid of numbers that you have drawn.

Answers

Section A

1.DNA as a known polymer of nucleotides being linked to each other by 3′-5′ phosphodiester bond. Suggest the modifications that would prevent polymerisation of nucleotides.
Ans.To present the polymerisation of nucleotides in a DNA, it either removes or replaces the 3-OH group in deoxyribose.

2.State the property of retroviruses with an example.
Ans.Retroviruses are the organisms having RNA as the genetic material. HIV is a member of this group.

3.Define reproductive health.
Ans.Reproductive health includes avoidance of any reproduction related problems like pregnancy,delivery, STDs, abortions, contraception, menstrual problems, infertility, etc.

4.Follicular phase is considered to be the longest phase of the complete menstrual cycle. Discuss the changes that takes place during this phase.
Ans.Follicular phase of menstrual cycle lasts for the complete 14 days. During this phase, the primary follicles in the ovary grows to become a fully mature Graafian follicle and simultaneously the endometrium layer of the uterus gets regenerated through proliferation.

5.If is often seen that a well growing herbaceous plant dies if it is transplanted outside. From its native forest. Give reason.
Ans.Herbaceous plant tends to die if is allowed to transplant from its native place due to the change in its microclimate.

Section B

6.Human females experiences two major changes in her lifetime, i.e. menarche and menopause. State the significance behind these two events.
Or
Vinay came to his village after completing his studies and experiences a hike of growth in the population of his village. He felt concerned about this and decided to create awareness among people about family planning and its impacts. According to you what all ways he will suggest to control and check over population.
Ans.Menarche and menopause defines the reproductive cycle of an adolescent female.Both terms are related to are common term known as menstruation ova cyclical monthly bleeding menarche or the start is the name given to the first menstrual period that usually occurs between the ages of 11-16 at reaching puberty. While, menopause or the end is the name given to the point in time when the flow or periods stops permanently. It usually occurs at an age of around 50 years.
Or
According to me, he will suggest to control and check over population in his villagers.
(i)Educational For example,Newspapers, magazines, radio, television etc
(ii)Increasing marriageable age At present, 18 year for female and 21 year for male.
(iii)Family planing Check high birth rate, started voluntary approach towards birth control measures.
Birth control methods are following
(i)Natural methods
(ii)Artificial (Barrier) method e.g. Condom, copper T, Oral contraceptive pills etc.

7.ELISA is the technique known to be based on the principles of interaction of antigen and antibody. Do you think that this technique can also be used in the molecular diagnosis of a genetic disorder such as phenylketonuria?
Ans.ELISA is known as the technique based on the ability of low molecular weights antibodies to
couple with enzymes to produce enzymatically active immunological conjugates. Thus, the test can only detect the presence of antigen and antibodies in the serum of a patient. On the other hand, phenylketonuria is the disease that occurs due to excess of phenylalanine in blood. Thus, it fails to detect such disorders.

8.Differentiate between the two different types of interactions found among organism in a community with an example of each.
Ans. Differences between mutualism and commensalism are given below

9.Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Ans.According to a recent study on fossils, a small terrestrial dinosaur with feathers covering the j limb and body was discovered. This search established thatfeathers evolved earlier than wing and may be functioning as thermoregulator to face adverse conditions. These newly developed feathers earlier helped in gliding and then flying.

10.Write down the preventive measures to control the spread of common cold.
Ans. Some preventive measures to control the spread of common cold are
(i) Covering the mouth and nose while sneezing.
(ii) Not sharing utensils, towels, handkerchiefs or food, etc.
(iii) Washing hands regularly after sneezing, coughing, blowing nose, etc.
(iv) Washing hands after touching surfaces like door handles, etc.

Section C

11.Zygote tends to pass through several developmental stages till the stage of an implantation. Discuss each stage briefly in a flowchart form.
Ans.

12.(i) Draw the diagram of a bacteriophage.
(ii)Expand LAB. How does it work?
Ans.(i) Diagram of Bacteriophage
(ii) LAB (Lactic Acid Bacteria) This bacteria tend to grow in milk and convert it into curd.

13.The crop varieties in India can be made disease resistant to overcome the food crisis. Justify the statement.
Ans.The conventional methods of breeding for disease resistance are hybridisation and selection.
Steps

Selection and screening germplasm for the resistance source (selecting a plant which is disease resistant).
Hybridisation of selected parents (plant is crossed or mated with plant having disease resistance).
Selection and evaluation of hybrids (offspring from above cross are selected and evaluated for desirable traits).
Testing and release of new varieties (after all the evaluations, testing is done and hybrid varieties are crossed).

