CUET UG Biology Booster Test 3-Pest Resistance Technology -

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CUET UG Biology Booster Test 3-Pest Resistance Technology

⏱️ 30 Minutes

❓ 20 Questions

📌 Answers are locked once submitted — results and explanations appear at the end.

CUET UG Biology Booster Test 3-Pest Resistance Technology

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QUESTION 1 OF 20

Evaluate the biotechnological significance of Bacillus thuringiensis:
I. It provides an alternative to agro-chemical based agriculture by acting as a bio-pesticide.
II. Its application has entirely replaced the need for tissue culture in crop improvement.
III. The organism itself is directly sprayed onto crops as a chemical pesticide substitute in modern GM crop-based agriculture. Which statement(s) is/are deeply flawed based on the text?

Answer Review

1 Evaluate the biotechnological significance of Bacillus thuringiensis:
I. It provides an alternative to agro-chemical based agriculture by acting as a bio-pesticide.
II. Its application has entirely replaced the need for tissue culture in crop improvement.
III. The organism itself is directly sprayed onto crops as a chemical pesticide substitute in modern GM crop-based agriculture. Which statement(s) is/are deeply flawed based on the text?

A I only

B II and III only

C I and III only

D I, II, and III

💡 Short Explanation

Statement I is correct (it is an alternative bio-pesticide). Statement II is flawed (tissue culture is a separate technique still required for plant regeneration/transformation). Statement III is flawed (modern GM agriculture uses genes cloned in plants, not spraying the live bacterium).

✅ Correct Answer Explanation

Bt technology uses transgenic plants expressing specific genes, not the direct spraying of the bacterium (III). Furthermore, tissue culture remains an essential method for plant cell transformation and regeneration in biotechnology (II). Statement I is the only accurate reflection of the technology's primary purpose.

❓ Why Other Options Are Incorrect

Option A → Includes Statement I, which is accurate.
Option C → Includes Statement I, which is accurate.
Option D → Includes Statement I, which is accurate.

🎯 Strategy

Used: Elimination

Application: Identifying which statements are scientifically inaccurate based on NCERT biotechnology methods.

Final Logic: Only statement I is correct; II and III are flawed.

🧠 Memory Trick

"Bt = GM Plants, Not Sprays."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Cotton/General –

2 A research team is developing a new GM crop. Arrange the intricate steps of utilizing the Bt toxin gene:
1. Solubilisation in the pest's alkaline gut.
2. Expressing the gene in the host plant.
3. Cloning the gene.
4. Lysis of epithelial cells/mortality.

A 3, 2, 1, 4

B 2, 3, 1, 4

C 3, 1, 2, 4

D 2, 1, 3, 4

💡 Short Explanation

1. Cloning the gene. 1. Expressing the gene in the host plant. 1. Solubilisation in the pest's alkaline gut. 1. Lysis of epithelial cells/mortality.

✅ Correct Answer Explanation

The correct technological pipeline is: (3) Cloning the bacterial gene > (2) Incorporating and expressing it in the plant > (1) Ingestion by pest followed by alkaline solubilisation > (4) Final cell lysis and pest death.

❓ Why Other Options Are Incorrect

Options B, C, D → All misorder the sequence of genetic engineering (cloning/expression) relative to the biological activity (solubilisation/lysis).

🎯 Strategy

Used: Elimination

Application: Establishing the logical order of laboratory genetic engineering followed by pest physiology.

Final Logic: Engineering > Ingestion > Physiology.

🧠 Memory Trick

"Clone-Express-Solubilise-Lyse."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

3 Which of the following hypothetical scenarios involving Bt toxin specificity is NOT supported by the text?

A Using a Bt strain specific to lepidopterans to control an outbreak of armyworms.

B Utilizing a dipteran-specific Bt strain to target mosquito populations.

C Employing a coleopteran-specific Bt strain to eradicate a tobacco budworm infestation.

D Selecting different cry genes because most Bt toxins are insect-group specific.

💡 Short Explanation

Tobacco budworms are Lepidopterans. Coleopteran-specific strains will not affect Lepidopterans. This mismatch is not supported by the text.

✅ Correct Answer Explanation

Bt toxins are strictly group-specific. Tobacco budworms (Lepidopterans) require a Lepidopteran-specific toxin, not a Coleopteran-specific one. Therefore, Scenario C is scientifically incorrect according to the principle of target specificity.

