Section 12 — Solved Examples
This is the dedicated problem set for Chapter 10 (Biotechnology and Its Applications). The 30 worked examples below are arranged in three tiers — concept checks (definitions and key terms), application and scenarios (case-style situations on Bt crops, insulin, gene therapy and diagnosis), and analytical and multi-concept (reasoning problems that link agriculture, medicine and ethics across the whole chapter).
Unlike a plain glossary, most of these ask you to identify, explain and justify, because that is how an applications question earns marks in a Board or entrance paper. Naming the technique is rarely enough; you are usually asked why it works, how the molecule behaves, or what the outcome means for a farmer or a patient.
How to use this section
- Concept Checks (Q1-Q10): Quick recall of definitions and named facts. If you stumble on more than one or two, revisit Sections 2-11.
- Application and Scenarios (Q11-Q20): The workhorse 2- and 3-mark questions — Bt mechanism, RNAi, insulin production, gene therapy, molecular diagnosis and transgenic animals.
- Analytical and Multi-Concept (Q21-Q30): Multi-step reasoning that ties several topics together, the kind that separates a good answer from a full-mark answer.
Total target time: around an hour for a complete revision sweep.
Note: This section is for practice and revision only — there is no quiz at the end. Treat each answer as a model of how much detail an examiner expects.
Memory Capsule — Facts Worth Locking In
Before working through the problems, fix these ten high-yield facts firmly in mind:
| # | Fact | Where it is tested |
|---|---|---|
| 1 | Totipotency = capacity of a cell/explant to grow into a whole plant; micropropagation gives genetically identical somaclones | Tissue culture |
| 2 | Meristem (apical and axillary) stays virus-free even in an infected plant — cultured in banana, sugarcane, potato | Virus-free plants |
| 3 | Somatic hybridisation fuses naked protoplasts of two varieties; tomato + potato gave the pomato, which lacked commercial traits | Protoplast fusion |
| 4 | Golden rice = vitamin-A-enriched rice; GM crops resist abiotic stress and pests, cut post-harvest loss | GM crops |
| 5 | Bt toxin from Bacillus thuringiensis; inactive protoxin activated by alkaline insect gut; coded by cry genes | Bt crops |
| 6 | cryIAc and cryIIAb control cotton bollworms; cryIAb controls corn borer | cry gene matching |
| 7 | RNAi silences a specific mRNA using a complementary dsRNA; used against the nematode Meloidogyne incognita in tobacco | RNA interference |
| 8 | Eli Lilly (1983) made insulin chains A and B separately in E. coli, then joined them by disulphide bonds; C peptide absent in mature insulin | Insulin |
| 9 | First gene therapy (1990), a 4-year-old girl with ADA deficiency; functional ADA cDNA via a retroviral vector | Gene therapy |
| 10 | Molecular diagnosis: PCR amplifies nucleic acid (HIV, cancer mutations); ELISA uses antigen-antibody interaction | Diagnosis |
Pro tip: For most applications questions, three things earn marks — the technique or organism, the molecular mechanism, and the practical benefit or example. Cover all three even when only one is asked.
Concept Checks (Q1-Q10)
Q1. Define totipotency and name the process that uses it to raise thousands of plants.
Answer: Totipotency is the capacity of a single cell or explant to generate a whole plant. The process that exploits it to produce thousands of plants in a short duration through tissue culture is called micropropagation. Each plant so produced is genetically identical to the parent and is termed a somaclone.
Q2. What is an explant, and what must the nutrient medium supply for it to grow?
Answer: An explant is any part of a plant taken out and grown in a test tube under sterile conditions. The medium must supply a carbon source such as sucrose, along with inorganic salts, vitamins, amino acids and growth regulators (auxins and cytokinins) that steer it towards forming roots, shoots and a complete plantlet.
Q3. Why can a virus-free plant be raised from a virus-infected plant, and name three plants done this way.
Answer: Even in an infected plant the meristem (apical and axillary) remains free of the virus. Removing the meristem and growing it in vitro therefore yields virus-free plants. This has been done successfully for banana, sugarcane and potato.
Q4. What is a Genetically Modified Organism, and name a GM crop with enhanced nutrition.
Answer: A Genetically Modified Organism (GMO) is a plant, bacterium, fungus or animal whose genes have been altered by manipulation. A well-known GM crop with enhanced nutrition is golden rice, a variety enriched with vitamin A to combat vitamin-A deficiency.
Q5. Which organism produces the Bt toxin, and in what form does the bacterium store it?
