Previous year questions: Biotechnology and its Applications

Board pattern for this chapter

The chapter supplies short definition questions, one-line identifications, and longer answers on Bt technology, insulin and gene therapy. All ten questions below are rewritten from actual CBSE board papers between 2022 and 2024. The marks in each heading tell you how long the answer should be, and the year tells you which paper to open for the original.

Q1 (CBSE Board 2022, 3 marks)

Bt toxin genes protect crops against specific pests. (a) Which cry gene controls the corn borer? (b) Explain how the Bt toxin made by the bacterium kills an insect.

Answer: (a) cryIAb controls the corn borer, and each cry gene is chosen for the pest it targets. (b) The bacterium stores the toxin as an inactive protoxin inside protein crystals. When an insect eats the crystal, the alkaline pH of its gut dissolves it and converts the protoxin into the active toxin. Once active, the toxin attaches to midgut epithelial cells, punches pores in them, and the cells swell and burst, killing the insect. The bacterium itself is unaffected because the toxin stays inactive inside it.

Q2 (CBSE Board 2022, 3 marks)

Bacillus thuringiensis plays an important role in integrated pest management. Explain how, and name any two crops protected efficiently from pests.

Answer: Bacillus thuringiensis makes insecticidal crystal proteins that are specific to certain insect groups, such as lepidopterans, coleopterans and dipterans. The bacterium is used as a biological insecticide, and its cry genes have been transferred into crops, so the plant makes its own toxin and needs fewer chemical sprays. This fits integrated pest management, which combines biological control with other methods instead of depending only on chemicals. Bt cotton and Bt corn are two protected crops. The same approach explains why Bt crops are counted as a biocontrol method and not as a chemical spray: the protection is built into the plant rather than added from outside.

Q3 (CBSE Board 2022, 3 marks)

With the help of a storyboard or a flowchart only, explain all the stages by which human insulin is produced using recombinant DNA technology.

Answer: Human insulin has two polypeptide chains, A and B, joined by disulphide bonds. In the body it is first made as a pro-hormone with an extra C peptide, which is removed during maturation. For recombinant production, two DNA sequences corresponding to the A and B chains are prepared and inserted into plasmids of Escherichia coli. The chains are produced separately, extracted from the bacteria, and then joined by creating disulphide bonds to form mature human insulin.

Q4 (CBSE Board 2022, 2 marks)

This is 57/5/1 Q11(a), a two-mark part. How is gene therapy used in the treatment of adenosine deaminase deficiency?

Answer: ADA deficiency is caused by deletion of the gene for adenosine deaminase, an enzyme needed for the immune system to work. For gene therapy, lymphocytes are collected from the patient and grown outside the body, and a working ADA cDNA goes into them through a retroviral vector, and the engineered lymphocytes are returned to the patient. Since lymphocytes are not immortal, the patient needs periodic infusions of these cells. If the functional gene could be introduced at an early embryonic stage, the cure could be permanent.

Q5 (CBSE Board 2023, 5 marks)

Answer the following about Bt cotton. (i) Why do farmers prefer Bt cotton over unmodified cotton? (ii) Name any two insects killed by Bt toxin. (iii) Explain why Bt toxin kills the insect but not the bacterium that makes it.

Answer: (i) Bt cotton carries a Bt toxin gene from Bacillus thuringiensis, so the plant itself is protected against the cotton bollworm. Farmers need fewer insecticide sprays, which saves cost and reduces chemical load on the field. (ii) The cotton bollworm and the tobacco budworm are killed by Bt toxin. (iii) Inside the bacterium the toxin is stored as an inactive protoxin in crystals, so it cannot harm the bacterium. After an insect eats the toxin, the alkaline pH of its gut dissolves the crystal and activates the toxin, which then makes pores in midgut cells and kills the insect.

Q6 (CBSE Board 2024, 1 mark)

The specific Bt toxin genes that protect cotton plants against cotton bollworms are

(A) Cry-I Ac and Cry-II Ab (B) Cry-I Ab and Cry-I Bc (C) Cry-II Ac and Cry-I Ac (D) Cry-II Ab and Cry-I Ab

Answer: Option (A), Cry-I Ac and Cry-II Ab. The proteins from cryIAc and cryIIAb control the cotton bollworms, while cryIAb controls the corn borer.

Q7 (CBSE Board 2024, 3 marks)

(a) What are transgenic animals? (b) Name the transgenic animal that is largest in number among all existing transgenic animals. (c) State any three reasons for which transgenic animals are produced.

Answer: (a) Transgenic animals are animals whose DNA has been manipulated so that they carry and express an extra foreign gene. (b) Mice form more than 95 per cent of all existing transgenic animals. (c) Three reasons: they act as disease models, for cancer and cystic fibrosis among others; they yield useful biological products, as Rosie's milk showed; and they serve in safety tests for vaccines and toxic substances.

Q8 (CBSE Board 2024, 1 mark)

The improved trait found in the genetically modified crop Golden rice is

(A) high lysine content (B) insect resistant (C) high protein (D) high vitamin-A

Answer: Option (D), high vitamin-A. Golden rice is the textbook's example of a GM crop with enhanced nutritional value.

Q9 (CBSE Board 2024, 1 mark)

Which transgenic animal is used in polio vaccine safety testing?

(A) sheep (B) goat (C) pig (D) mice

Answer: Option (D), mice. Transgenic mice already test polio vaccine batches; if their results hold up, they can replace monkeys in batch checks.

Q10 (CBSE Board 2024, 1 mark)

Assertion (A): In molecular diagnosis, a single stranded DNA or RNA carrying a radioactive tag is called a probe. Reason (R): A probe finds the sequence complementary to it and pairs with that sequence.

Answer: Both A and R are true, and R correctly explains A. A probe is a tagged single stranded nucleic acid that finds its complementary sequence in a clone of cells. Autoradiography then shows where the probe has bound, and a mutated clone fails to show a spot because its sequence is not complementary to the probe.

What the board rewards

This chapter rewards named genes, named organisms and ordered mechanisms. Keep the Bt mechanism in four steps, the insulin story in four steps and the ADA gene therapy in five. For the one-mark questions, the exact gene or animal matters more than a sentence of explanation. A useful revision drill is to say the answer out loud before writing it: if the gene name or the animal name does not come in the first sentence, the mark is already at risk. For the five-mark question on Bt cotton, answer all three parts even if one part seems short, because each carries its own mark.

Three traps in this chapter

The first trap is mixing up the two kinds of ADA treatment. Enzyme replacement therapy injects working enzyme; gene therapy puts a working gene into the patient's cells. Only the second is gene therapy, and only the second needs a vector. The second trap is writing that Bt toxin is a chemical sprayed on crops. In Bt crops the gene is inside the plant, so the plant itself makes the protoxin. The third trap is treating the GEAC as a patent authority. It clears GM research and the release of GM organisms; patents are a separate legal process. When a question combines two ideas, for example RNAi plus transgenic plants, answer both halves in separate sentences so the examiner can award the two marks separately.

A five minute revision order

Read the three topic pages in reverse: start with biopiracy, move to gene therapy, and finish with Bt cotton. The topics get harder in that order and the easy definitions at the end of a revision session stick better. Then say the three mechanisms aloud: Bt activation, RNAi silencing and ADA gene therapy. If one of the three stalls, open that topic page rather than rereading the whole chapter.