Biotech Agriculture Bt Gm

8 MCQs9-step worked example
Source: NCERT BiomoleculesPYQ coverage: NEET 2020, 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

The trap that costs marks here: confusing which GM strategy gives which trait. Bt crops, RNAi crops, and herbicide-tolerant crops each use a different gene and a different mechanism — NEET questions test whether you can match them correctly.

Bt crops express Cry proteins (from Bacillus thuringiensis) inside plant tissues. When a target insect — cotton bollworm (Helicoverpa armigera) for Bt cotton, corn borer for Bt corn — ingests the plant tissue, the inactive protoxin (Cry protein) is solubilised in the alkaline insect gut, converted to active toxin, and creates pores in midgut epithelial cells. The insect dies. The plant is not sprayed with anything — it produces the toxin endogenously (NCERT Class 12 Biology Chapter 11, page 236).

Specific Cry genes and their targets:

  • Cry1Ac, Cry2Ab → cotton bollworms (lepidopterans)
  • Cry1Ab → corn borer (lepidopteran)

RNAi-based resistance uses a different mechanism entirely: RNA interference silences a specific nematode gene. The classic NCERT example is tobacco engineered to resist root-knot nematode (Meloidogyne incognita) by producing dsRNA complementary to a nematode mRNA. This is gene silencing, not a toxin.

Herbicide-tolerant GM crops carry genes like bar or EPSPS that allow the plant to survive broad-spectrum herbicides (e.g., glyphosate). The crop lives; the weeds die.

Watch-out: A common NEET distractor describes Bt cotton as "spraying" Cry protein externally. That confuses Bt spray (used in organic farming) with Bt transgenic crops (endogenous expression). The protein is made inside the plant cells — no spray involved.

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

Which of the following Cry genes codes for a protein toxic to cotton bollworm?

MCQ 2Easy RecallPractice

In Bt cotton, the Cry protein is:

MCQ 3Easy RecallPractice

RNAi-based resistance in transgenic tobacco protects against which pest?

MCQ 4Direct ApplicationPractice

A transgenic crop is engineered with the *EPSPS* gene. This crop would be expected to show resistance to:

MCQ 5Direct ApplicationPractice

The mechanism by which Bt toxin kills the target insect involves:

MCQ 6Direct ApplicationPractice

Which of the following correctly matches the GM strategy with its mechanism?

MCQ 7Concept TrapPractice

A student claims: "Bt cotton and Bt biopesticide spray work the same way — both put Bt toxin on the plant surface to kill insects on contact." What is wrong with this claim?

MCQ 8CalculationPractice

An agricultural scientist is developing a GM crop that must simultaneously resist lepidopteran pests AND tolerate glyphosate herbicide. Which combination of transgenes would be required?

Worked Example

  1. 1

    Given

    - The crop is transgenic cotton (Bt cotton). - It produces a protein lethal to cotton bollworm larvae upon ingestion. - The question asks for gene source, gene identity, kill mechanism, and distinction from Bt spray.

  2. 2

    Required

    Identify the organism, gene(s), mechanism of action, and the key difference between transgenic Bt expression and external Bt spray.

  3. 3

    Concept

    Bt cotton carries cry genes from *Bacillus thuringiensis* integrated into its genome. The expressed Cry protein is a protoxin that becomes active in the alkaline gut of susceptible insects.

  4. 4

    Relevant information

    - Source organism: *Bacillus thuringiensis* - Genes for cotton bollworm: Cry1Ac, Cry2Ab - Activation: alkaline gut pH solubilises protoxin → active toxin - Mode of killing: pore formation in midgut epithelial cells - Bt spray: external application on plant surface; Bt transgenic: endogenous production inside plant cells

  5. 5

    Identification/Reasoning

    (a) The gene comes from *Bacillus thuringiensis*, a soil bacterium. (b) The specific genes are **Cry1Ac** and **Cry2Ab** — both target lepidopteran pests that attack cotton. (c) The Cry protein is produced as an inactive protoxin inside plant cells. When a bollworm larva ingests plant tissue, the protoxin enters the larval gut (pH > 9.5), is solubilised, and proteolytic enzymes cleave it into the active Bt toxin. The active toxin binds to specific receptors on midgut epithelial cells, creating pores. This causes cell lysis, gut perforation, septicaemia, and death. (d) In Bt spray, the toxin is applied externally and sits on the plant surface — it degrades with UV and rain. In Bt cotton, the Cry protein is synthesised endogenously within every cell of the plant, providing continuous protection without reapplication and without surface residue.

