NCERT Solutions for Class 12 Biology Chapter 10: Biotechnology and Its Applications

The meristem — specifically the apical meristem (shoot/root tip) and axillary meristem — is the part of the plant best suited for producing virus-free plants.

1. Why the meristem works. Even when the rest of a plant is infected with a virus, the meristem itself remains free of virus. This happens because meristematic cells divide extremely rapidly, growing faster than the virus can spread/replicate and move through the plant’s plasmodesmata into the newly forming tissue — so the actively growing meristematic tip effectively ‘outruns’ the infection.
2. The technique. Scientists excise this virus-free meristem and grow it in vitro, under sterile conditions on an appropriate nutrient medium, to regenerate a complete, healthy, virus-free plant.
3. Demonstrated examples. This method has been successfully used to culture meristems of banana, sugarcane and potato, recovering healthy plants even from diseased stock.

Conclusion: the apical and axillary meristem is virus-free even in an infected plant because its rapid cell division outpaces viral spread, so culturing just this tissue in vitro — as has been done for banana, sugarcane and potato — yields a completely healthy, virus-free plant.

The major advantage of micropropagation (producing thousands of plants through tissue culture) is that it allows the propagation of a very large number of genetically identical plants in a very short duration, starting from just a tiny explant of a single desirable parent plant.

1. Speed and scale. Thousands of plants can be generated far faster than through conventional seed-based propagation or breeding, which take much longer and depend on the plant’s natural reproductive cycle.
2. Genetic uniformity. Every plant produced is a somaclone — genetically identical to the original plant — guaranteeing that all the desirable characteristics of the parent (yield, disease resistance, fruit quality, etc.) are faithfully reproduced in every offspring, unlike seed propagation which can introduce genetic variation.
3. Commercial impact. This has enabled commercial-scale production of important food plants such as tomato, banana and apple.

Conclusion: micropropagation’s major advantage is that it rapidly generates a large number of genetically identical, desirable plants (somaclones) from a single explant, far faster and more reliably than conventional propagation methods.

An explant (any part of a plant taken out and grown in a test tube) can only regenerate into a whole plant — a capacity called totipotency — if it is supplied with a carefully balanced nutrient medium containing the following components:

Conclusion: a tissue-culture medium for in vitro propagation must supply a carbon source (sucrose), inorganic salts, vitamins, amino acids, and growth regulators (auxins and cytokinins), together providing everything the totipotent explant needs to regenerate into a complete plant.

Correct option: (c) toxin is inactive

As explained in this chapter, the Bt toxin protein exists as an inactive protoxin inside the bacterium Bacillus thuringiensis. It only becomes converted into its active, insecticidal form after an insect ingests it — the alkaline pH of the insect’s gut solubilises the crystal and activates the toxin, which then binds to midgut epithelial cells, creates pores, and causes cell swelling, lysis and death of the insect. Since the toxin inside the bacterium itself is never activated (no insect gut environment is present there), it cannot harm the bacterium that produced it.

Conclusion: the correct answer is (c) — the Bt toxin exists only as an inactive protoxin inside the bacterium and is converted to its active, cell-destroying form solely by the alkaline environment of an insect’s gut, which is why it cannot harm Bacillus thuringiensis itself.

Transgenic bacteria are bacteria whose genome has been artificially altered, using recombinant DNA technology, to carry and express an extra, foreign gene that does not naturally belong to that bacterial species — the bacterium is thereby made to manufacture a product (usually a protein) that it would not otherwise produce.

Example: genetically engineered human insulin in E. coli.

1. Human insulin consists of two short polypeptide chains, chain A and chain B, linked by disulphide bridges.
2. In 1983, the company Eli Lilly prepared two separate DNA sequences corresponding to the human insulin A chain and B chain.
3. These two DNA sequences were introduced into plasmids of Escherichia coli, making the bacteria transgenic — they now carried human genes foreign to their own genome.
4. The transgenic E. coli produced the A and B insulin chains separately; these were then extracted and chemically combined by forming disulfide bonds to assemble mature, fully functional human insulin.

In the human body itself, insulin is first synthesised as a single-chain pro-hormone (pro-insulin), containing an extra stretch called the C peptide between the A and B chain regions; this C peptide is enzymatically excised during maturation, leaving the two chains held together only by disulfide bridges — the same final structure that the transgenic-bacteria route had to reconstruct chemically from separately produced chains.

