Q.‘‘Cotton bollworms enjoy feeding on cotton plants, but get killed when feed on Bt cotton plant.’’ Justify the statement.
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🔒 Start your 14-day free trial to unlock the full solution →Part (a)Concept understanding — Genetically Modified Organisms
Imagine you have a recipe for a simple sponge cake. Now, suppose you want that cake to also have chocolate chips inside it. You wouldn't throw away the original recipe and start from scratch. Instead, you would take the basic cake batter and deliberately add chocolate chips to it. You have modified the original recipe to give it a new, useful property.
A Genetically Modified Organism (GMO) works on the same principle, but instead of adding chocolate chips to batter, scientists add a specific gene (a tiny instruction manual inside a living cell) from one organism into the DNA of another organism. The result is a living thing — a plant, animal, or microbe — whose genetic material has been artificially altered in a way that does not occur naturally through mating or natural recombination.
The key word here is deliberate. GMOs are not the same as the natural evolution or selective breeding that farmers have done for thousands of years (like breeding wolves into dogs). Selective breeding mixes thousands of genes at once, like shuffling two entire decks of cards. Genetic modification is like taking a single, specific card from one deck and inserting it into a specific spot in another deck.
How does it actually work? (The core idea)
Every living thing — from a bacterium to a mango tree to a human — carries its hereditary information in a molecule called DNA. A gene is a specific segment of that DNA that contains the instructions for making one particular protein. That protein then gives the organism a particular trait, like the colour of a flower or the ability to resist a pest.
In genetic modification, scientists:
- Identify a useful gene from one organism (say, a gene from a soil bacterium that makes a protein toxic to certain insects).
- Isolate that gene and copy it.
- Insert that gene into the DNA of a different organism (say, a cotton plant).
- The cotton plant now reads that new gene and starts producing the insect-killing protein. The cotton plant has been genetically modified to be pest-resistant.
Why does this matter? (The real-world significance)
GMOs are not just a lab curiosity. They are a major part of modern agriculture and medicine. The NCERT textbook highlights two main areas where this technology has had a huge impact:
1. Agriculture: Making crops more useful
The most common GMOs you will encounter are crop plants. The goal is usually to give the plant a new, valuable trait without having to breed it for many generations.
- Pest resistance (Bt crops): A gene from the bacterium Bacillus thuringiensis (Bt) is inserted into crops like cotton and corn. This gene produces a protein that kills specific insect pests (like the cotton bollworm). The plant protects itself, so farmers need to spray fewer chemical pesticides.
- Herbicide tolerance: Some crops are modified to be resistant to a specific weed-killer (herbicide). This allows farmers to spray the herbicide to kill weeds without harming the crop itself.
- Increased nutritional value: A famous example is Golden Rice, which is genetically modified to produce beta-carotene (which the body converts to Vitamin A). This was developed to address Vitamin A deficiency in regions where rice is a staple food.
The NCERT textbook specifically mentions Bt cotton as a major success story in India. It has been widely adopted by farmers because it reduces the need for pesticides and can lead to higher yields. However, it also raises important questions about cost, seed patents, and long-term effects on soil and biodiversity — issues that are debated in economics and environmental studies.
2. Medicine: Producing life-saving drugs
This is where GMOs have had an arguably even more profound impact. Instead of modifying whole plants, scientists often modify microorganisms like bacteria or yeast to act as tiny factories.
- Human Insulin (Humulin): Before GMOs, people with diabetes used insulin from cows or pigs, which could cause allergic reactions. Scientists inserted the human gene for insulin into E. coli bacteria. The bacteria then multiplied and produced large quantities of pure human insulin. This was the first-ever commercial GMO product approved for human use.
- Vaccines and other proteins: Many modern vaccines (like the Hepatitis B vaccine) and other therapeutic proteins are now produced using genetically modified yeast or animal cells. This is safer, cheaper, and more scalable than extracting them from human or animal tissues.
