CBSE Class 12 – Biology Question Paper 2022

SECTION A

1. Mention the parts of the human body that get affected by Pneumonia and common cold infections. Write the causative agents of the two diseases.
Answer:
Pneumonia primarily affects the lungs, causing inflammation and fluid buildup. The common cold typically affects the upper respiratory system, including the nose, throat, and sinuses.
The causative agents are:
Pneumonia: Bacteria (e.g., Streptococcus pneumoniae, Haemophilus influenzae) or viruses (e.g., influenza virus, respiratory syncytial virus).
Common cold: Viruses (e.g., rhinovirus, coronavirus).

2. State the impact of constant mechanical agitation and pumping of air in the aeration tank on the sewage during the biological treatment.
Answer:
The constant mechanical agitation and pumping of air in the aeration tank help to mix the sewage and provide oxygen to the microorganisms involved in the biological treatment process. This promotes the growth and activity of aerobic bacteria that break down organic pollutants, improving the efficiency of the treatment process and reducing harmful substances in the sewage.

(a) Cattle excreta is an important source for producing a domestic fuel. Name the fuel and write its main components.
Answer:
The fuel produced from cattle excreta is biogas. The main components of biogas are:
Methane (CH₄), Carbon dioxide (CO₂), and small amounts of hydrogen sulfide (H₂S), ammonia (NH₃), and water vapor.

(b) Write the biological process that is responsible for the production of this fuel.
Answer:
The biological process responsible for biogas production is anaerobic digestion. In this process, microorganisms break down organic matter (such as cattle excreta) in the absence of oxygen, resulting in the formation of biogas.

3. (a) Give an example of a viral biocontrol agent.
Answer:
An example of a viral biocontrol agent is the Nuclear Polyhedrosis Virus (NPV), which infects and kills caterpillars of certain pest species like the cotton bollworm.

(b) Why are they considered to be desirable when an ecologically sensitive area is being treated?
Answer:
Viral biocontrol agents are considered desirable in ecologically sensitive areas because they are species-specific, meaning they target only the pests without harming non-target organisms. Additionally, they are biodegradable and do not leave harmful residues in the environment, making them safer for both the ecosystem and human health.

4. What is the importance of female Anopheles mosquitoes in the life of a malarial parasite Plasmodium?
Answer:
Female Anopheles mosquitoes are crucial in the life cycle of the malarial parasite Plasmodium. They serve as the vector that transmits the parasite from one human to another. When an infected mosquito bites a person, it injects Plasmodium sporozoites into the bloodstream. These sporozoites travel to the liver, where they mature and reproduce, eventually entering the bloodstream again to infect red blood cells and cause malaria symptoms.

5.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?

Answer:(a) Carrying capacity in respect to Curve ‘B’ represents the maximum population size that a particular environment can sustainably support over a long period. It’s the point where population growth plateaus due to limited resources, increased competition, or other environmental pressures.

(b) Mention the action of possible natural forces that could have lead to curve ‘B’.

Answer:(b) Possible natural forces that could have led to curve ‘B’ include limited food, water, space/habitat; increased competition and predation; spread of diseases; and environmental changes like fires, floods, droughts, or temperature fluctuations.

6.The histogram given below representing the data for annual shark harvest in the great barrier reef / coral reef 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.

Answer:(a) Interpretation of the data: The histogram shows an increasing trend in annual shark harvest (catch in tonnes) in the Great Barrier Reef/Coral Sea region of Queensland, Australia, from 1992 to 2003. Catches were relatively lower in the early years (1992-1996), fluctuating between roughly 200 and 400 tonnes. From 1997 onwards, a noticeable increase is observed, with the highest catches in later years, particularly around 2000-2002, exceeding 800 and reaching over 1000 tonnes. This suggests a potential increase in shark fishing or improved data collection, but further context is needed for definitive conclusions.

(b) Write the impact on the biodiversity of the area that you can interpreton the basis of given data.

Answer;(b) Impact on Biodiversity: The increasing shark harvest data suggests potential negative impacts on the Great Barrier Reef ecosystem’s biodiversity. A likely decline in shark populations could occur if harvesting is unsustainable. As apex predators, a reduction in shark numbers can disrupt food webs, potentially increasing prey species and decreasing other species reliant on sharks. This can alter nutrient cycling, species composition, and overall ecosystem health. Intense fishing pressure can also reduce genetic diversity within shark populations, making them less resilient. While this data alone is insufficient for a complete assessment, the upward harvest trend raises concerns about overfishing and its potential consequences for the reef’s biodiversity.

“Stability of community depends upon its species richness.” How did David Tilman show this experimentally?

Answer:
David Tilman conducted a series of experiments to demonstrate the relationship between species richness and community stability. He set up long-term experiments using grassland ecosystems where different plots were seeded with varying numbers of plant species. His key findings were:

In these plots, he found that the communities with higher species richness were more stable in terms of biomass production over time, especially under varying environmental conditions such as drought or changes in nutrient availability.
The experimental results showed that communities with more species were more resistant to disturbances (like droughts) and could recover more quickly. This was because different species have different ecological roles, and a diverse community has a greater chance of maintaining ecosystem functions even if some species are affected by disturbances.