❓ Why Other Options Are Incorrect

Option A → Armyworms are Lepidopterans; this is a valid application.
Option B → Mosquitoes are Dipterans; this is a valid application.
Option D → This is a true statement regarding Bt technology.

🎯 Strategy

Used: Substitution

Application: Identifying the mismatched order-pest relationship.

Final Logic: Wrong order = No effect.

🧠 Memory Trick

"Match Order to Pest."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Specificity –

4 If an agricultural biotechnology firm develops a GM crop incorporating only toxins strictly specific to dipterans, which of the following pests will definitively continue to ravage the crop unaffected?

A Flies

B Mosquitoes

C Coleopteran beetles

D Both A and B

💡 Short Explanation

Dipteran-specific toxin kills flies/mosquitoes. It does NOT kill Coleopterans (beetles). Therefore, beetles will survive.

✅ Correct Answer Explanation

Because Bt toxins are order-specific, a crop expressing only a dipteran-specific toxin is immune to Dipterans (flies/mosquitoes) but remains susceptible to pests of other orders, such as Coleopteran beetles.

❓ Why Other Options Are Incorrect

Option A → Flies would be killed.
Option B → Mosquitoes would be killed.
Option D → Both would be killed, so they would not "ravage the crop."

🎯 Strategy

Used: Elimination

Application: Identifying which pest does not belong to the Diptera order.

Final Logic: Non-Dipteran = Unaffected.

🧠 Memory Trick

"Dipteran $\neq$ Coleopteran."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Specificity –

5 From a developmental biology perspective of B. thuringiensis, if a mutation prevented the bacterium from entering the "particular phase of their growth" mentioned in the text, what would be the most immediate biotechnological consequence?

A The bacteria would immediately die due to autotoxicity.

B The formation of protein crystals containing the toxic insecticidal protein would not occur.

C The bacteria would permanently express the active form of the toxin.

D The alkaline pH of the bacteria's internal environment would increase.

💡 Short Explanation

Crystals are formed only during a specific growth phase. No phase = No crystals. No crystals = No bio-pesticide.

✅ Correct Answer Explanation

The synthesis of the crystalline insecticidal protein is developmentally regulated to occur only during a specific growth phase. If this phase is blocked, the protein crystals will not be synthesized, rendering the bacterium useless for Bt-based pesticide production.

❓ Why Other Options Are Incorrect

Option A → The bacteria might still survive; they just wouldn't make the protein.
Option C → The toxin is produced as a protoxin, not an active toxin.
Option D → The growth phase mutation does not directly dictate internal pH.

🎯 Strategy

Used: Substitution

Application: Correlating the "phase" requirement with the "crystal" result.

Final Logic: No phase > No crystal.

🧠 Memory Trick

"Phase = Trigger for Crystal."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

6 Match the functional states/locations of the insecticidal protein to their corresponding descriptions:

Column I	Column II
1. In bacterium	i. Exists as inactive protoxin
2. In crystal	ii. Solubilised/activated
3. In gut	iii. Binds/creates pores
4. On midgut epithelium	iv. Formed during growth phase

A 1-iv, 2-i, 3-ii, 4-iii

B 1-i, 2-iv, 3-iii, 4-ii

C 1-iv, 2-ii, 3-i, 4-iii

D 1-ii, 2-i, 3-iv, 4-iii

💡 Short Explanation

1 (In bacterium) = Formed during growth phase (iv). 2 (In crystal) = Exists as inactive protoxin (i). 3 (In gut) = Solubilised/activated (ii). 4 (On midgut epithelium) = Binds/creates pores (iii).

✅ Correct Answer Explanation

The protein progresses through a life-cycle: it is synthesized during a growth phase (1-iv), packaged as an inactive protoxin crystal (2-i), solubilised by the alkaline gut (3-ii), and then performs its final function by binding and causing cell lysis (4-iii).

❓ Why Other Options Are Incorrect

Options B, C, D → Misalign the biological states with their descriptions.

🎯 Strategy

Used: Option Grouping

Application: Matching the developmental stages of the Bt protein to their specific roles.

Final Logic: Correct chronological matching.