Conclusion: transgenic bacteria are bacteria engineered to carry and express a foreign gene, and the production of human insulin in transgenic E. coli — where the human insulin A and B chain genes were introduced via plasmids, expressed separately, and chemically joined — is the chapter’s own landmark example of this technology in practice.

Genetically modified (GM) crops are plants whose genes have been deliberately altered using biotechnology, most often to improve yield, resistance or nutritional quality. Like any powerful technology, GM crops bring substantial benefits alongside genuine, actively-debated concerns.

Advantages (directly stated in this chapter):

1. Greater tolerance to abiotic stress — cold, drought, salt and heat — letting crops survive and yield even under unfavourable environmental conditions.
2. Reduced reliance on chemical pesticides, through built-in pest resistance such as Bt cotton, lowering both cost and environmental/health harm from spraying toxic chemicals.
3. Reduced post-harvest losses, meaning more of what is grown actually reaches consumers.
4. Increased efficiency of mineral usage by the plant, which prevents the early exhaustion of soil fertility.
5. Enhanced nutritional value of food — e.g., golden rice, engineered to be enriched in Vitamin A, directly targeting micronutrient deficiency in populations that depend on rice as a staple.
6. GM technology also allows tailor-made plants that supply industries with alternative resources — starches, fuels and even pharmaceuticals.

Disadvantages/concerns (from the chapter’s own Ethical Issues section):

1. Unpredictable ecological effects. Genetic modification can have unpredictable results when such organisms are introduced into the ecosystem — effects on non-target species, gene flow to wild relatives, or impacts on biodiversity cannot always be anticipated in advance.
2. Need for strict regulation. Because of these risks, dedicated regulatory bodies such as India’s GEAC (Genetic Engineering Approval Committee) are required to evaluate every GM crop’s research validity and safety before public release — itself evidence of the real risk involved.
3. Patent and biopiracy disputes. GM and related biotechnology has led to companies patenting products/processes based on bio-resources and traditional knowledge long used by farmers and indigenous communities (e.g., the 1997 Basmati rice patent case), raising serious questions of fairness and ownership.
4. Cost and access. GM seeds and associated technology can be expensive, potentially increasing farmers’ dependence on seed-supplying companies rather than their own saved seed.

Conclusion: GM crops offer major agronomic and nutritional advantages — stress tolerance, reduced pesticide dependence, lower losses, better nutrition — but these come with real ecological uncertainty, the need for strict regulatory approval, and unresolved ethical/ownership disputes, which is why GM crop release is tightly regulated rather than left unchecked.

Cry proteins are the insecticidal crystal proteins (toxins) produced by the bacterium Bacillus thuringiensis (Bt) during a specific phase of its growth. They are coded by a family of genes collectively called cry genes (named for ‘crystal’).

1. Organism that produces them. Bacillus thuringiensis, a soil bacterium, produces these proteins as crystals that act as a natural insecticide against specific groups of insects — lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).
2. Specificity. Different cry genes control different pests — the proteins encoded by cryIAc and cryIIAb control cotton bollworms, while cryIAb controls the corn borer; this is why the choice of gene depends on both the crop and the targeted pest.
3. How man has exploited this protein. Scientists isolated the specific cry toxin genes from Bacillus thuringiensis and, using recombinant DNA technology, cloned and incorporated them directly into crop plants such as cotton, corn, rice, tomato, potato and soyabean. The plant itself then produces the Bt toxin, giving it built-in, continuous resistance to its target insect pests — effectively turning the crop into its own bio-pesticide and removing the need for repeated chemical insecticide spraying.

Conclusion: Cry proteins are the crystalline insecticidal toxins of Bacillus thuringiensis, and humans have exploited them by cloning the specific cry genes (such as cryIAc for bollworm or cryIAb for corn borer) directly into crop plants like Bt cotton, turning the crop itself into a built-in, chemical-free bio-pesticide.

Gene therapy is a collection of methods that allows correction of a gene defect that has been diagnosed in a child or embryo. Genes are inserted into a person’s cells and tissues to treat a disease; correcting the genetic defect involves delivering a normal, functional gene into the individual (or embryo) to take over the function of, and compensate for, the non-functional gene.

Illustration: Adenosine Deaminase (ADA) deficiency.