Tilman’s work provided strong evidence that species richness enhances the stability of ecosystems by promoting functional redundancy, where multiple species can perform similar roles, allowing the community to better withstand environmental stresses.

SECTION B

7.The data collected based on the survey conducted for species richness of group of mammals, in three different climatic regions of the world is shown in the bar graph given below.
Panama has nearly 560 species of mammals, Canada has nearly 301 species of mammals and Denmark has 67 species of mammals.

(i) Based on the species, richness, identify the location of these countries in the respective climatic regions given.

(i) Location of countries based on species richness: Panama (560 species) is located in the Tropical region. Canada (301 species) is located in the Temperate region. Denmark (67 species) is located in the Polar (North) region.

(ii) Plants and animals do not have a uniform diversity in the world. Write
the term given to this pattern of diversity and why?
(ii) Term for non-uniform diversity and reason: The term is Latitudinal Diversity Gradient. The primary reason is the variation in solar energy and climate across the globe. Tropics receive more direct sunlight, leading to warmer temperatures, higher humidity, and stable climate, fostering high biodiversity. Temperate regions receive less solar energy and have distinct seasons, resulting in lower diversity. Polar regions receive the least solar energy and have extremely cold conditions, limiting the number of surviving species and resulting in very low biodiversity. Other factors include evolutionary history, habitat complexity, and productivity.

8.(a) How many episodes of mass extinctions of species have already taken place and which one is in progress in the current era?
Answer:
There have been five major mass extinction events in Earth’s history, often referred to as “The Big Five.” The current extinction event in progress is called the Sixth Mass Extinction, which is largely driven by human activities such as habitat destruction, climate change, pollution, and over-exploitation of species.

(b) How is the current episode in progress different from the previous episodes and why? Explain.
Answer:
The current Sixth Mass Extinction differs from previous events because it is primarily caused by human activities rather than natural phenomena like volcanic eruptions or asteroid impacts. Human-induced factors, such as deforestation, global warming, habitat fragmentation, and the introduction of invasive species, are accelerating the loss of biodiversity at a rate much faster than in previous extinction events. This anthropogenic impact is unprecedented, and many species are being lost before they are even fully discovered.

9.Name two naturally occurring sources, one that transfers pathogenic genes into plant cells and the other into animal cells respectively, for their benefit. Write how have these naturally occurring sources been used for the benefit of the human race by the biotechnologists.
Answer:
For plant cells, Agrobacterium tumefaciens is a bacterium that transfers pathogenic genes into plant cells, causing crown gall disease in plants. Biotechnologists have utilized this ability to insert beneficial genes into plants for genetic modification, such as creating genetically modified crops that are pest-resistant or have enhanced nutritional qualities.
For animal cells, the Human Immunodeficiency Virus (HIV) can transfer genes into animal cells. Although HIV is pathogenic, its ability to insert its genetic material into host cells has been utilized in gene therapy, where scientists use viral vectors to deliver therapeutic genes into human cells to treat genetic disorders like cystic fibrosis or muscular dystrophy.
These naturally occurring sources have been used to improve agricultural productivity and develop medical treatments through genetic engineering and gene therapy.

10.Enumerate the main sources of bio-fertilizers giving one example of each.
Answer:
The main sources of bio-fertilizers are bacteria, fungi, and algae.
An example of a bacterial bio-fertilizer is Rhizobium, which forms symbiotic relationships with legume plants and fixes nitrogen from the atmosphere into a form that plants can use.
An example of a fungal bio-fertilizer is Mycorrhizal fungi, which forms symbiotic associations with plant roots, enhancing nutrient and water uptake, especially phosphorus.
An example of an algal bio-fertilizer is Blue-green algae (e.g., Anabaena), which can fix nitrogen and improve soil fertility.
These bio-fertilizers are eco-friendly alternatives to chemical fertilizers and help maintain sustainable agricultural practices.

11. Explain giving reason the action plan followed by organic farmers that support their key belief “biodiversity furthers health of crop lands.”
Answer:
Organic farmers believe that biodiversity plays a crucial role in maintaining the health of crop lands because it promotes a balanced ecosystem that can naturally control pests, diseases, and soil degradation. Organic farming encourages the use of a variety of plants, animals, and beneficial microorganisms in the farming system. This diversity strengthens ecosystem resilience by fostering natural predators, pollinators, and soil microorganisms, which enhance soil fertility and reduce the need for chemical fertilizers and pesticides. By maintaining a biodiverse environment, organic farmers reduce dependency on external inputs, prevent the build-up of pests and diseases, and ensure sustainable land use, ultimately supporting the long-term health and productivity of the soil.

12.(1) State the role of a selectable marker in r-DNA technology.
Answer:
In recombinant DNA (r-DNA) technology, a selectable marker is a gene introduced into the host organism that allows researchers to identify and select cells that have successfully taken up the recombinant DNA. This marker typically provides resistance to a specific antibiotic or a detectable trait that can easily distinguish transformed cells from non-transformed ones.