🧠 Memory Trick

"Grow-Protoxin-Solubilise-Lyse."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

7 Analyse the biochemical transition of the Bt toxin:
I. The protoxin requires a highly acidic environment to cleave into its active form.
II. The active form of the toxin is inherently unstable and breaks down before reaching the midgut.
III. The protoxin's inactivity is the primary reason the Bacillus survives its own toxic production. Which of the analytical statements is correct?

A I only

B III only

C II and III only

D I and II only

💡 Short Explanation

Statement I is incorrect: It requires an alkaline (not acidic) environment. Statement II is incorrect: The toxin is stable until it binds. Statement III is correct: Inactivity (protoxin) protects the bacterium.

✅ Correct Answer Explanation

The inactive protoxin state (III) is essential for bacterial survival. Statement I is false because the gut is alkaline, and Statement II is false because the toxin is stable enough to reach the target receptor.

❓ Why Other Options Are Incorrect

Options A, C, D → These include statements (I or II) that are scientifically incorrect.

🎯 Strategy

Used: Elimination

Application: Filtering out the incorrect chemical trigger (Acidic) and the incorrect stability claim.

Final Logic: Only III is biologically sound.

🧠 Memory Trick

"Only III is true."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

8 A new species of pest is discovered that possesses a highly acidic digestive tract. If this pest ingests tissues from a standard Bt cotton plant, what is the most scientifically sound prediction based on the text?

A The crystals will solubilise rapidly, killing the pest faster than usual.

B The inactive protoxins will remain insoluble and inactive, leaving the pest unharmed.

C The acidic pH will convert the protoxin directly into dsRNA.

D The plant will undergo RNA interference to compensate for the pH difference.

💡 Short Explanation

Bt toxin requires an alkaline pH to become active. Acidic pH will not solubilise the crystals. The pest will survive.

✅ Correct Answer Explanation

Bt toxins rely on the high alkaline pH of the pest's midgut to solubilise the crystals and activate the protoxin. If the pest lacks an alkaline gut, the protoxin remains in its inactive, crystalline form, and no injury occurs to the pest.

❓ Why Other Options Are Incorrect

Option A → Acidic pH does not activate it.
Option C → Acid does not produce dsRNA.
Option D → RNAi is a different, separate mechanism.

🎯 Strategy

Used: Substitution

Application: Applying the "Alkaline = Active" rule to an "Acidic" condition.

Final Logic: No Alkaline = No Activation.

🧠 Memory Trick

"Acidic = Safe for Pest."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

9 Which of the following is NOT a sequential downstream effect of the activated toxin successfully binding to the surface of midgut epithelial cells?

A Creation of pores in the cell membrane

B Swelling of the epithelial cells

C Conversion of active toxin back into inactive protoxin crystals

D Eventual lysis of the cells and death of the insect

💡 Short Explanation

Once active, the toxin does not revert to a protoxin. It proceeds to create pores and cause cell death. Statement C is not a sequential effect.

✅ Correct Answer Explanation

After binding, the toxin causes pore formation (A), which triggers osmotic swelling (B) and cell death (D). There is no biological mechanism for the toxin to "revert" to an inactive protoxin once it has been activated.

❓ Why Other Options Are Incorrect

Options A, B, D → These are all valid consequences of toxin binding.

🎯 Strategy

Used: Elimination

Application: Identifying the step that is biologically impossible in the Bt toxin cycle.

Final Logic: Activation is an irreversible step.

🧠 Memory Trick

"Once Active, Always Active."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

10 At a cellular level, how does the pore formation induced by Bt toxin ultimately lead to the insect's death?

A By causing an uncontrolled influx/efflux that leads to cell swelling and physical rupture (lysis).

B By directly silencing the insect's vital mRNA via RNA interference.

C By neutralizing the alkaline pH of the gut, halting digestion.

D By blocking the insect's respiratory spiracles.

💡 Short Explanation

Pores disrupt membrane integrity. Water rushes in (swelling). Cells burst (lysis). This leads to death.

✅ Correct Answer Explanation

Pores in the cell membrane destroy the cell's osmotic integrity. Water influx causes the cells to swell, and they eventually rupture (lyse), destroying the midgut and leading to the insect's death.

❓ Why Other Options Are Incorrect

Option B → Silencing mRNA is RNAi, not Bt toxin action.
Option C → The toxin doesn't neutralize pH.
Option D → The toxin affects the gut, not the respiratory system directly

🎯 Strategy

Used: Substitution

Application: Explaining the physical consequence of pore formation.

