Students can access the CBSE Sample Papers for Class 12 Biology with Solutions and marking scheme Term 2 Set 8 will help students in understanding the difficulty level of the exam.

CBSE Sample Papers for Class 12 Biology Standard Term 2 Set 8 with Solutions

Time Allowed: 2 Hours
Maximum Marks: 40

General Instructions:

  • All questions are compulsory.
  • The question paper has three sections and 13 questions. All questions are compulsory.
  • Section-A has 6 questions of 2 marks each; Section-B has 6 questions of 3 marks each; and Section-C has a case-based question of 5 marks.
  • There is no overall choice. However, internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.
  • Wherever necessary, neat and properly labeled diagrams should be drawn.

Section – A

Question 1.
Humans have innate immunity for protection against pathogens that may enter the gut along with food.
What are the two barriers that protect the body from such pathogens? [2]
Answer:
Pathogens enter the body through food and water and the two barriers that protect the body from such pathogens are:

  • Physical barriers: Mucus coating of the epithelium lining the gastrointestinal tract and respiratory tract helps in trapping microbes entering our body.
  • Physiological barriers: Low pH in stomach and presence of bacteriolytic lysozyme in tears, saliva and other secretions of body prevent the growth of bacteria.

Question 2.
A patient admitted in ICLI was diagnosed to have suffered from myocardial infarction. The condition of coronary artery is depicted in the image below.
Name two bioactive agents and their mode of action that can improve this condition.
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 1
Substantiate by giving two reasons as to why a holistic understanding of the flora and fauna the cropland is required before introducing an appropriate biocontrol method. [2]
Answer:
Myocardial infarction commonly known as a heart attack, occurs when there is insufficient supply of blood to some parts of heart, causing damage to the heart muscle.
The two bioactive agents and their mode of action that can improve this condition are:
(1) Streptokinase (produced by the bacterium Streptococcus) is used as a ‘clot buster’ for removing clots from the blood vessels of patients who have undergone myocardial infarction.
(2) Statins (produced by the yeast Monascus purpureus) act as blood cholesterol lowering agents.
OR
Eradication of pests will disrupt predator-prey relationships, where beneficial predatory and parasitic insects which depend upon flora and fauna as food or hosts, may not be able to survive. Holistic approach ensures that various life forms that inhabit the field, their life cycles, patterns of feeding and the habitats that they prefer are extensively studied and considered.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

Question 3.
Identify the compound having chemical structure as shown below. State any three of its physical properties. [2]
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 2
Answer:
The chemical structure is shown above is Morphine (alkaloid).
The physical properties are: It appears as a white, odourless, crystalline compound.

Question 4.
Water samples were collected at points A, B and C in a segment of a river near a sugar factory and tested for BOD level. The BOD levels of samples A, B and C were 400 mg/L, 480 mg/L and 8 mg/L respectively. What is this indicative of? Explain why the BOD level gets reduced considerably at the collection point C? [2]
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 3
Answer:
At collection points A and B, the BOD level is high due to high organic pollution caused by sugar factory and sewage discharge in the river. At the collection point C, the water was released after secondary treatment/ biological treatment (where vigorous growth of useful aerobic microbes into floes consume the major part of the organic matter present in the river water or effluent due to sugar factory and sewage discharge) which is clearly indicated by the reduced BOD.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

Question 5.
An ecologist studied an area with population A, thriving on unlimited resources and showing exponential growth and introduced population B and C to the same area.
What will be the effect on the growth pattern of the population A, B and C when living together in the same habitat? [2]
Answer:
This interaction of the populations A, B and C will lead to competition for resources. Since the supply of resources is limited for the combined needs of all individuals, natural selection plays an important role and eventually the ‘fittest’ individuals will survive and reproduce.

Since the resources for growth will become finite and limiting, and population growth will no longer remain exponential but becomes realistic.

Question 6.
With the decline in the population of fig species it was noticed that the population of wasp species also started to decline. What is the relationship between the two and what could be the possible reason for decline of wasps?
OR
With the increase in the global temperature, the inhabitants of Antarctica are facing fluctuations in the temperature. Out of the regulators and the conformers, which of the two will have better chances of survival?
Give two adaptations that support them to survive in the ambient environment? Give one suitable example. [2]
Answer:
A mutualistic relationship is established between two organisms of different species that work together or live together and each is getting benefitted from the relationship. This is the example of the relationship between the plant and pollinator. Fig depends on wasp for pollination, and wasp depends on fig for obtaining food and shelter. With the decline in population of figs, wasp loses its source of food and shelter while if wasp is declined the fig will not get pollinated.
OR
Conformers: They are the organisms which cannot maintain a constant internal environment with respect to changing external environmental conditions like body temperature and osmotic concentration. Eg. fishes, etc.

Regulators: Organisms which can maintain homeostasis, maintain constant body temperature and osmotic concentration. Eg. mammals.