14.How does the rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen chemical composition of detritus?
Or
Discuss the condition of an ecosystem in the following situations
(i)if all producers will decrease in the number.
(ii)if all organisms of one trophic level will be eliminated or killed.
(iii)if all top carnivores population is removed.

Ans.Rate of decomposition of detritus can be affected by the following abiotic factors in the respective ways
(i)Availability of oxygen, the rate of decomposition in the anaerobic condition, i.e. the absence of oxygen while increase in aerobic condition.
(ii)Chemical composition of detritus. Detritus rich in lignin and chitin has slower rate of decomposition, while, adetritus rich in nitrogen and water soluble substances such as sugar has a quicker rate of decomposition.
(iii)It acts as the most important abiotic factor among all. As rate of decomposition is high in warm and most environment. While, it is slower in the low temperature.
Or
(i)If the producers eventually decreases in the number due to any circumstances, the whole pyramid of energy would gets affected because producers makes the base of the pyramid. Also due to this, there well be more competition among the consumers for food and other resources and the consumers will eventually have to move to a new area to fulfil their needs.
(ii)By doing this to the organisms of one trophic level, the member of individuals in the next trophic level will decrease due to unavailability of the food, thereby, increasing the number of individuals in the lower trophic level because no one will be present to feed upon them. This will in turn cause an imbalance in the complete ecosystem.
(iii)In such condition, if all the top carnivorses or predators are removed, the world will had a devastating effect on the ecosystem from which it derives. Also there occurs a behavioural changes in the prey species due to which, they get degraded quickly and over run its habitat.

15.Mention the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle.
Ans.Gonadotropins (LH and FSH) are secreted by the anterior lobe of pituitary gland,
(i)Gonadotropins (LH and FSH) gradually increases during the follicular phase (proliferative phase) of menstrual cycle and stimulates follicular development as well as secretion of estrogen by the growing follicles.
(ii)LH and FSH attain a peak level in the middle of the cycle (about 14th day) and rapid secretion of LH induces rupture of Graafian follicle followed by ovulation (release of ovum).
(iii)LH stimulates transformation of Graafian follicle into corpus luteum.

16.(i) Which pill has been developed by CDRI, Lucknow?
(ii)State its contraceptive action.
(iii)Why it has been preferred over other pills?
Ans.(i) ‘Saheli’ has been developed by the CDRI, Lucknow.
(ii)It is an oral pill that inhibits ovulation and fertilisation.
(iii)It has been preferred over other pills as it is non-steroidal in nature and taken once a week.

17. DNA replication occur in small replication fork and not in its entire length.
(i)Why is DNA replication continuous and discontinuous in a replication fork?
(ii)Explain the importance of ‘origin of replication’ in a replication fork.
Ans.DNA molecule is long, so two strands cannot be separated in its entire length. The replication occurs within a small opening of the helix called as replication fork.
(i)The DNA-dependent DNA polymerase catalyses polymerisation only in one direction, that is 5′-> 3′. This creates some additional complications at the replicating fork. Consequently, on one strand (with polarity 3’—> 5′), the replication is continuous, while on the other (the template with polarity 5′-> 3′), it is discontinuous. These discontinuously synthesised fragments are later joined by the enzyme DNA ligase.
(ii)Origin of replication is a sequence of DNA at which replication is initiated. It is because of the requirement of ore that a piece of DNA if needed to be propagated during recombinant DNA procedure requires a vector.

18.Dominance, co-dominance and incomplete dominance patterns of inheritance are different from each other. Discuss.
Ans.Differences between dominance, Incomplete dominance and co-dominance are given below

19.Identify the steps represented in the following process
Ans. A — Collection of germplasm
B — Cross hybridisation among selected plants.
C — Selection and testing of superior recombinants.

20.Explain the following given below.
(i)The role of Y-chromosome in human sex determination.
(ii)Suppose a foetus has X and Y-chromosomes, but lacks receptors for the protein encoded by the SRY gene. Will the foetus develop as a male or as a female?
Ans.(i) The Y-chromosome contains the SRY gene. It acts as a switch for other sex determining genes that activate in the embryo, so thatthe SRY gene develops as a male and dismantles all the female embryonic structures.
(ii) The foetus will develop as a female without SRY protein receptors, the signal to develop as a male will never be received.

21.Out of in situ or ex situ conservation, which type of conservation measures helps the larger number of species to survive? Explain in detail.
Ans.In situis onsite conservation, which implies that species are conserved in their natural habitat. To conserve species in their natural habitat, the entire ecosystem has to be conserved, which include other organisms, biotic and abiotic component of the ecosystem associated with the target species. Hence, in situconservation helps in the survival of larger number of species.