Final Logic: Pore > Lysis > Death.

🧠 Memory Trick

"Pore = Swell = Burst."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt Toxin Mechanism –

11 When isolating specific Bt genes for incorporation into crops, a researcher must make careful choices. Which of the following assumptions would lead to a FAILED crop protection based on the text?

A Assuming the choice of gene depends on the targeted pest.

B Assuming most Bt toxins are insect-group specific.

C Assuming cryIAb will effectively control cotton bollworms.

D Assuming the choice of gene depends on the crop itself.

💡 Short Explanation

cryIAb is specific to the corn borer. Cotton bollworms are targeted by cryIAc and cryIIAb. Therefore, assuming cryIAb works for bollworms is a failure.

✅ Correct Answer Explanation

Bt toxins are highly insect-group specific. cryIAb is the correct gene for corn borer, while cotton bollworms require cryIAc or cryIIAb. Using the wrong gene will result in the pest remaining unaffected, leading to a failed .

❓ Why Other Options Are Incorrect

Option A → This is a correct assumption for .
Option B → This is the fundamental principle of Bt specificity.
Option D → While the crop is the host, the gene is chosen based on the pest (which usually attacks that crop).

🎯 Strategy

Used: Substitution

Application: Identifying the incorrect gene-pest mapping.

Final Logic: Wrong Gene = No Protection.

🧠 Memory Trick

"IAb = Corn, IAc = Cotton."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Cry Genes Table –

12 Match the genetically modified biotechnological application to its underlying cellular mechanism/feature:

Column I	Column II
1. Bt Cotton	i. cry gene expression
2. Nematode-resistant Tobacco	ii. Vitamin A enrichment
3. Golden Rice	iii. RNAi
4. Transgenic models	iv. Disease studies

A 1-i, 2-iii, 3-ii, 4-iv

B 1-iii, 2-i, 3-iv, 4-ii

C 1-i, 2-iv, 3-iii, 4-ii

D 1-ii, 2-i, 3-iii, 4-iv

💡 Short Explanation

Bt Cotton (1) = cry gene expression (i). Nematode-resistant Tobacco (2) = RNAi (iii). Golden Rice (3) = Vitamin A enrichment (ii). Transgenic models (4) = Disease studies (iv).

✅ Correct Answer Explanation

Bt cotton uses cry genes for insect resistance. Nematode-resistant tobacco uses the RNAi mechanism to silence parasitic genes. Golden Rice is engineered for Vitamin A enrichment. Transgenic models serve as tools to study the genetic basis of disease development.

❓ Why Other Options Are Incorrect

Options B, C, D → All mismatch the biotech application with its corresponding scientific principle.

🎯 Strategy

Used: Option Grouping

Application: Linking applications to their core biotechnological mechanisms.

Final Logic: Correct mapping of biotech application to its mechanism.

🧠 Memory Trick

"Bt-Cry, Tobacco-RNAi, Rice-VitA."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Various Applications – –201

13 If a transgenic cotton plant is engineered expressing only the cryIAc gene, which of the following pests will experience midgut epithelial cell lysis upon ingesting the plant?

A Corn borer

B Cotton bollworms

C Nematodes

D Dipterans

💡 Short Explanation

cryIAc is specific to cotton bollworms. Lysis is the mechanism of the toxin. The bollworm ingesting it will suffer lysis.

✅ Correct Answer Explanation

The cryIAc gene encodes a protein toxic to cotton bollworms. When the bollworm ingests the transgenic plant tissue, the toxin is activated and binds to the midgut, leading to cell lysis and death. It does not affect corn borers, nematodes, or dipterans.

❓ Why Other Options Are Incorrect

Option A → Corn borers require cryIAb.
Option C → Nematodes are not affected by Bt toxins.
Option D → Dipterans require dipteran-specific toxins.

🎯 Strategy

Used: Substitution

Application: Mapping the gene (cryIAc) to its target pest (Bollworm).

Final Logic: Gene-Pest match.

🧠 Memory Trick

"IAc = Bollworm."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Cry Genes Table –

14 Which of the following genetic engineering combinations is NOT correctly matched to achieve successful pest resistance?