Hence regulators have better survival chances. The two adaptations that support them to survive in the ambient environment is thermoregulation (maintaining constant body temperature) and osmoregulation (maintaining osmotic pressure). E.g. Birds or mammals.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

SECTION – B

Question 7.
How do normal cells get transformed into cancerous neoplastic cells? Elaborate giving three examples of inducing agent.
OR
A person is suffering from a high-grade fever. Which symptoms will help to identify if he/she is suffering from Typhoid, Pneumonia or Malaria? [3]
Answer:
Normal cells get transformed into cancerous neoplastic cells due to the effect of carcinogens.
Carcinogenic agents could be physical, chemical or biological agents that changes the normal sequence of DNA. They are:

  • Ionising radiations like X-rays and gamma rays
  • Non-ionizing radiations like UV.
  • Chemical carcinogens present in tobacco smoke
  • Cellular oncogenes (c-onc) or proto-oncogenes, when activated under certain conditions cause cancer. Viruses with oncogenes can transform normal cells to cancerous cells.

OR
Typhoid which is caused by Salmonella typhi and transmitted through contaminated food and water. The person suffering from typhoid has sustained high fever (39° to 40°C), weakness, stomach pain, constipation, headache and loss of appetite.

Pneumonia is caused by Diplococcus pneumonia and spread through droplet infection . The person suffering from pneumonia has fever, chills, cough and headache; and the lips and fingernails turn gray to bluish.

Malaria is transmitted by the bite of female anopheles mosquito and is caused by Plasmodium. The person suffering from malaria has chills and high fever recurring every three to four days.

Question 8.
Recognition of an antigenic protein of a pathogen or exposure to a pathogen occurs during many types of immune responses, including active immunity and induced active immunity.
Specify the types of responses elicited when human beings get encountered by a pathogen. [3]
Answer:
When our body encounters an antigenic protein or a pathogen for the first time it produces a response which is of low intensity and our body retains memory of the first encounter.

  • The subsequent encounter with the same pathogen elicits a highly intensified response called as anamnestic response and is carried out with the help of two special types of lymphocytes present in our blood, B lymphocytes, and T-lymphocytes.
  • The B-lymphocytes produce an army of proteins in response to these pathogens into our blood to fight with them. These proteins are called antibodies. Antibodies are specific against specific pathogens. The T-cells themselves do not secrete antibodies but help B-cells produce them and also play an important role in graft rejection.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

Question 9.
In a pathological lab, a series of steps were undertaken for finding the gene of interest. Describe the steps, or make a flow chart showing the process of amplification of this gene of interest. [3]
Answer:
PCR is the technique of amplification of small fragment of DNA. The technique was developed by Kary
Mullis in the 1980s.
The flow chart shows the three steps involved in the process of PCR showing below:
(i) Denaturation: The DNA strands are treated with a temperature of 94°C (Heat) which results in denaturation of DNA caused due to break down of hydrogen bonds which separates double- stranded DNA to single-stranded DNA. The temperature at which 50% of the dsDNA is denatured is known as the melting temperature (Tm) and is determined by G + C content, the length of the sample, and the concentration of ions (Mg2+).

(ii) Annealing: The primers are added which get anneal to the complementary strands and provides the site of attachment of DNA polymerase. During this step, the sample is cooled to 40-60°C.

(iii) Extension: The DNA polymerase (Taq DNA polymerase) facilitates the extension of both the strands of DNA resulting in millions of copies in few cycles. This final step occurs at 70-75°C. At this temperature taq polymerase can synthesize and elongate the target DNA quickly and accurately.
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 4

Question 10.
‘The Evil Quartet’ describes the rates of species extinction due to human activities. Explain how the population of organisms is affected by fragmentation of the habitats.
Introduction of alien species has led to environmental damage and decline of indigenous species. Give any one example of how it has affected the indigenous species?
Could the extinction of Steller’s sea cow and passenger pigeon be saved by man? Give reasons to support your answer. [3]
Answer:
(a) The Evil Quartet is the concept which explains the reasons which cause a decrease in the number of species. The reasons are overexploitation, loss of habitat, introduction of the exotic species and co- extinction of species.
When a large habitat is broken into small fragments due to various activities, mammals and birds requiring large territories and certain animals with migratory habitats are badly affected, leading to population decline.

(b) Invasive alien species are plants, animals that are non-native to an ecosystem, may cause environmental harm or may pose an adverse impact upon biodiversity, including decline or elimination of native species – through competition, predation, or transmission of pathogens and the disruption of local ecosystems and ecosystem functions.
E.g., Nile perch introduced in lake Victoria eventually led to the extinction of an ecologically unique assemblage of more than 200 species of cichild fish. Parthenium/Lantana/water hyacinth caused environmental damage and threat to our native species. African catfish-C/arias gariepinus introduced for aquaculture purposes is posing a threat to the indigenous catfishes in our rivers.

