CBSE Class 12 Biology Question Paper (Outside Delhi 2022) Term-II with Solutions

Students can use CBSE Previous Year Question Papers Class 12 Biology with Solutions and CBSE Class 12 Biology Question Paper (Outside Delhi 2022) Term-II to familiarize themselves with the exam format and marking scheme.

CBSE Class 12 Biology Question Paper (Outside Delhi 2022) Term-II with Solutions

Time Allowed: 2 Hours
Maximum Marks: 35

General Instructions:

1. This question paper contains 13 questions. All questions are compulsory.
2. This question paper has three Sections – Section A, B and C.
3. 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.
4. There is no overall choice. However, internal choices have been provided in some questions. A candidate has to attempt only one of the alternative in such questions.
5. Wherever necessory, neat and properly labelled diagrams should be drawn.

Section – A

Question 1.
State the impact of constant mechanical agitation and pumping of air in the aeration tank on the sewage during the biological treatment.
(a) Cattle excreta is important source for producing a domestic fuel. Name the fuel and write its main components.
(b) Write the biological process that is responsible for the production of this fuel.
Answer:
The primary effluent is passed into large aeration tanks, where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into floes (masses of bacteria associated with fungal filaments to form mesh like structures). While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the BOD (biochemical oxygen demand) of the effluent.

OR

(a) The excreta of cattle, commonly called gobar, is rich in bacteria. Dung can be used for generation of biogas, commonly called gobar gas. Biogas contains methane gas.

(b) Some bacteria, which grow anaerobically, fermented the cattle excreta in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as a source of energy as it is inflammable.

Note
Biochemical oxygen demand (BOD):
BOD is defined as the amount of oxygen consumed by bacteria and other micro-organisms ’while they decompose organic matter under aerobic conditions at a specified temperature.

Question 2.
Mention the two types of acquired immune response present in our body. Give one major role of each.
Answer:
The two type of acquired immune response present in human body are-

(a) Humoral immune response
(b) Cell- mediated immunity

Major roles are:

1. Humoral immune response protects against extracellular virus and bacteria.
2. Cell- mediated immunity is responsible for the graft rejection.

Question 3.
The histogram given below representing the data for annual shark harvest in the great barrier reef / coral reed located on the east coast of Queensland, Australia, Study the histogram and answer the questions that follow.

(a) Write your interpretation of the data given.
(b) Write the impact on the biodiversity of the area that you can interpret on the basis of given data.
OR
‘Stability of community depends upon its species richness.” How did David Tilman show this experimentally?
Answer:
(a) The annual catching data of shark is gradually increases and reached upto 1200 tonnes in a year of 2003.

(b) Healthy shark populations may aid the recovery of coral reefs. But if shark populations in a coral reef system are severely reduced due to commercial fishing, herbivorous fish that graze on algae may also decline. Fewer herbivorous fish keep algae growth in check, which in turn, harms coral reefs.

OR

A stable community should not show too much variation in productivity from year to year; it must be either resistant or resilient to occasional disturbances, and it must also be resistant to invasions by alien species. Tilman found that plots with more species showed less year to-year variation in total biomass. He also showed that in his experiments, increased diversity contributed to higher productivity. The rich biodiversity is not only essential for ecosystem health but imperative for the very survival of the human race on this planet.

Question 4.
Name the source organism (scientific name) that produces statins. Mention its use in medical field and how does it act.
Answer:
Statins produced by the yeast Monascuspurpureus.
Statins have been commercialised as blood cholesterol lowering agent. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

Note
Statins are a group of medicines that can help lower the level of Low-density lipoprotein (LDL) cholesterol in the blood. LDL cholesterol in often referred to as “bad cholesterol” and statins reduce the production of it inside the liver.

Question 5.
(a) Give an example of viral biocontrol agent.
(b) Why are they considered to be desirable when an ecologically sensitive area is being treated?
Answer:
(a) Baculoviruses is the one of the best example of viral biocontrol agent.

(b) Baculoviruses showed no negative impacts on plants, mammals, birds, fish or non-target insects. This is especially desirable when beneficial insects are being conserved to aid in the overall integrated pest management (IPM) programme, or when an ecologically sensitive area is being treated.