(ii) Name one such selectable marker which is considered to be useful for E.coli.
Answer:
One useful selectable marker for E. coli is the ampicillin resistance gene (bla). This gene allows transformed E. coli cells to grow in the presence of ampicillin, which would normally inhibit the growth of non-transformed cells.

(iii) Give one reason why is it considered to be a useful marker.
Answer:
The ampicillin resistance gene is considered a useful marker because it enables easy identification of transformed E. coli cells. Only the cells that have successfully incorporated the recombinant DNA and the ampicillin resistance gene will survive and proliferate in the presence of ampicillin, simplifying the selection process.

OR
What are plasmids? How are they different from cloning vectors? Give one example each for a viral and a bacterial cloning vector.
Answer:
Plasmids are small, circular DNA molecules that exist independently of the chromosomal DNA in bacteria and some other organisms. They can replicate autonomously and often carry genes that confer beneficial traits, such as antibiotic resistance.

Cloning vectors are modified plasmids or other DNA molecules used to carry foreign DNA into a host cell for replication and expression. The primary difference between plasmids and cloning vectors is that cloning vectors are specifically engineered to have features that facilitate the insertion, selection, and maintenance of foreign DNA. Plasmids can be used as cloning vectors, but not all plasmids are designed to be cloning vectors.

An example of a viral cloning vector is the bacteriophage lambda.
An example of a bacterial cloning vector is the pUC19 plasmid.

SECTION – C

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 corn 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 corn 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 corn 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.

Answer:(i) Species C was most successfully controlled by the Bt corn. The graph shows the lowest percentage of leaf area damage for species C on Bt corn compared to both its own damage on non-Bt corn and the damage caused by the other species on Bt corn.

(ii) Identify the species of the corn borers which shows least impact of toxin produced by Bt genes.

Answer;(ii) Species B shows the least impact of the Bt toxin. While the Bt corn did reduce damage caused by species B compared to non-Bt corn, the reduction is less significant than for species A and C.

(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?

Answer:(iii) If the primary goal is to protect the current crop, I would NOT recommend this Bt corn variety for areas heavily infested with species B. If species B is the dominant pest, research and development of a Bt corn variety specifically targeting species B is crucial.

(iv) Name one Bt gene that encodes protein in corn plants to control corn
borers.

Answer:(iv) cry1Ab or cry1Ac are common examples of Bt genes that encode for proteins (Cry proteins) effective against 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 biotechnology, 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) Steps to Isolate the Gene of Interest from the Fungus:

DNA Extraction:
The first step is to extract the genomic DNA from the fungus. This is done by breaking the fungal cell wall using enzymatic or mechanical methods, followed by a chemical process to isolate the DNA from other cellular components. The DNA is then purified to remove contaminants such as proteins and RNA.
Gene Identification:
If the gene of interest is already known, specific primers can be designed to target that gene. If the gene is unknown, bioinformatics tools or RNA sequencing can be used to identify the gene based on its function or similarity to known genes. This helps to locate the gene in the genomic DNA.
Polymerase Chain Reaction (PCR):
PCR is used to selectively amplify the gene of interest. First, primers specific to the gene are designed. The DNA is then mixed with these primers, nucleotides, and a heat-stable DNA polymerase in a reaction mixture. Through repeated cycles of denaturation, annealing, and extension, the gene is amplified.
Gel Electrophoresis:
After PCR, the amplified gene is analyzed by gel electrophoresis. This technique separates the PCR products based on size, allowing researchers to confirm that the gene of interest has been successfully amplified. The gene should appear as a distinct band at the expected size.
Purification:
The amplified gene is then purified from the gel using a gel extraction kit. This step ensures that only the gene of interest remains, free of any unwanted DNA fragments.

(ii) Steps to Amplify the Gene for Further Experimentation and Research:

Cloning into a Vector:
After isolating the gene of interest, it is inserted into a suitable cloning vector (like a plasmid). The plasmid is chosen to ensure it has features like antibiotic resistance genes and an origin of replication. The gene and the plasmid are both digested with specific restriction enzymes that create compatible ends for ligation.
Ligation:
The purified gene of interest is then ligated into the plasmid vector using DNA ligase. This enzyme facilitates the joining of the gene to the plasmid, creating a recombinant plasmid containing the gene of interest.
Transformation:
The recombinant plasmid is introduced into a host cell, typically E. coli, through a process called transformation. This can be achieved by methods like heat shock or electroporation. The host cells take up the recombinant plasmid and replicate it.
Selection:
The transformed cells are plated on selective media that contain an antibiotic, such as ampicillin. Only the cells that have successfully incorporated the plasmid (which contains the antibiotic resistance gene) will survive and grow.
Colony PCR/Restriction Digest:
To confirm that the plasmid contains the gene of interest, researchers can perform colony PCR or a restriction digest, followed by gel electrophoresis. This allows them to verify that the plasmid has the correct insert.
Amplification and Purification:
Once the correct colony is identified, it is grown in a culture, and the recombinant plasmid is isolated using plasmid purification techniques. The purified plasmid can then be used for further experiments and research, such as gene expression studies, protein production, or functional analysis.