Answer: The Bt toxin is produced by the soil bacterium Bacillus thuringiensis. The bacterium stores it as protein crystals containing an inactive protoxin, which is why the toxin does not harm the bacterium that makes it.
Q6. Which cry genes control cotton bollworms, and which controls the corn borer?
Answer: The proteins encoded by cryIAc and cryIIAb control the cotton bollworms, while cryIAb controls the corn borer. The correct cry gene must be matched to the crop and its particular pest.
Q7. In which organisms does RNA interference occur, and what does it silence?
Answer: RNA interference (RNAi) occurs in all eukaryotic organisms as a method of cellular defence. It silences a specific mRNA through a complementary double-stranded RNA (dsRNA) that binds the message and prevents its translation.
Q8. Describe the structure of the insulin molecule.
Answer: Insulin consists of two short polypeptide chains — chain A and chain B — linked together by disulphide bridges. It is first made as a pro-hormone carrying an extra C peptide, which is removed during maturation and is absent from the finished hormone.
Q9. To whom was the first clinical gene therapy given, and for what disorder?
Answer: The first clinical gene therapy was given in 1990 to a 4-year-old girl suffering from adenosine deaminase (ADA) deficiency, a disorder caused by the deletion of the gene for adenosine deaminase, an enzyme crucial for the immune system.
Q10. Define a transgenic animal, and state which animal makes up most of them.
Answer: A transgenic animal is one whose DNA has been manipulated so that it possesses and expresses an extra (foreign) gene. Although rats, rabbits, pigs, sheep, cows and fish have all been produced, over 95 per cent of transgenic animals are mice, valued for their short life cycle and well-mapped genetics.
Application and Scenarios (Q11-Q20)
Q11. A gardener wants many identical copies of one elite banana plant, all free of a virus that infects the parent. Outline the two tissue-culture ideas that make this possible.
Answer: First, micropropagation multiplies a single elite plant into thousands of genetically identical somaclones in a short time under sterile conditions. Second, because the meristem stays virus-free even in an infected plant, the gardener can excise the meristem and grow it in vitro to obtain virus-free stock. Combining the two gives many uniform, healthy, virus-free banana plants — which is exactly why banana is a standard example of both techniques.
Q12. Two plant varieties, each with a useful trait, cannot be crossed sexually. How can their traits still be combined in one cell, and what was the classic result?
Answer: Their cell walls are digested to leave naked protoplasts, and protoplasts from the two varieties are then fused to form a hybrid protoplast, which is grown into a somatic hybrid — a process called somatic hybridisation that bypasses sexual reproduction. The classic result was the fusion of tomato and potato protoplasts to give the pomato, though it did not carry all the characters needed to be commercially useful.
Q13. The nematode Meloidogyne incognita is ruining a tobacco crop by attacking the roots. Explain the pesticide-free strategy used to protect the plant.
Answer: The strategy uses RNA interference. Agrobacterium vectors introduce nematode-specific genes arranged so that the host cells produce both sense and anti-sense RNA. Being complementary, these pair into a double-stranded RNA (dsRNA) that triggers RNAi and silences the specific mRNA of the nematode. With its essential message switched off, the parasite cannot survive in the transgenic plant, so the crop is protected without any pesticide.
Q14. A company wants to make human insulin in bacteria. Describe how Eli Lilly achieved this in 1983.
Answer: In 1983 Eli Lilly prepared two DNA sequences corresponding to chain A and chain B of human insulin and introduced them into plasmids of E. coli to be produced separately. The two chains were then extracted and combined by creating the disulphide bonds between them to form mature human insulin. Because the product matches the human protein, it avoids the immune problems of animal-derived insulin.
Q15. Explain why insulin cannot be taken as a tablet and why insulin from slaughtered animals caused problems.
Answer: Insulin is a protein, so if swallowed it would be digested in the gut before it could act — hence it is injected. Before recombinant methods, insulin was extracted from the pancreas of slaughtered cattle and pigs; being a foreign animal protein, it sometimes caused allergy or other immune reactions in patients. Recombinant human insulin solves both the source and the immune problem.
Q16. Describe the gene-therapy procedure used for the ADA-deficient child and explain why it was not a permanent cure.
Answer: Lymphocytes from the patient's blood were grown in culture, a functional ADA cDNA carried by a retroviral vector was introduced into them, and the corrected cells were returned to the patient, where they made the missing enzyme. It was not permanent because these lymphocytes are not immortal, so the patient needs periodic infusions. If the gene isolated from marrow cells producing ADA is introduced into cells at early embryonic stages, it could be a permanent cure.