Question 6.
Study the graph given below, showing the population growth curves ‘A’ and ‘B’ respectively. Answer the following questions:

(a) What is ‘Carrying Capacity’ in respect of Curve ‘B’ indicative of’?
(b) Mention the action of possible natural forces that could have lead to curve ‘B’
Answer:
(a) In logistic growth, a population’s per capita growth rate gets smaller and smaller as population size approaches a maximum imposed by limited resources in the environment, known as the carrying capacity (K).
dN/dt = rN(K – N/K)

(b)

• Resources for growth for most animal populations are finite and become limiting sooner or Later, the Logistic growth model is considered a more realistic one.
• The ‘fittest’ individual will survive and reproduce.
• In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible.

Section B

Question 7.
(a) What does the equation dN/dt = rN express in terms of population growth?
(b) Write the significance of ’r’ in a population survey.
Answer:
(a) The equation dN/dt = rN express for Exponential growth.

(b) The r in this equation is called the ‘intrinsic rate of natural increase’ and is a very important parameter chosen for assessing the impacts of any biotic or abiotic factor on population growth.

Question 8.
(i) Statetheroleofaselectablemarkerinr-DNAtechnology.
(ii) Name one such selectable marker which is considered to be useul for E.coli.
(iii) Give one reason why is it considered to be a useful marker.
OR
What are plasmids? How are they different from cloning vectors? Give one example each for a viral and a bacterial cloning vector.
Answer:
(i) A selectable marker helps in identifying and eliminating non-transformants and selectively permitting the growth of the transformants.
(ii) Ampicillin is considered useful selectable marker for E. coil.
(iii) The selectable markers are the gene substances that are injected into the cell so that they can offer
resistance to the action of the antibiotics.

OR

Plasmids are autonomously replicating circular extra — chromosomal DNA, present only in prokaryotic organisms.
Plasmids can able to replicate within bacterial cells independent of the control ofchromosomal DNA. While cloning vector is a small piece of DNA, taken from any organism into which a foreign DNA fragment can be inserted for cloning purposes.
The example of viral cloning vector is Bacteriophage.
The example of bacterial cloning vector is Ecoli.

Question 9.
Explain giving reason the action plan followed by organic farmers that support their key belief “biodiversity furthers health of crop lands.”
Answer:
Yes, the organic farmer indeed believes that biodiversity furthers health.

• An organic farmer depends on composting and using absolutely natural ingrediats in conducting his cultivation.
• There is no use of pesticides or chemicals and crop cultivation is done in an all-natural environment.
• Farmer uses biodiversity to counter the problems of cultivation and by doing so he believes that this helps in overall health improvement.
• As no chemical is usod and only natural produce is utilized so this indeed improves the health of all.

Note
Organic farming can be defined as “an integrated farming system that strives for sustainability, the enhancement of soil fertility and biological diversity. It increased species richness by about 30%

Question 10.
Bio-diversification of life started to occur almost 3 billion years ago. Since then new species have been evolving and then disappearing en masse from earth.
(a) How many episodes of mass extinctions of species have already taken place and which one is in progress in the current era?
(b) How is current episode in progress different from the previous episodes and why? Explain.
Answer:
(a)’ During the long period (>3 billion years) since the origin and diversification of life on earth, there were five episodes of mass extinction of species.
Presently, 12 per cent of all bird species, 23 per cent of all mammal species, 32 per cent of all amphibian
species and 3 per cent of all gymnosperm species in the world face the threat of extinction.

(b) The difference is in the rates between the current episode and the previous episode; the current species extinction rates are estimated to be 100 to 1,000 times faster than in the pre-human times and our activities are responsible for the faster rates. Ecologists warn that if the present trends continue, nearly half of all the species on earth might be wiped out within the next 100 years.

Question 11.
(i) Name three molecular diagnostic techniques for diagnosis of a disease.
(ii) List three advantages of molecular diagnostic techniques over conventional method of diagnosis.
Answer:
(i) Recombiant DNA technology, Polymrase Chain Reaction (PCR) and Enzyme Linked Immuno sorbent Assay (ELISA) are some of the techniques that serve the purpose of early diagnosis.

(ii) Advantages of molecular diagnostic techniques are:

• It is being used to detect mutations in genes in suspected cancer patients too.
• It is a powerful technique to identify many other genetic disorders.
• Infection by a pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc) or by detecting the antibodies synthesised against the pathogen.