(c) Yes; the extinction of Steller’s sea cow and passenger pigeon could be saved by man. Humans have overexploited natural resources for their ‘greed’ rather than ‘need’ leading to extinction of these animals. Sustainable harvesting could have prevented extinction of these species.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

Question 11.
(a) The image shown below is of a sacred grove found in India. Explain how has human involvement helped in the preservation of these biodiversity rich regions.
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 5
(b) Value of Z (regression coefficient) is considered for measuring the species richness of an area. If the value of Z is 0.7 for area A ,and 0.15 for area B, which area has higher species richness and a steeper slope?
Answer:
(a) India’s history of religious and cultural traditions emphasized the protection of nature. In many cultures, tracts of forest are set aside, all the trees and wildlife within are venerated and given total protection. Sacred groves in many states are the last refuges for a large number of rare and threatened plants.
(b) The value of regression coefficient is 0.7 for area A and thus Area A will have more species richness and a steeper slope. [3]

Question 12.
The image below depicts the result of gel electrophoresis
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 6
If the ladder represents sequence length upto 3000 base pairs (bp),
(a) Which of the bands (I – IV) correspond to 2500 bp and 100 bp respectively?
(b) Explain the basis of this kind of separation and also mention the significance of this process. [3]
Answer:
(a) The maximum length of ladder of gel shown is 3000 bp. Band III corresponds to 2500 base pairs, and Band IV corresponds to 100bp.

(b) The fragments will resolve according to their size. The shorter sequence fragments would move farthest from well as seen in Band IV (100 bp) which is lighter as compared to Band III which is heavier being 2500 base pairs.
The significance of electrophoresis is to purify the DNA fragments for use in constructing recombinant DNA by joining them with cloning vectors.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

SECTION – C

Question 13.
Some restriction enzymes break a phosphodiester bond on both the DNA strands, such that only one end of each molecule is cut and these ends have regions of single stranded DNA. BamHl is one such restriction enzyme which binds at the recognition sequence, 5′-GGATCC- 3′ and cleaves these sequences just after the 5′- guanine on each strand.
(a) What is the objective of this action?
(b) Explain how the gene of interest is introduced into a vector.
(c) You are given the DNA shown below.
5′ ATTTTGAGGATCCGTAATGTCCT 3′
3′ TAAAACTCCTAGGCATTACAGGA 5′
If this DNA was cut with BamHI, how many DNA fragments would you expect? Write the sequence of these double-stranded DNA fragments with their respective polarity.
(d) A gene M was introduced into E.coli cloning vector pBR322 at BamHI site. What will be its impact on the recombinant plasmids? Give a possible way by which you could differentiate non recombinant to recombinant plasmids. [5]
OR
GM crops especially Bt crops are known to have higher resistance to pest attacks. To substantiate this, an experimental study was conducted in 4 different farmlands growing Bt and non Bt-Cotton crops. The farm lands had the same dimensions, fertility and were under similar climatic conditions. The histogram below shows the usage of pesticides on Bt crops and non-Bt crops in these farm lands.
CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions 7
OR
(a) Which of the above 4 farm lands has successfully applied the concepts of biotechnology to show
better management practices and use of agrochemicals? If you had to ci±ltivate, which crop would
you prefer (Bt or non- Bt) and why?
(b) Cotton boliworms were introduced in another experimental study on the above farm lands wherein
no pesticide was used. Explain what effect would a Bt and non Bt crop have on the pest.
Answer:
(a) The two different DNA molecules will have compatible ends to recombine when cut with same
restriction enzymes.

(b) Restriction enzyme cuts the DNA of the vector and then ligates the gene of interest into the DNA o1
the vector.

(c) 2 fragments
5’ A1TFTGAG 3’5’GATCCGTAATGTCCT 3’
3’ TAAAACTCCTAG 5’.3’GCATI’ACAGGA 5’

(d) BamH1 site will affect tetracycline antibiotic resistance gene, hence the recombinant plasmids will
lose tetracycline resistance due to inactivation of the resistance gene.
Recombinants can be selected from non-recombinants by plating into a medium containing
tetracycline, as the recombinants will not grow in the medium because the tetracycline resistance
gene is cut and non-recombinants will grow in medium containing tetracycline.
OR
(a) Farm land II requires less application of pesticide.
I would prefer Bt crop as it involves no application of fertilizers and pesticides and shows more
yield when compared to non Bt crop.
Because the use of pesticides is highly reduced for Bt crop. Decrease of pesticide used is also more
significant for Bt crop.

CBSE Sample Papers for Class 12 Biology Term 2 Set 8 with Solutions

(b) In Bt cotton a cry gene has been introduced from bacterium Bacillus thuringiensis (Bt) which causes
synthesis of a toxic protein. This protein becomes active in the alkaline gut of boliworm feeding
on cotton, punching holes in the lining of the gut, causing death of the insect. However; a non-Bt
crop will have no effect on the cotton bollworm and the yield of cotton will decrease, non-Bt will
succumb to pest attack.