A cryIAc incorporated into cotton -> Resistance against cotton bollworms

B cryIIAb incorporated into cotton -> Resistance against cotton bollworms

C cryIAb incorporated into corn -> Resistance against corn borer

D cryIAb incorporated into cotton -> Resistance against nematodes

💡 Short Explanation

cryIAb is for corn borer, not nematodes. Nematodes are resistant to Bt, they require RNAi. Option D is an incorrect application.

✅ Correct Answer Explanation

Bt genes (cry) only work on insects. Nematodes require the RNAi mechanism for control. Pairing cryIAb with nematodes is a conceptual error as it ignores the taxonomic difference between insects and nematodes.

❓ Why Other Options Are Incorrect

Options A, B, C → All these are correct mappings according to the NCERT table.

🎯 Strategy

Used: Elimination

Application: Identifying the incorrect application of technology (Bt vs Nematodes).

Final Logic: Bt = Insects; RNAi = Nematodes.

🧠 Memory Trick

"Nematodes $\neq$ Bt."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: Bt vs RNAi –

📄 Passage

"Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant. The introduction of DNA was such that it produced both sense and anti-sense RNA in the host cells. These two RNA's being complementary to each other formed a double stranded (dsRNA) that initiated RNAi and thus, silenced the specific mRNA of the nematode. The consequence was that the parasite could not survive in a transgenic host expressing specific interfering RNA."

Based on the passage, what is the ultimate analytical reason the parasite (Meloidegyne incognitia) fails to survive in the transgenic host?

A The host plant secretes toxic protein crystals into the soil.

B The expression of specific interfering RNA in the host plant compromises the nematode's vital mRNA translation.

C The Agrobacterium vectors aggressively attack the nematode's nervous system.

D The sense RNA directly degrades the nematode's DNA.

💡 Short Explanation

Passage states RNAi "silenced the specific mRNA of the nematode." mRNA silencing blocks translation. The parasite dies because it cannot produce vital proteins.

✅ Correct Answer Explanation

The transgenic host produces dsRNA, which triggers the RNA interference pathway. This process targets the parasite's specific mRNA, preventing its translation into proteins essential for the nematode's survival, thereby killing it.

❓ Why Other Options Are Incorrect

Option A → Bt crystals are not used for nematodes.
Option C → Agrobacterium is a delivery tool, not a killer.
Option D → RNAi affects translation (mRNA), not the DNA itself.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Extracting the mechanism of action from the passage provided.

Final Logic: mRNA Silencing = Translation Block.

🧠 Memory Trick

"mRNA Silencing = Protein Block."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Mechanism –

📄 Passage

According to the passage, the specific genetic architecture of the DNA introduced into the tobacco plant was purposely designed to:

A Mutate the host plant's apical meristem.

B Produce solely anti-sense RNA to attack the nematode.

C Produce both sense and anti-sense RNA simultaneously to ensure dsRNA formation.

D Alter the alkaline pH of the tobacco root cells.

💡 Short Explanation

Passage states: "it produced both sense and anti-sense RNA... formed a double stranded (dsRNA)." This is the design requirement for the DNA.

✅ Correct Answer Explanation

The passage explicitly explains that the DNA was introduced to produce both sense and anti-sense RNA, which are complementary and hybridize to form the dsRNA necessary to trigger the RNA interference process.

❓ Why Other Options Are Incorrect

Option A → Mutations are not the goal.
Option B → Solely anti-sense is insufficient for dsRNA.
Option D → pH alteration is not part of the RNAi mechanism.

🎯 Strategy

Used: Contextual/Tonal Matching

Application: Directly identifying the design requirement stated in the passage.

Final Logic: Sense + Anti-sense = dsRNA.

🧠 Memory Trick

"Sense + Anti-sense = Design Goal."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Methodology –

17 In the natural cellular defense mechanisms of eukaryotic organisms, what can serve as the source of the complementary RNA that triggers RNA interference?

A Infection by viruses having DNA genomes exclusively

B Infection by viruses having RNA genomes or mobile genetic elements (transposons)

C The spontaneous breakdown of the cell's own rough endoplasmic reticulum

D Ingestion of inactive protoxin crystals

💡 Short Explanation

The text defines RNAi as a defense against viral RNA and transposons. DNA viruses are not the primary trigger. ER breakdown and protoxin ingestion are irrelevant.

✅ Correct Answer Explanation

RNAi is an ancient defense system. Natural triggers include RNA viruses (which use dsRNA intermediates) and transposable elements (mobile genetic elements) that can cause genomic instability.