Question 12.
Enumerate the main sources of bio-fertilisers giving one example of each.
Answer:
Biofertilisers are organisms that enrich the nutrient quality of the soil.
The main sources of biofertilisers are bacteria, fungi and cyanobacteria.

1. The bacteria fix atmospheric nitrogen into organic forms, which are used by the plant as a nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (example, Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
2. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant. Plants having such associations show other benefits also, such as resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development.
3. In paddy fields, cyanobacteria serve as an important biofertiliser. Blue-green algae also add organic matter to the soil and increase its fertility.

Note
Biofertiliser can be defined as biological products containing living micro-organisms, that, when applied to seed, plant surfaces, or soil, promote growth by several mechanisms such as increasing, the supply of nutrients, increasing root biomass or root area & increasing nutrient uptake capacity of the plant.

Section – C

Question 13.
To save the crop plant from the attack of various insect pests the biotechnologists have developed many pest resistant plants. One such example is Bt com plant. In this plant ‘cry’ genes were introduced which produces cry- proteins in the plant that has toxic effect on the pest (corn borer). Thus saves the com plant from the attack of the corn borer. An experimental field study was conducted by the scientists to see the efficacy of the Bt corn plant against the attack of corn borers.

Three different species of corn borers namely ‘A’, ‘B’, ‘C’ were collected and were independently fed on non Bt com plants and Bt corn plants separately for the same period. The extent of the damage caused to the leaf area of the plant was observed and noted down. With the help of the observations and data collected the following bar graph was plotted. Study the graph and answer the questions that follow.

(i) Identify the species of the corn borer that was most successfully controlled by Bt corn plant. Give appropriate reason for your inference.
(ii) Identify the species of the corn borers which shows least impact of toxin produced by Bt genes.
(iii) What would be your advise as a Scientist, to the farmers for growing this particular Bt corn variety in the area which is infested by species-‘B’ of corn borers?
(iv) Name one Bt gene that encodes protein in com plants to control corn borers.

OR

A gene was identified in a fungus by a research worker in a lab which was considered to be of a great importance in the field of agriculture. As a student of biotechnolgy, write the steps you would suggest to
(i) Isolate this gene of interest from the fungus and
(ii) amplify this gene for further experimentation and research.
Answer:
(i) The species ‘A’ of the corn bore was most successfully controlled by the Bt corn plant. It is because cry gene is expressed in plants to provide resistance to insects. And show less damage in comparison to species B and C.

(ii) Species B shows very less impact of the Bt gene because the damage rate is almost equal in plant species of non-Bt crop and Bt crop.

(iii) The scientist we must give advice to farmer are —

• When different species of plants are cultivated on the same field, there is a definite distance between
  crops of the same species. So, it is efficient in attracting pests away from their target host plant.
• To manage pests, the crop rotation farming method also increases the fertility of the soil.
• Organic pesticides allow the farmers to turn agricultural outputs into natural pesticides and do not affect their health or damage the crops, like farmers can use Bacillus thuringiensis (bacteria) on their crops to reduce the effect of insects on the plant.

(iv) The cry gene protein is the Bt gene that encodes protein in corn plants.

OR

(i) Isolation of the Genetic Material (DNA)

To cut the DNA with restriction enzymes, it needs to be in pure form, free from other macro-molecules. Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA along with other macromolecules such as RNA, proteins, polysaceharides and also lipids. This can be achieved by treating the fungi with the enzymes chitinase.

The RNA can be removed by treatment with ribonuclease whereas proteins can be removed by
treatment with protease. Other molecules can be removed by appropriate treatments and purified DNA ultimately precipitates out after the addition of chilled ethanol. This can be seen as a collection of fine threads in the suspension.

(ii) Amplification of Gene of Interest using PCR

The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as a template. If the process of replication of DNA is repeated many times, the segment of DNA can be
amplified approximately a billion times, i.e., 1 billion copies are made.

The amplified fragment if desired can now be used to ligate with a vector for further cloning.

Note
Cry gene:
Cry proteins are encoded by cry genes, these prceins are protoxin, produced by bacteria Bacillus thuringiensis. These bacteria contain proteins in their inactive from, when these inactive protein in ingested by insect, it get activated by the alkaline pH of the gut.