101. Which statement best explains why different cry genes are used in different transgenic crops?
ⓐ. All cry genes act equally on every insect pest.
ⓑ. cry genes are selected mainly on the basis of flower color.
ⓒ. A single cry gene can protect every crop from all pathogens.
ⓓ. Different cry genes show specificity toward different target insects.
Correct Answer: Different cry genes show specificity toward different target insects.
Explanation: Bt toxins are not universally effective against all insect pests. Different cry genes produce toxin proteins that act on particular insect groups or species. Gene choice therefore depends on the target pest present in the crop. Pest specificity is one of the most important features of Bt technology.
102. Which cry gene is commonly associated with protection against corn borer?
ⓐ. cryAII
ⓑ. cryIAc
ⓒ. cryIIAb
ⓓ. cryIAb
Correct Answer: cryIAb
Explanation: cryIAb is the Bt gene commonly linked with resistance against corn borer. It is different from cryIAc and cryIIAb, which are associated with control of cotton bollworms. This distinction shows that Bt genes are chosen according to pest target. Mixing up these gene-pest matches is a common error.
103. Which target pest is most closely associated with the use of cryIAc and cryIIAb?
ⓐ. Root-knot nematode
ⓑ. Corn borer
ⓒ. Cotton bollworms
ⓓ. Aphid population
Correct Answer: Cotton bollworms
Explanation: cryIAc and cryIIAb are the standard Bt genes associated with control of cotton bollworms. These genes help the plant produce toxins that affect the target insect after ingestion. The pairing is specific and should not be interchanged with the gene used for corn borer. Accurate gene-pest mapping is essential in Bt-based crop design.
104. Which statement about Bt gene selection is correct?
ⓐ. The same Bt gene is used in every crop regardless of pest.
ⓑ. The choice of cry gene depends on the crop and the target pest.
ⓒ. Bt genes are selected only according to plant height.
ⓓ. cry genes are useful only in bacterial cultures, not in crops.
Correct Answer: The choice of cry gene depends on the crop and the target pest.
Explanation: Bt-based resistance works well only when the correct gene is chosen for the intended insect pest. Since different cry genes act on different target insects, crop protection requires specific matching. The crop system and pest type are both important. Gene choice is therefore purposeful rather than random.
105. Fill in the blank in the most accurate way:
A Bt crop designed mainly to control corn borer would most appropriately contain the gene ______.
ⓐ. cryIAb
ⓑ. cryIAc
ⓒ. cryIIAb
ⓓ. cryIIIA
Correct Answer: cryIAb
Explanation: cryIAb is the Bt gene classically associated with control of corn borer. It is therefore the correct choice when the target pest is corn borer rather than cotton bollworm. The other commonly discussed genes, cryIAc and cryIIAb, are linked with bollworm control.
106. Which option correctly compares the use of cryIAc and cryIIAb with cryIAb?
ⓐ. cryIAc and cryIIAb are both used mainly for drought tolerance, while cryIAb improves nutrition.
ⓑ. cryIAc and cryIIAb are used for virus resistance, while cryIAb controls fungi.
ⓒ. cryIAc and cryIIAb are used for post-harvest protection, while cryIAb improves mineral use.
ⓓ. cryIAc and cryIIAb are linked with cotton bollworms, while cryIAb is linked with corn borer.
Correct Answer: cryIAc and cryIIAb are linked with cotton bollworms, while cryIAb is linked with corn borer.
Explanation: This comparison highlights the pest specificity of Bt genes. cryIAc and cryIIAb are associated with control of cotton bollworms, whereas cryIAb is associated with corn borer. The distinction is based on biological target, not on general crop improvement. Each gene is selected for the pest it is most suitable against.
107. RNA interference is best described as a process in which
ⓐ. proteins are directly melted inside host cells
ⓑ. specific mRNA is silenced by a complementary RNA mechanism
ⓒ. DNA is removed permanently from every chromosome
ⓓ. insects are killed by alkaline gut toxins
Correct Answer: specific mRNA is silenced by a complementary RNA mechanism
Explanation: RNA interference, or RNAi, is a cellular mechanism that suppresses expression of a specific gene. It works through double-stranded RNA that matches a target mRNA and leads to its silencing. Because the mRNA is neutralized, the corresponding protein is not produced properly.
108. In the biotechnology example involving tobacco, which parasite is controlled through RNA interference?
ⓐ. cotton bollworm
ⓑ. corn borer
ⓒ. Meloidogyne incognita
ⓓ. rice weevil
Correct Answer: Meloidogyne incognita
Explanation: Meloidogyne incognita is a root-knot nematode that parasitizes tobacco roots and reduces yield. RNA interference is used here as a targeted defense strategy against this parasite.
