CBSE Class 12 – Biotechnology Question Paper 2022

SECTION A

1. Construct a flowchart showing the action of t-PA (tissue plasminogen activator).

Answer: A flowchart representing the action of t-PA:

  1. t-PA (tissue plasminogen activator) is released by endothelial cells in response to injury.
  2. t-PA binds to fibrin in the clot.
  3. t-PA activates plasminogen to plasmin.
  4. Plasmin breaks down fibrin, dissolving the clot.
  5. The clot dissolves, restoring normal blood flow.

2. Why can foaming cause problems in microbiological processes?

Answer: Foaming can cause problems in microbiological processes because:

  1. Reduced efficiency: Foam can hinder proper aeration, leading to poor oxygen transfer.
  2. Contamination risk: Foam can lead to spills and contamination in the process.
  3. Difficult monitoring: Foam may obscure the accurate monitoring of culture conditions (e.g., pH, temperature).
  4. Damage to equipment: Foam buildup can damage bioreactor equipment or overflow vessels.

3. What information can be obtained from the following Database retrieval tools?

(a) Locus link

Answer: LocusLink provides detailed information about gene loci, including gene sequence, associated disorders, and functional annotations.

(b) Taxonomy browser

Answer: The Taxonomy browser offers a hierarchical classification of species, allowing users to explore genetic and taxonomic information of different organisms.

4. (a) Ripening of fruits has been slowed down to prevent their spoilage during transportation. How?

Answer: Fruit ripening is slowed by controlling:

  1. Temperature: Lower temperatures reduce the activity of ripening hormones (ethylene).
  2. Ethylene inhibitors: Use of ethylene gas blockers, like 1-MCP (1-methylcyclopropene), delays ripening.
  3. Controlled atmosphere storage: Altering oxygen and carbon dioxide levels reduces respiration rates, slowing ripening.

OR

(b) Plants have adapted to cope with abiotic stress conditions. How?

Answer: Plants adapt to abiotic stress through mechanisms like:

  1. Drought resistance: Developing deep roots and closing stomata to conserve water.
  2. Salt tolerance: Accumulating osmolytes or using specialized proteins to manage salt stress.
  3. Temperature tolerance: Producing heat shock proteins or altering membrane lipids to maintain cellular integrity under stress.

5.(a) What is ‘Golden Rice’? How is it developed?

Answer: Golden Rice is a genetically modified rice that has been engineered to produce beta-carotene, a precursor of vitamin A, in the edible parts of the rice. It was developed to help address vitamin A deficiency in developing countries, where rice is a staple food, but vitamin A deficiency is common.

Development of Golden Rice:

  1. Gene selection: The genes responsible for the production of beta-carotene were identified. These include genes from the daffodil plant (daffodil phytoene synthase) and a bacterium (Erwinia uredovora phytoene desaturase).
  2. Gene insertion: These genes were inserted into the rice genome using techniques such as Agrobacterium-mediated transformation or particle bombardment (gene gun).
  3. Expression: The inserted genes express beta-carotene in the rice grains, specifically in the endosperm, which is the edible part of the rice.

Golden Rice has the potential to help reduce vitamin A deficiency, which can cause blindness and other health issues, especially in children.

5.(b) What are Cybrids? Name any two cytoplasmic traits that can be transferred using Cybrids, from one plant species to another.

Answer: Cybrids (cytoplasmic hybrids) are hybrids created by fusing cells from different species, where the nuclear material comes from one species, and the cytoplasm (which includes mitochondria and plastids) comes from another. This allows the transfer of cytoplasmic traits from one species to another without altering the nuclear genome.

Two cytoplasmic traits that can be transferred using Cybrids:

  1. Mitochondrial function: Cybrids can transfer traits related to mitochondrial efficiency, including the ability to handle oxidative stress or improve ATP production.
  2. Chloroplast function: Cytoplasmic hybrids can transfer traits like photosynthetic efficiency, which may improve plant growth and productivity.

Cybrids are valuable for plant breeding and biotechnology as they allow the exchange of cytoplasmic features without changing the nuclear genetic material of the plants.

SECTION B

7. (a) Why is regulation of pH important for survival of mammalian cells in culture? Write two reasons.

Answer:

  1. Enzyme activity: Enzymes in cells have optimal pH ranges for proper function, and deviations can reduce their activity.
  2. Ion balance: pH affects the ionization of molecules, influencing cellular processes like nutrient uptake and protein function.