Q17. A clinician wants to detect an infection long before symptoms appear. Which molecular technique fits, and how does it work?
Answer: PCR (Polymerase Chain Reaction) fits, because a pathogen is normally suspected only after symptoms appear, when its concentration is already high. PCR detects very low concentrations of a bacterium or virus by amplifying its nucleic acid — making millions of copies until there is enough to detect. In routine use it is applied to detect HIV in suspected AIDS patients and mutations in suspected cancer patients, as well as many genetic disorders.
Q18. On what principle does ELISA work, and what two signals can it pick up to confirm an infection?
Answer: ELISA works on the principle of antigen-antibody interaction. It can confirm an infection in one of two ways: by detecting the antigens of the pathogen itself, such as its proteins and glycoproteins, or by detecting the antibodies the patient's own immune system has synthesised against that pathogen. Either signal shows the infection is present.
Q19. What was Rosie, why was she significant, and name another product transgenic animals can make cheaply.
Answer: Rosie, produced in 1997, was the first transgenic cow. She gave human-protein-enriched milk containing human alpha-lactalbumin at 2.4 grams per litre, nutritionally more balanced for human babies than natural cow milk. Transgenic animals can also make costly medical proteins cheaply — for example alpha-1-antitrypsin, used to treat emphysema.
Q20. A policymaker asks how GM crops help both the farmer and the wider public. Summarise the main benefits.
Answer: GM crops make plants more tolerant to abiotic stresses such as cold, drought, salt and heat; make them pest-resistant, cutting reliance on chemical pesticides; reduce post-harvest losses; and increase the efficiency of mineral use, which prevents early exhaustion of soil fertility. They also enhance nutritional value — golden rice being the flagship example — and yield tailor-made plants that supply industry with starches, fuels and pharmaceuticals.
Analytical and Multi-Concept (Q21-Q30)
Q21. Explain fully why the Bt protoxin is safe inside the bacterium yet lethal once an insect eats it, tracing the toxin from crystal to insect death.
Answer: Inside Bacillus thuringiensis the toxin exists as an inactive protoxin packed in protein crystals, so it cannot harm the bacterium. When an insect ingests the crystals, the alkaline pH of the insect gut solubilises them and converts the protoxin into the active toxin — a switch that happens only inside the pest. The activated toxin then binds the surface of the midgut epithelial cells, creates pores in their membranes, and makes the cells swell and burst (lysis), so the insect dies. Safety in the bacterium and lethality in the insect both stem from the same protoxin-to-toxin switch.
Q22. Compare micropropagation and somatic hybridisation as ways of producing new plants, noting what each can and cannot achieve.
Answer: Micropropagation produces a large number of plants that are genetically identical somaclones of a single parent; it gives speed, uniformity and scale but cannot introduce a new trait — the copies are only as good as the original. Somatic hybridisation instead fuses naked protoplasts of two different varieties to blend their traits in a somatic hybrid, achieving combinations impossible by sexual crossing. Its limitation is that the outcome may not be commercially useful, as the pomato showed. In short, micropropagation multiplies an existing genotype, while somatic hybridisation tries to create a new one.
Q23. RNAi is described as turning the plant into its own guardian. Justify this, and state where in nature the triggering RNA normally comes from.
Answer: The plant is engineered with nematode-specific genes so that it makes sense and anti-sense RNA that pair into a dsRNA; this dsRNA initiates RNAi and silences the parasite's own essential mRNA, not any plant gene. The nematode therefore cannot survive on the transgenic host, so the plant defends itself without external pesticide — hence its own guardian. In nature the complementary RNA that triggers RNAi comes from viruses with RNA genomes or from mobile genetic elements (transposons) that replicate through an RNA intermediate.
Q24. Trace the maturation of insulin from pro-hormone to functional hormone, and explain why this detail made the recombinant product tricky to assemble.
Answer: In mammals insulin is first made as a pro-hormone containing chains A and B plus an extra C peptide. During maturation the C peptide is removed, and the remaining chains A and B are linked by disulphide bridges to give the functional hormone. This made the recombinant version tricky because the challenge was to obtain insulin correctly assembled into its mature two-chain form. Eli Lilly solved it by producing chains A and B separately in E. coli and then joining them through disulphide bonds rather than trying to reproduce the natural processing of the C peptide.