  6. 6

    Answer assembly

    | Part | Answer | |------|--------| | (a) Source organism | *Bacillus thuringiensis* | | (b) Gene(s) | Cry1Ac, Cry2Ab | | (c) Kill mechanism | Protoxin → alkaline gut activation → midgut pore formation → cell lysis → insect death | | (d) Bt spray vs Bt crop | Spray = external, degrades; Bt crop = endogenous expression in plant cells, continuous |

  7. 7

    Final answer

    Bt cotton carries Cry1Ac and Cry2Ab genes from *Bacillus thuringiensis*. The plant produces Cry protoxin endogenously; upon ingestion by bollworm larvae, the alkaline gut activates the toxin, which creates pores in midgut epithelial cells, killing the larva. Unlike Bt spray (external, degradable), the transgenic protein is continuously produced inside plant tissues.

  8. 8

    Common trap

    Stating that Bt cotton "sprays" or "coats" the plant surface with Cry protein. This confuses Bt biopesticide spray (an organic farming input applied externally) with Bt transgenic expression (gene integrated into plant genome, protein made inside cells).

  9. 9

    Similar NEET-style question

    *"Golden rice is a transgenic crop enriched with β-carotene. Which of the following correctly identifies the gene strategy — Bt toxin, RNAi, or metabolic pathway engineering?"* (Answer: metabolic pathway engineering — introduction of phytoene synthase and carotene desaturase genes, not Bt or RNAi.) ---

Before solving, remember these

Key Fact

Biotech in agriculture

Bt cotton: Cry1Ac (bollworm), Cry2Ab. Bt corn: Cry1Ab. RNAi (RNA interference): nematode resistance in tobacco. Pest-resistant, herbicide-tolerant (Roundup-Ready) GM crops.

-- NCERT Class 12 Biology, Ch. 11, p. 236

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Bt vs RNAi vs herbicide-tolerant GM crop confusion

Category: Similar Terms

Bt: insect resistance (Cry toxin). RNAi: nematode resistance via gene silencing. Herbicide-tolerant: bar/EPSPS gene.

When it triggers

Question on which gene/strategy gives which trait.

How to avoid

Cry → insects. RNAi → nematodes. EPSPS → herbicide tolerance.

Trap

PCR vs blotting role confusion

Category: Similar Terms

PCR amplifies (makes copies); blotting transfers + visualises specific bands. Different stages of analysis.

When it triggers

Question asks which technique amplifies vs detects.

How to avoid

Amplify = PCR. Detect specific = blot (Southern DNA, Northern RNA, Western protein).

Trap

Restriction enzyme vs ligase vs polymerase

Category: Similar Terms

Restriction enzymes CUT at recognition sites; ligase JOINS sticky ends with phosphodiester bonds; polymerase synthesises strands.

When it triggers

Question asks which tool performs which step.

How to avoid

Cut = restriction. Paste = ligase. Copy = polymerase. Cohen-Boyer used EcoRI + ligase for first rDNA.

Past Year Questions

26 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2024

The following diagram shown restriction sites in E. coli cloning vector pBR322. Find the role of ‘X’ and ‘Y’ gens :

1The gene ‘X’ is responsible for resistance to antibiotics and ‘Y’ for protein involved in the replication of Plasmid.
2The gene ‘X’ is responsible for controlling the copy number of the linked DNA and ‘Y’ for protein involved in the replication of Plasmid.
3The gene ‘X’ is for protein involved in replication of Plasmid and ‘Y’ for resistance to antibiotics.
4Gene ’X’ is responsible for recognitions sites and ‘Y’ is responsible for antibiotic resistance
NTA Answer: Option 2(final)
NEET 2022

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Polymerase chain reaction is used in DNA amplification. Reason (R) : The ampicillin resistant gene is used as a selectable marker to check transformation In the light of the above statements, choose the correct answer from the options given below :

1(A) is not correct but (R) is correct
2Both (A) and (R) are correct and (R) is the correct explanation of (A)
3Both (A) and (R) are correct but (R) is not the correct explanation of (A)
4(A) is correct but (R) is not correct
NTA Answer: Option 3(final)
NEET 2022