(b) How does bicarbonate CO₂ buffering system work?

Answer: The bicarbonate-CO₂ buffering system helps maintain pH stability by balancing the concentration of CO₂ and bicarbonate (HCO₃⁻) in the culture medium. When pH decreases (becomes more acidic), CO₂ dissolves in water to form carbonic acid, which dissociates to release H⁺ ions. The bicarbonate absorbs excess H⁺, neutralizing the change in pH.

8. What is RefSeq? Give its significance. (Any 2 points)

Answer: RefSeq (Reference Sequence) is a curated collection of genomic sequences from multiple organisms.

Significance:

  1. Gene annotation: RefSeq provides a reference for annotating genes and other functional elements in genomes.
  2. Research consistency: It enables researchers to standardize the comparison of gene sequences across different studies, aiding in data analysis and interpretation.

9. (a) A medium for microbial culture contains components like peptone, meat extract, yeast extract, casein digest, and corn steep liquor. This culture medium is a complex medium. Why?

Answer: This culture medium is classified as a complex medium because it contains natural sources like peptone, yeast extract, and meat extract, which are not chemically defined. The exact composition and concentration of nutrients in these ingredients are not precisely known, making the medium complex. It provides a broad range of nutrients to support the growth of various microorganisms.

9. (b) Why is agar added to any nutrient medium?

Answer: Agar is added to nutrient media because it serves as a solidifying agent. It is a polysaccharide extracted from seaweed that remains solid at body temperature and provides a firm surface for growing microorganisms. This allows the growth of distinct colonies, making it easier to isolate and identify microorganisms.

9. (c) What are the conditions for sterilization of culture medium in an autoclave?

Answer: The sterilization conditions in an autoclave typically involve:

  1. Temperature: 121°C (250°F)
  2. Pressure: 15-20 psi (pounds per square inch)
  3. Time: 15-20 minutes, depending on the volume of the medium. These conditions ensure the destruction of microbial life, including bacterial spores, ensuring the medium is sterile and safe for microbial growth.

10. (a) Animal cell cultures are placed in CO2 incubators, as they help to reproduce environmental conditions close to the living cells. How?

Answer: CO₂ incubators create optimal environmental conditions for animal cell cultures by maintaining:

  1. Temperature: Usually around 37°C, which is the normal body temperature of most animals.
  2. CO₂ concentration: A steady level of 5% CO₂ is maintained to help buffer the medium’s pH. This mimics the conditions found in the body where CO₂ is produced during cellular metabolism.
  3. Humidity: The incubator also provides a humidified environment to prevent dehydration of cells and culture medium.

Together, these conditions help the cells to grow and function in a way that is similar to the conditions in the living organism.

10. (b) “Serum is an important component of animal cell culture.” Support the statement giving two reasons. Why are antibiotics added to culture medium?

Answer: Serum is important for animal cell culture for the following reasons:

  1. Growth factors: Serum provides essential growth factors, hormones, and proteins that promote cell division and survival.
  2. Nutrients: Serum is rich in essential nutrients like amino acids, vitamins, and lipids that support cellular metabolism.

Antibiotics are added to culture media to prevent bacterial contamination. They help to inhibit the growth of unwanted microorganisms without affecting the cultured animal cells.

How can a farmer eliminate the process of emasculation to prevent unnecessary pollination in his maize crop? Can normal pollen formation be ensured at the onset of breeding seasons?

Answer: To eliminate the process of emasculation and prevent unnecessary pollination in maize crops, a farmer can use genetic male sterility (GMS). This involves using maize varieties that have been genetically modified to prevent pollen formation. These sterile male plants are unable to produce viable pollen, thus preventing unwanted pollination.

At the onset of the breeding season, controlled pollination can be ensured by using male sterile plants alongside female fertile plants, allowing controlled hybridization without manual emasculation.

Draw a labelled diagram of an artificial seed. Why are these seeds produced?

Answer: An artificial seed is a technique used to encapsulate plant tissue (like somatic embryos) in a gel-like material, mimicking the structure of a natural seed. The encapsulation material is often agar or a similar substance, which provides protection and nutrients for the tissue to grow.

Why are artificial seeds produced?