1. The disorder. ADA deficiency is caused by deletion of the gene for the enzyme adenosine deaminase, which is crucial for the immune system to function properly.
2. Conventional (non-curative) treatments. In some children, ADA deficiency can be managed by bone marrow transplantation; in others, by enzyme replacement therapy, in which functional ADA enzyme is injected into the patient. The problem with both approaches is that neither is completely curative.
3. The gene therapy procedure (1990, the first clinical gene therapy, given to a 4-year-old girl): lymphocytes are drawn from the patient’s blood and grown in culture outside the body; a functional ADA cDNA is introduced into these lymphocytes using a retroviral vector; the genetically engineered lymphocytes are then returned (infused back) into the patient.
4. Limitation of this approach. Because these treated lymphocytes are not immortal (they eventually die off), the patient requires periodic infusions of fresh genetically engineered lymphocytes to maintain the therapeutic effect.
5. Path to a permanent cure. If the correct ADA gene is instead introduced into cells (isolated from marrow cells producing ADA) at early embryonic stages, this could provide a truly permanent cure, since the corrected gene would then be present in all the cells descending from that early stage.

Conclusion: gene therapy treats a hereditary disease by delivering a normal gene to compensate for a defective one, and in ADA deficiency this was first achieved by introducing a functional ADA gene into a patient’s own cultured lymphocytes via a retroviral vector — a workable but non-permanent fix, with a true permanent cure requiring correction of the gene at the embryonic stage instead.

Cloning and expressing a human gene — here, the gene for human growth hormone (hGH) — in E. coli follows exactly the sequence of tools and processes built up across this chapter and the previous one: isolate the gene, cut and ligate it into a vector, transform a competent host, select the recombinants, and finally culture and process the product.

1. Isolation of the gene. The DNA sequence coding for human growth hormone is identified and isolated from human genetic material.
2. Cutting with restriction enzymes. Both the isolated hGH gene and a chosen cloning vector (plasmid) are cut using the same restriction enzyme, generating matching sticky ends on each.
3. Ligation to form recombinant DNA. The cut hGH gene and the cut vector are joined end-to-end using DNA ligase, producing a recombinant plasmid carrying the hGH gene, an origin of replication and a selectable marker.
4. Making the host competent and transformation. E. coli cells are treated with a divalent cation (e.g., CaCl₂) and given a brief heat shock at 42°C after incubation on ice with the recombinant plasmid, forcing uptake of the DNA.
5. Selection of recombinants. Transformed cells are plated on a medium containing the antibiotic corresponding to the vector’s resistance gene (selectable marker); only transformants carrying the plasmid survive.
6. Large-scale culture. Selected recombinant E. coli colonies are grown at large scale in a bioreactor under optimum temperature, pH, oxygen and nutrient conditions.
7. Expression and downstream processing. Once the hGH gene is expressed, the recombinant growth hormone protein is extracted and subjected to downstream processing — separation, purification, formulation and quality testing — before it is ready as a therapeutic product.

Conclusion: cloning and expressing the human growth hormone gene in E. coli follows the same universal recombinant DNA pipeline — isolate the gene, cut and ligate it into a vector, transform a competent host, select recombinants, culture at scale, and finally purify the expressed product through downstream processing.

Seed oils are chemically triglycerides — esters formed from glycerol and long hydrocarbon-chain fatty acids — synthesised inside the developing seed by a dedicated set of lipid-biosynthesis enzymes. Reducing the oil content of a seed, therefore, means reducing the activity of the genes that encode these specific oil-synthesising enzymes, which is exactly the kind of targeted gene-silencing problem that recombinant DNA technology, specifically RNA interference (RNAi), is designed to solve.

1. Identify the target genes. First, identify the specific genes in the seed that encode key enzymes of the oil/triglyceride biosynthesis pathway (e.g., enzymes that assemble fatty acid chains and link them to glycerol).
2. Apply the RNAi strategy used elsewhere in this very chapter. Exactly as was done to protect tobacco roots from the nematode Meloidegyne incognitia, a DNA construct can be introduced into the plant (using an Agrobacterium vector) that is designed to produce both sense and anti-sense RNA corresponding to the oil-biosynthesis gene(s), specifically in the seed tissue.
3. Silencing reduces oil synthesis. The sense and anti-sense RNA strands, being complementary, pair up to form double-stranded RNA (dsRNA), which triggers RNA interference — silencing the target mRNA and preventing its translation. With the oil-biosynthesis enzyme no longer being produced at normal levels, the seed accumulates substantially less oil.
4. Tissue-specific control. By using a seed-specific promoter to drive the sense/anti-sense RNA construct, the gene silencing can be restricted to the seed’s oil-storing tissue, leaving the rest of the plant’s normal lipid metabolism (e.g., in cell membranes) unaffected.