Given below are two statements: Statement I: Restriction endonucleases recognise specific sequence to cut DNA known as palindromic nucleotide sequence. Statement II: Restriction endonucleases cut the DNA strand a little away from the centre of the palindromic site. In the light of the above statements, choose the most appropriate answer from the options given below:

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 2(final)
NEET 2020

¬˝ÁÃ’ œŸ ∞ ¡Êß◊Ê ∑ § Áfl ÿ ◊ ª‹Ã ∑§ÕŸ ∑§Ê ¬„øÊÁŸ∞– (4) After zygote formation

1Áø¬Áø¬ Á‚⁄ U «UË.∞Ÿ.∞. ‹Êߪ ¡ mÊ⁄UÊ ¡Ê «∏ ¡Ê ‚∑§Ã „Ò – 112. Identify the wrong statement with regard to Restriction Enzymes.
2¬˝àÿ ∑§ ¬˝ÁÃ’ œŸ ∞ ¡Êß◊ «UË.∞Ÿ.∞. ∑˝§◊ ∑§Ë ‹ê’Ê߸ ∑§Ê (1) Sticky ends can be joined by using DNA ÁŸ⁄UˡÊáÊ ∑§⁄U∑ § ∑§Êÿ¸ ∑§⁄Uà „Ò – ligases.
3ÿ «UË.∞Ÿ.∞. ∑§Ë ‹«∏Ë ∑§Ê ¬ÒÁ‹ã«˛UÊ Á◊∑§ SÕ‹Ê ¬⁄U (2) Each restriction enzyme functions by ∑§Ê≈Uà „Ò – inspecting the length of a DNA sequence. (3) They cut the strand of DNA at palindromic
4ÿ •ÊŸÈfl Á‡Ê∑§ ß ¡ËÁŸÿÁ⁄ Uª ◊ ©¬ÿÊ ªË „Ò – sites.
NTA Answer: Option 1(final)
NEET 2020

The sequence that controls the copy number of the 115. ∞∑§ fl Ä≈U⁄U ◊ ‚„‹ÇŸË «UË.∞Ÿ.∞. ∑§Ë ¬˝Áà ∑§Ë ‚ ÅÿÊ ∑§Ê linked DNA in the vector, is termed : ÁŸÿ ÁòÊà ∑§⁄UŸ flÊ‹ •ŸÈ∑˝§◊ ∑§Ê ÄÿÊ ∑§„Ê ¡ÊÃÊ „Ò?

1Recognition site (1) Á⁄U∑§ÊÚǟˇʟ (¬„øÊŸ) ‚Êß≈U
2Selectable marker
3Ori site (2) øÿŸÿÈÄà ◊Ê∑¸§⁄U
4Palindromic sequence (3) •Ê ⁄UË ‚Êß≈U (4) ¬Ò‹Ë «˛UÊ Á◊∑§ •ŸÈ∑˝§◊ 116. Name the enzyme that facilitates opening of DNA helix during transcription.
NTA Answer: Option 3(final)
NEET 2020

In gel electrophoresis, separated DNA fragments 124. ¡ ‹ ß‹ Ä≈˛UÊ »§Ê ⁄ UÁ‚‚ ◊ , ¬ÎÕ∑§ „È∞ «UË.∞Ÿ.∞. ∑ § πá«UÊ ∑§Ê can be visualized with the help of : Á∑§‚∑§Ë ‚„ÊÿÃÊ ‚ Œ πÊ ¡Ê ‚∑§ÃÊ „Ò?

1Ethidium bromide in infrared radiation (1) •fl⁄UÄà ÁflÁ∑§⁄UáÊ ◊ ∞ÁÕÁ«Uÿ◊ ’˝Ê ◊Êß«U ‚
2Acetocarmine in bright blue light (2) ø◊∑§Ë‹ ŸË‹ ¬˝∑§Ê‡Ê ◊ ∞ ‚Ë≈UÊ ∑§ÊÁ◊¸Ÿ ‚
3Ethidium bromide in UV radiation (3) UV ÁflÁ∑§⁄UáÊ ◊ ∞ÁÕÁ«Uÿ◊ ’˝Ê ◊Êß«U ‚
4Acetocarmine in UV radiation (4) UV ÁflÁ∑§⁄UáÊ ◊ ∞‚Ë≈UÊ ∑§ÊÁ◊¸Ÿ ‚
NTA Answer: Option 3(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Sources

NCERT refs: Class 12 Biology Chapter 11, p.236

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