  1. Clonal propagation: Artificial seeds allow the production of genetically identical plants, particularly for crops with difficult propagation methods.
  2. Storage and transport: They provide a more manageable and durable form of plant tissue, which can be stored and transported for later planting.
  3. Increased efficiency: Artificial seeds improve the efficiency of plant breeding and restoration programs.

For Visually Impaired Candidates Only What are artificial seeds? Why are they produced?

Answer: Artificial seeds are a form of plant propagation created by encapsulating somatic embryos or other plant tissues in a protective coating. This coating mimics the seed’s natural structure and provides a suitable environment for germination.

Why are they produced?

  • To propagate plants clonally without the need for seeds.
  • To improve transportation and storage of plant material for later use or distribution.
  • To aid in plant conservation or restoration programs by providing an easy-to-handle form of plant tissue.

SECTION C

13. (a) Microbial Cultures:

Microbial cultures have immense potential for production of useful compounds, including enzymes, steroids, antibiotics, therapeutic proteins, microbial leaching, and biodegradable waste treatment.

(i) Give an example where microbial metabolism has been used to convert unsuitable substrates to useful products.

Answer: An example is the conversion of cellulose (a complex, indigestible substrate for many organisms) into ethanol by using certain microbes such as Saccharomyces cerevisiae. This process is used in biofuel production, converting plant biomass into a usable fuel.

(ii) Define DSP. Why is it advisable to use fewer steps in a DSP protocol?

Answer: DSP (Downstream Processing) refers to the purification and recovery of products from a fermentation process. This typically involves the separation of the desired product from the culture medium and other by-products.

It is advisable to use fewer steps in DSP to:

  • Reduce cost: Each step in the DSP process incurs additional costs.
  • Improve yield: Fewer steps minimize the risk of product loss during processing.

(iii) What are excipients?

Answer: Excipients are inactive substances used in the formulation of a drug or therapeutic product. They serve as fillers, binders, or stabilizers, helping to deliver the active ingredient in an effective form.

(iv) Which organisms are referred to as GRAS?

Answer: GRAS (Generally Recognized As Safe) refers to microorganisms or substances that are considered safe for consumption or use in food and pharmaceuticals based on established scientific evidence. Examples include Saccharomyces cerevisiae (baker’s yeast) and Lactobacillus species used in yogurt production.

(v) Briefly mention two biosafety issues specific in microbial technology.

Answer:

  1. Containment of genetically modified organisms (GMOs): There is a risk of GMOs escaping into the environment, potentially disrupting ecosystems or causing unintended consequences.
  2. Pathogen risk: Microbial cultures, especially pathogenic strains, can pose health risks to researchers or the public if proper safety protocols are not followed.

OR

(b) Continuous Culture :
To get a continuous supply of microbial growth, continuous culture
is used. The growth medium is designed in such a way that one of
the nutrients is in limited quantity. Nutrients are continually
added to the bioreactor and spent culture broth is removed at the
same time. This culture helps to obtain stable product quality and
higher productivity per unit volume, so this technique is widely
used for production of both microbial biomass as well as their
metabolites.

(i) Turbidostat vs. Chemostat:

Turbidostats control culture turbidity by adjusting media flow rate, while chemostats maintain a constant limiting nutrient concentration to control growth rate. Turbidostats use a turbidity sensor for feedback, whereas chemostats rely on a pre-set nutrient concentration in the media reservoir. Growth rate is indirectly controlled in turbidostats via turbidity, and directly controlled in chemostats by dilution rate. Cell density is maintained at a specific level in turbidostats, but varies with nutrient concentration in chemostats.

(ii) Culture Type and Batch Culture:

The graph shows a continuous culture, characterized by steady-state concentrations of cells, substrate, and potentially a secondary substrate or product. Batch culture is a closed system where all nutrients are provided initially, and no additions or removals occur during cultivation. The culture progresses through lag, exponential, stationary, and decline phases as conditions change within the vessel.

(iii) Continuous vs. Fed-Batch Culture:

Continuous cultures maintain a constant volume by balancing media inflow and outflow, whereas fed-batch cultures experience increasing volume due to nutrient addition without outflow until the process ends. Continuous culture is preferred for extended log or stationary phases due to stable nutrient and waste levels. Fed-batch can extend the log phase with controlled nutrient addition, but it’s less dynamically stable than continuous systems.

(For Visually Impaired Candidates Only in lieu (ii))