22.Agrobacterium tumefaciens is known to be the natural method of gene transfer. Justify in support of the statement.
Ans.Agrobacterium tumefaciens,a pathogen of several dicot plants is able to deliver a piece of DNA known as fDNA (transfer DNA) to transform normal plant cells into a tumour and direct these tumour cells to produce the chemicals required by the pathogen.
The tumour inducing Ti plasmid of Agrobacterium tumefaciens has now been modified into a cloning vector, which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of our interest into a variety of plants.

Section D

23.Rita’s sister when given birth to a child been advised by the Doctor to feed her child during the initial periods for upto 6 months. As breast feeding is beneficial for both. But, she denies to do so as she feels that her figure will be spoiled. As a biology student how will you moralise her sister. Also give the advantages related to this.
Ans.Breast milk contains antibodies (IgA) that actually helps the newborns to fight against viruses,bacteria and other foreign agents that enters the body. It also lowers the body’s risk of having asthma, any sort of allergies, etc. Also, it is wrong to think that breast feeding spoils girls figure because it is not related to any type of issues. Infact womens often feel relaxed while breast feeding. Also it helps women to lower the risk of many diseases.

Section E

24.(i) Explain the structure of DNA.
(ii) Draw the diagram of its double helical model.
Or
Draw the labelled schematic structure of a transcription unit. Explain the function of each component of the unit in the process of transcription.
Ans.(i) DNA is a long polymer of deoxyribonucleotides.Double helical structure of DNA is the most accepted model. It was given by James Watson and Francis Crick in 1953.
Salient features of DNA are

It is made up of two polynucleotide chains, where the backbone is constituted by sugar-phosphate and the base pairs project inside.
The two chains have anti-parallel polarity. It means that if one chain has polarity 5′ -> 3′ the other has 3′ -> 5′.
Bases are paired through the hydrogen bond forming base pairs.
The two chains are coiled in a right handed fashion. The pitch of the helix is 3.4 nm and there are 10 bp in each turn. Consequently, the distance between a bp is 0.34 nm.
Plane of one base pair stacks over the other in double helix which provides stability to the structure.

(ii) Double Helical Model

Or

Functions of components of transcription unit are

Promoter (DNA sequence) — Provides binding site for the RNA polymerase.
Structural genes — Code for enzymes/proteins and transcribe the /77RNA for the same.
Terminator (sequence of bases) — Defines the end of transcription process.
DNA strand with 3′ – 5′ polarity — Acts as the template for transcription of mRNA.
DNA strand with 5′ – 3′ polarity — Coding strand; it does not code for RNA.

25.Diagrammatically explain the experimental setup in cloning and expressing a human gene into a bacteriom coli
Or
Highlight five areas, where biotechnology has influenced our lives.
Ans.The multiple identical copies of specific template DNA can be produced by DNA cloning. It can be carried out by the use of a vector to carry specific foreign DNA fragment into the host cell. The mechanism of cloning and transfer of a gene for human growth hormone into E. coli is diagrammaticaiiy represented below.

Or
Biotechnology has influenced our lives in the following ways

It has provided us with genetically modified crops of better quality and high nutrient value.
It has made available better and safer recombinant vaccines.
It has also helped to develop transgenic animals that can produce human proteins.
It has enabled gene therapy for curing various genetic diseases.
Environment pollution has also been taken care of with the help of genetically engineered microbes.

26.(i) Mention any two significant roles that predation plays in nature.
(ii) Explain hydrarch succession.
Or
(i)Draw a ‘pyramid of numbers’ of a situation, where a large population of insects feed upon a very big tree. The insects in turn are eaten by small birds, which in turn are fed upon by big birds.
(ii)Differentiate between the pyramid of biomass of the above situation and the pyramid of numbers that you have drawn.
Ans.(i) Predation plays following two important roles in nature
(a)They keep the prey populations under control.
(b)And act as conduits for energy transfer across trophic levels.
(ii) Process of hydrarch succession is as follows
(a)Submerged Stage The pioneer species in an aquatic habitat are phytoplanktons.
(b)Floating Stage Floating plants begin to appear with the rise in shallowness of the pond. Later on free floating plants like Lemna, Azo/la, Wolfia, grows profusely to cover the water surface.
(c)Marsh-Meadow Stage As the free water is changed to swampy land, the water plants give way to swampy plants such as sedges and rushes.
(d)Woodland (climax) Stage With time, many smaller species of trees invade the area and climax community appears.

(ii) Incase of pyramid of number for first two steps, number increases, but after that it starts decreasing. Whereas, in pyramid of biomass there is no clear trend.

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