Conclusion: oil content in a seed can be reduced by using recombinant DNA technology to introduce a sense-and-anti-sense RNA construct against the seed’s own oil-biosynthesis genes, triggering RNA interference that silences those genes — the same dsRNA-mediated gene-silencing principle this chapter demonstrates for nematode-resistant tobacco, simply redirected at a plant’s own lipid-synthesis pathway instead of a parasite’s gene.

Golden rice is a genetically modified variety of rice, engineered so that its edible grain (endosperm) — which normally contains no beta-carotene at all — biosynthesises and accumulates beta-carotene, the plant pigment that is a direct precursor the human body converts into Vitamin A. The accumulated beta-carotene gives the grain its distinctive golden-yellow colour, which is how the rice gets its name.

1. Purpose. Golden rice was developed specifically to combat Vitamin A deficiency (VAD), a major public health problem in parts of the developing world where rice is a dietary staple but provides essentially no Vitamin A on its own — VAD is a leading cause of preventable childhood blindness and contributes significantly to child mortality in affected regions.
2. How it was engineered. Since ordinary rice endosperm lacks the complete enzymatic pathway to make beta-carotene, scientists introduced genes encoding the missing enzymes of the beta-carotene biosynthetic pathway (originally sourced from daffodil and a soil bacterium, in the pioneering version of golden rice) into the rice genome, specifically engineered to be active in the grain’s endosperm.
3. Significance. As this chapter itself notes, golden rice is a prime example of how genetic modification can enhance the nutritional value of food — turning a staple crop that people already eat daily into a vehicle for delivering an essential micronutrient, without requiring any change in diet or added supplementation programmes.

Conclusion: golden rice is a genetically engineered rice variety that accumulates beta-carotene (a Vitamin A precursor) in its edible grain, created specifically to fight Vitamin A deficiency in populations that rely on rice as a dietary staple — a leading real-world example of using GM technology to improve the nutritional quality of food.

Yes — human blood contains both proteases and nucleases, playing essential physiological roles.

This is precisely why a protein drug such as insulin cannot simply be swallowed as a tablet — if taken orally, it would be broken down by the body’s own digestive proteases (in the stomach and intestine) before it could ever reach the bloodstream intact, exactly as any other dietary protein is digested.

Conclusion: yes, blood contains proteases (such as thrombin and plasmin, central to clotting and its reversal) and nucleases (serum DNase/RNase activity, which clear circulating nucleic acids) — a fact that also explains why protein-based drugs like insulin must be injected rather than taken by mouth.

The major problem in making any protein pharmaceutical orally active is that proteins, when swallowed, pass through the highly acidic environment of the stomach and are attacked by digestive proteases in the stomach and intestine — exactly like any dietary protein — and are broken down into amino acids/peptide fragments before they can be absorbed intact into the bloodstream in their functional form. This is precisely why insulin, itself a protein, cannot currently be taken as a tablet and must instead be injected.

Approaches researchers use to try to overcome this problem:

1. Protective encapsulation. Encasing the protein in a protective carrier — such as liposomes, nanoparticles, or an enteric (acid-resistant) coating — that shields it from stomach acid and digestive enzymes until it reaches a more favourable site for absorption further down the gut.
2. Chemical modification of the protein. Techniques such as PEGylation (attaching polyethylene glycol chains) can make the protein more resistant to protease degradation and increase its stability in circulation.
3. Permeation enhancers. Co-formulating the drug with agents that temporarily increase the permeability of the intestinal lining, helping more of the intact protein cross into the bloodstream.
4. Co-administered protease inhibitors. Including substances that temporarily inhibit the digestive proteases in the local area of absorption, giving the protein drug a better chance of surviving intact.
5. Engineering a protease-resistant version of the protein itself, modifying its structure at vulnerable cleavage sites while preserving its biological activity.

Conclusion: the major obstacle to an orally active protein pharmaceutical is digestion of the protein by the body’s own proteases before it can be absorbed intact, and researchers try to overcome this through protective encapsulation, chemical modification, permeation enhancers, protease inhibitors, or re-engineering the protein itself to resist digestion.