Q25. For ADA deficiency, compare bone marrow transplantation, enzyme replacement and gene therapy, and explain what a truly permanent cure would require.
Answer: Bone marrow transplantation can help but depends on a suitable donor; enzyme replacement therapy supplies functional ADA by injection but must be repeated because it does not restore the body's own ability to make the enzyme; neither is completely curative. Gene therapy introduces a functional ADA cDNA via a retroviral vector into the patient's cultured lymphocytes, which then make the enzyme — but as these cells are not immortal, periodic infusions are needed. A permanent cure would require introducing the functional ADA gene from marrow cells at early embryonic stages, so the correction is lifelong.
Q26. A suspected cancer patient and a suspected AIDS patient both need molecular diagnosis. Explain how a radioactive probe and PCR each reveal disease, and how their read-outs differ.
Answer: With the probe method, a single-stranded DNA or RNA tagged with a radioactive molecule is allowed to hybridise to complementary DNA in a clone of cells, read by autoradiography. A clone carrying a mutated gene will not appear on the film, because the probe is no longer complementary and cannot bind — absence of a signal flags the mutation. PCR instead amplifies the pathogen's nucleic acid so that even a very low concentration becomes detectable; it is used to detect HIV in suspected AIDS patients and gene mutations in suspected cancer patients. One relies on a missing signal, the other on multiplying a tiny signal until it is unmistakable.
Q27. Set out the five main uses of transgenic animals, giving one concrete example for each.
Answer: (1) Normal physiology and development — studying how genes are regulated, e.g. insulin-like growth factor. (2) Study of disease — models for cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer's to test new treatments. (3) Biological products — making costly proteins cheaply, e.g. alpha-1-antitrypsin for emphysema, and Rosie's milk with human alpha-lactalbumin. (4) Vaccine safety — transgenic mice testing the polio vaccine, possibly replacing monkeys. (5) Chemical (toxicity) safety testing — animals made more sensitive to toxins give results in less time.
Q28. Golden rice and tailor-made industrial plants are both cited as triumphs of GM technology. Explain how each addresses a different kind of human need.
Answer: Golden rice addresses a nutritional and health need: it is rice enriched with vitamin A, developed for populations that depend on rice as a staple and are prone to vitamin-A deficiency, so the benefit is dietary. Tailor-made plants address an industrial and resource need: crops engineered to supply starches, fuels and pharmaceuticals act as renewable factories for raw materials, so the benefit reaches beyond food into industry. Together they show that GM crops can serve both the dinner plate and the factory floor.
Q29. Using the Basmati case, explain what biopiracy is, why developing nations are vulnerable to it, and what safeguards India put in place.
Answer: Biopiracy is the use of bio-resources by multinational companies and others without proper authorisation from the countries and people concerned and without compensatory payment. Developing nations are vulnerable because they are rich in biodiversity and traditional knowledge while industrialised nations are financially rich but biodiversity-poor, creating pressure to appropriate that knowledge. The Basmati case is the textbook example: in 1997 an American company patented Basmati rice, a 'new' variety actually derived from Indian farmers' varieties crossed with semi-dwarf ones, with similar attempts on turmeric and neem. Against biopiracy, India responded by clearing the second amendment of the Indian Patents Bill to protect its bio-resources; separately, the GEAC regulates the validity of GM research and the safety of releasing GM organisms.
Q30. Why is regulation of genetic modification treated as essential rather than optional, and what does GEAC weigh before approving GM work?
Answer: Regulation is essential for two reasons. Ethically, standards are needed to judge whether an activity helps or harms living organisms. Biologically, genetic modification can have unpredictable results once an organism is released into an ecosystem — effects that were never intended and cannot easily be reversed. To provide oversight, India set up the GEAC (Genetic Engineering Approval Committee), which weighs two things before green-lighting anything: the validity of the GM research and the safety of introducing GM organisms for public services such as food and medicine. GEAC thus acts as the gatekeeper between the laboratory and the public.
End of Section 12
You have now worked through 30 examples spanning tissue culture and totipotency, virus-free plants and somatic hybridisation, GM crops and golden rice, the Bt toxin and cry genes, RNA interference against the tobacco nematode, recombinant insulin, gene therapy for ADA deficiency, molecular diagnosis by PCR and ELISA, transgenic animals and Rosie, and the ethics of GM work and biopiracy. For every applications question, remember the three-part habit — technique or organism, molecular mechanism, and practical benefit or example — and you will rarely leave marks on the table.