A balanced perspective (What you should know) …
Part (b)Concept understanding — Recombinant DNA Technology
Imagine you have a cookbook with recipes from all over the world. Normally, you can only cook what's in one book at a time. But what if you could cut out the best recipe from one book and paste it into another, so your new book has a dish that no single cuisine ever had before? That is the basic idea behind Recombinant DNA Technology.
At its simplest, this technology is a way to take a piece of DNA (the genetic instruction manual) from one organism and join it with the DNA of a completely different organism. The result is a new, "recombinant" DNA molecule — a hybrid that never existed in nature. Think of it as genetic tailoring: you cut a gene from a human, a bacterium, or a plant, and stitch it into the DNA of another organism, often a bacterium or yeast. That host organism then reads the new instructions and starts producing the protein the inserted gene codes for.
Why does this matter? Because it lets us manufacture things that living organisms naturally make, but in a controlled, large-scale way. For example, the human insulin gene can be inserted into E. coli bacteria. These bacteria then become tiny factories, churning out human insulin that can be purified and given to diabetic patients. Before this technology, insulin had to be extracted from the pancreases of cows and pigs — a slow, expensive, and sometimes allergenic process.
The NCERT textbook (Class 12 Biology, Chapter 11) defines it precisely: Recombinant DNA Technology is the technique of joining DNA from two different species and inserting it into a host organism to produce a new genetic combination. The textbook highlights three key tools that make this possible:
- Restriction Enzymes – These are the "molecular scissors" that cut DNA at specific, predictable points. They allow scientists to cut out a desired gene cleanly.
- Vectors – These are the "delivery vehicles," usually plasmids (small circular DNA in bacteria) or viruses, that carry the foreign DNA into the host cell.
- Host Organisms – The living factory (like bacteria, yeast, or plant cells) that will replicate the recombinant DNA and produce the desired protein.
The core principle is genetic recombination — creating a DNA molecule that contains sequences from two or more different sources. This is not the same as natural reproduction or mutation; it is a deliberate, laboratory-made hybrid.
The process itself follows a clear sequence:
- Isolation of the desired gene (say, the human insulin gene) from the donor organism's DNA.
- Cutting both the gene and the vector DNA with the same restriction enzyme, creating matching "sticky ends."
- Ligation — using an enzyme called DNA ligase to permanently join the gene and the vector, forming the recombinant DNA.
- Transformation — inserting this recombinant DNA into a host cell (like a bacterium).
- Selection — identifying and growing only those host cells that successfully took up the recombinant DNA.
- Expression — getting the host cells to produce the desired protein in large quantities.
A common confusion is thinking this technology creates "new life." It does not. It creates a new genetic combination inside an existing living cell. The host organism remains the same species, but it now carries an extra instruction — like a factory that gets a new blueprint for a product it never made before. …
Part (a)
The statement is justified. Bt cotton is a transgenic plant carrying a cry gene from the bacterium Bacillus thuringiensis, so the plant itself makes the Bt protein (a protoxin).
- Ordinary cotton has no such defence, so bollworms feed and thrive on it.
- When a bollworm feeds on Bt cotton, it ingests the crystal protein. In the insect's alkaline gut the inactive protoxin is converted into the active toxin, which binds to the midgut epithelium and creates pores, causing the gut to swell and lyse. The larva stops feeding and dies. …
Part (a): Bt cotton carries a Bacillus thuringiensis cry gene, so it makes a protoxin that turns into an active gut toxin in the bollworm and kills it.
Part (b): ADA deficiency is caused by a defective ADA gene; gene therapy inserts a functional gene into the patient's lymphocytes (repeated periodically), and a permanent cure needs the gene placed in dividing bone-marrow/embryonic cells.
Part (a)
The cotton bollworm is a serious pest that feeds on the leaves and bolls of cotton. Ordinary cotton has no in-built protection, so the bollworm feeds and multiplies on it freely.
Bt cotton is a genetically modified (transgenic) plant: scientists have inserted into it a cry gene obtained from the soil bacterium Bacillus thuringiensis. This gene codes for an insecticidal crystal (Cry) protein, which the plant now produces in its own tissues. Importantly, the protein is made as an inactive protoxin. …
Showing the 12 most recent of 64 on this concept.