❓ Why Other Options Are Incorrect

Option A → DNA viruses are not the sole or primary target as described.
Option C → ER breakdown is unrelated to RNAi defense.
Option D → Protoxins relate to Bt bacteria, not RNAi.

🎯 Strategy

Used: Substitution

Application: Recalling the natural triggers of RNAi from the NCERT text.

Final Logic: RNAi defends against viral RNA and transposons.

🧠 Memory Trick

"RNA Virus + Transposons = Triggers."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Mechanism –

18 Analytically speaking, if the complementary dsRNA molecule successfully binds during RNA interference, which central dogma process of the nematode is directly blocked?

A DNA Replication

B Transcription of DNA to mRNA

C Translation of mRNA into protein

D Reverse transcription

💡 Short Explanation

Silencing mRNA means the mRNA cannot be used for protein synthesis. Protein synthesis is "Translation." Therefore, Translation is blocked.

✅ Correct Answer Explanation

The dsRNA binds to the mRNA, effectively masking or degrading it. Since mRNA is the template for protein synthesis, the process of translation is directly blocked. The nematode, lacking essential proteins, dies.

❓ Why Other Options Are Incorrect

Option A → Replication is DNA-to-DNA.
Option B → Transcription is DNA-to-mRNA (this is not the step blocked by mRNA binding).
Option D → Reverse transcription is RNA-to-DNA.

🎯 Strategy

Used: Substitution

Application: Identifying the step in the Central Dogma that mRNA acts upon.

Final Logic: mRNA > Protein (Translation).

🧠 Memory Trick

"mRNA Silencing = Translation Stop."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Mechanism –

19 A laboratory attempts to use Agrobacterium vectors to create nematode resistance but inadvertently constructs the vector so that it only produces sense RNA in the host cells. What is the predicted analytical outcome?

A RNAi will initiate normally as sense RNA is sufficient for silencing.

B RNAi will fail to initiate because the complementary anti-sense RNA is missing, meaning no dsRNA is formed.

C The host plant will become highly toxic to lepidopteran pests instead.

D The Agrobacterium will infect the nematode directly.

💡 Short Explanation

RNAi requires double-stranded RNA (dsRNA). Sense alone is single-stranded. No dsRNA = No trigger.

✅ Correct Answer Explanation

RNAi strictly requires a double-stranded trigger (dsRNA). If only sense RNA is produced, the RNA remains single-stranded and cannot form the necessary dsRNA structure to initiate the silencing pathway, leading to a total failure of the resistance .

❓ Why Other Options Are Incorrect

Option A → Single-stranded RNA does not trigger RNAi.
Option C → Lepidopteran toxicity requires Bt toxins, not single-stranded RNA.
Option D → Agrobacterium is not a nematode pathogen.

🎯 Strategy

Used: Elimination

Application: Applying the "dsRNA" requirement to a scenario with only one strand.

Final Logic: No dsRNA = No RNAi.

🧠 Memory Trick

"Single-stranded $\neq$ RNAi."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Methodology –

20 Map the complex molecular cascade of RNAi from vector insertion to parasite death:
1. Silencing of mRNA.
2. Introduction of DNA.
3. Death of parasite.
4. Formation of dsRNA.

A 2, 4, 1, 3

B 2, 1, 4, 3

C 4, 2, 1, 3

D 2, 4, 3, 1

💡 Short Explanation

1. Introduction of DNA. 1. Formation of dsRNA. 1. Silencing of mRNA. 1. Death of parasite.

✅ Correct Answer Explanation

The correct sequence: (2) DNA is introduced into the plant via Agrobacterium vectors > (4) Sense/Anti-sense strands form the dsRNA > (1) dsRNA silences the parasite's vital mRNA > (3) Parasite cannot translate vital proteins and dies.

❓ Why Other Options Are Incorrect

Options B, C, D → Misorder the steps of transformation, molecular triggering, silencing, and parasite death.

🎯 Strategy

Used: Substitution

Application: Ordering the biotechnological cascade.

Final Logic: DNA > dsRNA > Silencing > Death.

🧠 Memory Trick

"Insert-dsRNA-Silence-Die."

📚 Class XII – Biology – Chapter: Biotechnology and its Applications – Topic: RNAi Methodology –

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