- CBSE 2026Set 57/1/11 markMCQQ.Which of the following statements about plasmids is incorrect ? (A) Plasmids have the ability to replicate within the bacterial cell. (B) Their replication is controlled by chromosomal DNA. (C) They are autonomously replicating circular extra-chromosomal DNA. (D) They often carry antibiotic resistant genes.
›Reveal solutionSolution
The incorrect statement about plasmids is that their replication is controlled by chromosomal DNA; plasmids replicate autonomously.
Plasmids are fascinating and crucial components in the world of microbiology and biotechnology. They are essentially small, circular, extra-chromosomal DNA molecules found predominantly in bacteria, but also in some eukaryotes like yeast. Think of them as accessory genetic units that carry non-essential but often beneficial genes for the host cell.
Let's break down the given statements to understand which one is incorrect:
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Statement (A): Plasmids have the ability to replicate within the bacterial cell.
This statement is correct. A defining feature of plasmids is their ability to self-replicate. They possess their own origin of replication (ori) sequence, which allows them to initiate DNA synthesis independently of the main bacterial chromosome. This autonomous replication is what makes them incredibly useful as vectors in genetic engineering, as they can multiply along with the host cell, carrying the inserted foreign DNA.
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Statement (B): Their replication is controlled by chromosomal DNA.
This statement is incorrect. As mentioned above, plasmids replicate autonomously. This means their replication is independent of the bacterial cell's main chromosomal DNA replication. While the host cell's machinery (enzymes, nucleotides) is used for plasmid replication, the initiation and control of plasmid replication are governed by sequences within the plasmid itself, not by the bacterial chromosome. This independence is a key distinction between plasmids and the main chromosome.
ImportantThe autonomous replication of plasmids, independent of the host cell's chromosomal DNA, is a fundamental characteristic that distinguishes them and makes them invaluable tools in molecular biology.
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Statement (C): They are autonomously replicating circular extra-chromosomal DNA.
This statement is correct. This is a precise definition of a plasmid.
- Autonomously replicating: They have their own origin of replication and can replicate independently.
- Circular: Most plasmids are found in a closed circular form. …
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- CBSE 2026Set 57/2/11 markMCQQ.Assertion (A) : DNA Ligase is used to join DNA fragments. Reason (R) : It catalyses the formation of glycosidic bonds between nucleotides. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation for Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not correct explanation for Assertion (A). (C) Assertion (A) is true, Reason (R) is false. (D) Assertion (A) is false, Reason (R) is true.
›Reveal solutionSolution
DNA Ligase joins DNA fragments by catalysing phosphodiester bonds, not glycosidic bonds. So Assertion is true, Reason is false — option (C).
The question tests a very specific piece of molecular biology: what bond does DNA Ligase actually form? Many students memorise "DNA Ligase joins fragments" but forget the exact chemistry. Let's break it down cleanly.
Why the Assertion is correct
DNA Ligase is the enzyme used in DNA replication, repair, and genetic engineering to seal nicks in the DNA backbone. It joins two DNA fragments — for example, an Okazaki fragment to the growing lagging strand, or an insert into a plasmid vector. This is a standard fact in biotechnology and molecular biology.
Why the Reason is wrong
The Reason claims DNA Ligase catalyses the formation of glycosidic bonds between nucleotides. That is a critical error.
- A glycosidic bond links a sugar (deoxyribose) to a nitrogenous base (A, T, G, C) — that bond is formed during nucleotide synthesis, not by DNA Ligase.
- DNA Ligase catalyses the formation of a phosphodiester bond between the 3'-hydroxyl group of one nucleotide and the 5'-phosphate group of the next nucleotide. This is the bond that holds the sugar-phosphate backbone together.
Watch outA common mistake is confusing "joining nucleotides" with "forming the bond between sugar and base." The bond between nucleotides in a DNA strand is always phosphodiester, never glycosidic.
Step-by-step reasoning
- Evaluate Assertion (A): "DNA Ligase is used to join DNA fragments." …
- CBSE 2026Set 57/3/11 markMCQQ.Golden rice is a promising transgenic crop. When released for cultivation, it will help in : (A) Producing petrol-like fuel (B) Reduction of Vitamin A deficiency in humans (C) Pest resistance (D) Herbicide tolerance
›Reveal solutionSolution
Golden rice is a genetically modified crop engineered to produce beta-carotene, which the human body converts into Vitamin A, making it a tool to combat Vitamin A deficiency.
Golden rice is one of the most well-known examples of a genetically modified organism (GMO) developed for humanitarian purposes. To understand what it does, we first need to step back and look at why it was created. Vitamin A deficiency is a serious public health problem in many developing countries, particularly in parts of Asia and Africa where rice is a dietary staple. Rice, however, contains no beta-carotene (the precursor to Vitamin A) in its polished grain. People who rely heavily on rice and lack access to diverse foods like carrots, leafy greens, or animal products often suffer from blindness, weakened immunity, and even death due to this deficiency.
Scientists addressed this by inserting two genes into the rice genome: one from a soil bacterium (Erwinia uredovora) and one from a daffodil plant. These genes enabled the rice plant to produce beta-carotene in the endosperm — the part of the grain we eat. The beta-carotene gives the rice a characteristic golden-yellow colour, hence the name "golden rice." When consumed, the human body converts this beta-carotene into Vitamin A.
NoteGolden rice is not intended to replace a balanced diet or Vitamin A supplements. It is designed as a supplementary intervention for populations where rice is the primary food and access to other sources of Vitamin A is limited. …
- CBSE 2026Set EG1 markQ.Write the name of any one transgenic animal.
›Reveal solutionSolution
A transgenic animal example: the cow Rosie (or a transgenic mouse).
A transgenic (genetically modified) animal is one that carries a foreign (manipulated) gene deliberately introduced into it. A well-known example is the transgenic cow Rosie, which produced human protein-enriched milk (containing human alpha-lactalbumin), making the milk more balanced for human babies.
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- CBSE 2026Set A1 markMCQQ.Which technique was used to prevent infection of tobacco plants from Meloidegyne incognitia tapeworm?(a) RNA interference(b) Cry protein(c) Somatic hybridisation(d) Pesticide
›Reveal solutionSolution
RNA interference protected tobacco from the nematode; the correct option is (a).
The root parasite Meloidogyne incognita (a nematode, not a tapeworm as the stem loosely states) infects tobacco plants and reduces yield. Protection was achieved using RNA interference (RNAi). Using Agrobacterium as a vector, nematode-specific genes were introduced into the host plant to produce both sense and antisense RNA. These form a double-stranded RNA …
- CBSE 2026Set A1 markMCQQ.Which human protein is found in milk of the first transgenic cow-Rosie?(a) Alpha-1 antitrypsin(b) Alpha lactalbumin(c) Albumin(d) p53
›Reveal solutionSolution
Rosie's milk contained human alpha-lactalbumin; the correct option is (b).
Rosie, the first transgenic cow (1997), produced human protein-enriched milk containing about 2.4 grams per litre of human alpha-lactalbumin. This human protein made the milk nutritionally more balanced and suitable for human babies than ordinary cow's milk. It …
- CBSE 2026Set ANNUAL1 markQ.Which nematode infected the roots of tobacco plant and causes a great reduction in the yield?
›Reveal solutionSolution
The nematode Meloidogyne incognita infects tobacco roots and reduces yield; RNA interference (RNAi) technology has been used to make tobacco plants resistant to it.
Meloidogyne incognita is a nematode that infects the roots of tobacco plants, causing considerable reduction in yield. Using recombinant DNA technology, RNA interference (RNAi) was used to introduce nematode-specific genes into tobacco cells via Agrobacterium ve …
- CBSE 2026Set ANNUAL1 markMCQQ.Given below are the steps carried out to construct a recombinant DNA.(i) Isolation of genetic material(ii) Insertion of recombinant DNA in the host cell /organism(iii) Obtaining the foreign gene product(iv) Amplification of gene of interest(v) Downstream processing. Which one of the following gives the correct sequences of these steps?(a)(i)(iii)(iv)(ii)(v)(b)(i)(iv)(ii)(iii)(v)(c)(ii)(i)(iii)(iv)(v)(d)(ii)(iv)(v)(iii) (i)
›Reveal solutionSolution
Constructing and using recombinant DNA follows a fixed logical sequence: first isolate and amplify the gene of interest, then insert the recombinant DNA into a host, let the host express the gene product, and finally process that product for use — i.e., (i) → (iv) → (ii) → (iii) → (v).
Recombinant DNA technology (genetic engineering) involves several sequential processes:
- (i) Isolation of genetic material (DNA) — the DNA must first be extracted in a pure form from the source cell, free of other macromolecules.
- (iv) Amplification of the gene of interest — using restriction enzymes to cut out the desired gene and, typically, PCR to amplify it, then ligating it into a suitable vector to form the recombinant DNA.
- (ii) Insertion of the recombinant DNA into the host cell/organism — the recombinant DNA (vector + gene of interest) is introduced into a competent host cell (transformation) and the host is then cultured/multiplied so the gene is expressed. …
- CBSE 2025Set ANNUAL1 markMCQQ.An important objective of biotechnology in the area of agriculture is -(a) to decrease seed number(b) to produce pest-resistant varieties of plants(c) to increase phosphorous, nitrogen production(d) to reduce the number of plants
›Reveal solutionSolution
Agricultural biotechnology mainly aims at developing pest-resistant crop varieties, such as Bt crops.
A key objective of biotechnology applied to agriculture is to reduce dependence on chemical pesticides by developing genetically modified, pest-resistant crop varieties — for example, Bt cotton and Bt brinjal, which carry cry genes from the soil bacterium Bacillus thuringiensis that make plant tissue toxic to specific insect larvae. This raises crop yield and lowers the …
- CBSE 2025Set KH1 markMCQQ.Bt cotton formed from:(a) Virus(b) Fungi(c) Bacteria(d) Insects
›Reveal solutionSolution
The Bt toxin gene (cry) comes from the bacterium Bacillus thuringiensis, so Bt cotton is formed using bacteria → option (c).
Concept. "Bt" stands for Bacillus thuringiensis, a soil bacterium that produces crystal (Cry) proteins toxic to certain insect larvae.
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- CBSE 2025Set ANNUAL1 markMCQQ.Golden rice is a genetically modified crop where the incorporated gene is meant for biosynthesis of(a) vitamin B(b) vitamin A(c) vitamin E(d) vitamin C
›Reveal solutionSolution
Golden rice is engineered to produce beta-carotene in its grain, which the human body converts into vitamin A.
Golden rice is a transgenic variety of rice engineered by introducing genes for the biosynthesis of beta-carotene (which gives the grain its golden-yellow colour), a compound the human body can readily convert into vitamin A. It was developed specifically to …
- CBSE 2025Set ANNUAL1 markMCQQ.Which one of the following is not required for rDNA technology ?(i) DNA polymerase(ii) DNA ligase(iii) Restriction endonuclease(iv) Reverse transcriptase
›Reveal solutionSolution
Basic recombinant DNA technology always needs a cutting enzyme (restriction endonuclease), a joining enzyme (DNA ligase) and DNA-copying capability (DNA polymerase, e.g. for PCR); reverse transcriptase is only needed in the special case of starting from an RNA/mRNA template, so it is the one "not required" in general.
The core enzyme toolkit of rDNA technology includes:
- Restriction endonucleases: "molecular scissors" that cut DNA at specific recognition sequences to isolate the gene of interest and to open up the vector for insertion — always required.
- DNA ligase: joins ("glues") the cut gene of interest into the vector DNA to form the recombinant DNA molecule — always required.
- DNA polymerase: needed for amplifying DNA (e.g. via PCR) and is also the enzyme the host cell itself uses to replicate the recombinant plasmid — required in essentially every rDNA procedure. …
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