109. Which statement correctly identifies the biological role of RNA interference in eukaryotic cells?
ⓐ. It converts bacterial protoxin into active toxin.
ⓑ. It activates every mRNA present in the cytoplasm.
ⓒ. It acts as a defense mechanism by silencing specific RNA molecules.
ⓓ. It promotes pollination in flowering plants.
Correct Answer: It acts as a defense mechanism by silencing specific RNA molecules.
Explanation: RNA interference functions as a protective regulatory mechanism in eukaryotic cells. By using complementary RNA to target a specific mRNA, it prevents that message from functioning normally. This reduces or blocks synthesis of the corresponding protein.
110. In RNA interference, double-stranded RNA is important because it
ⓐ. strengthens the cell wall of the host plant
ⓑ. activates insect digestion in alkaline medium
ⓒ. joins with bacterial plasmids to form seeds
ⓓ. triggers silencing of the matching mRNA sequence
Correct Answer: triggers silencing of the matching mRNA sequence
Explanation: Double-stranded RNA is the key signal that initiates RNA interference. When it corresponds to a particular mRNA sequence, the cellular machinery recognizes the match and suppresses that message. As a result, the related protein cannot be produced effectively. This sequence-based silencing is what makes RNAi highly specific.
111. In the RNA interference strategy used to protect tobacco plants, Agrobacterium mainly acts as
ⓐ. a source of Bt protoxin for insect control
ⓑ. a vector to introduce specific gene sequences into plant cells
ⓒ. a nutrient supplier for nematode growth
ⓓ. an enzyme that directly destroys parasite proteins
Correct Answer: a vector to introduce specific gene sequences into plant cells
Explanation: Agrobacterium is commonly used as a gene-delivery system in plant biotechnology. Here it introduces nematode-specific gene sequences into tobacco cells so the plant can produce the RNA molecules needed for RNA interference.
112. In RNA interference-based resistance, production of both sense and antisense RNA in the host cell leads to formation of
ⓐ. single-stranded DNA
ⓑ. active Bt toxin
ⓒ. complementary proteins
ⓓ. double-stranded RNA
Correct Answer: double-stranded RNA
Explanation: Sense and antisense RNA strands are complementary to each other. When both are produced in the same cell, they pair together to form double-stranded RNA. This double-stranded RNA is the trigger for the RNA interference pathway. The process does not create protein or DNA at this stage.
113. Which event directly triggers RNA interference in the transgenic host plant?
ⓐ. Formation of double-stranded RNA from complementary RNA strands
ⓑ. Fusion of two protoplasts from unrelated species
ⓒ. Removal of the plant cell wall to form protoplasts
ⓓ. Binding of Bt toxin to insect midgut cells
Correct Answer: Formation of double-stranded RNA from complementary RNA strands
Explanation: The key initiating signal for RNA interference is the presence of double-stranded RNA. This molecule is recognized by the cell as a target for gene-silencing machinery. Once the pathway is activated, the matching mRNA is degraded or suppressed. Without double-stranded RNA, the RNAi response does not begin effectively.
114. In the RNA interference approach against root-knot nematode, which molecule is ultimately silenced?
ⓐ. host plant chloroplast DNA
ⓑ. bacterial plasmid RNA
ⓒ. nematode-specific mRNA
ⓓ. plant ribosomal subunit
Correct Answer: nematode-specific mRNA
Explanation: The RNAi strategy is designed so that the double-stranded RNA matches a specific mRNA of the nematode parasite. When the parasite interacts with the host, that matching mRNA becomes the target of silencing. As a result, the corresponding protein cannot be produced properly in the nematode. This selective silencing helps protect the plant without broadly damaging host functions.
115. Why does RNA interference-based resistance help protect the host plant from Meloidogyne incognita?
ⓐ. The plant releases antibodies into the soil around the roots.
ⓑ. Essential gene expression in the nematode is blocked by mRNA silencing.
ⓒ. The transgenic plant becomes too hard for the nematode to penetrate.
ⓓ. The roots begin producing alkaline fluid that activates protoxin.
Correct Answer: Essential gene expression in the nematode is blocked by mRNA silencing.
Explanation: RNA interference disrupts gene expression by preventing the target mRNA from functioning. When this happens in the nematode, important proteins needed for its survival or parasitic activity cannot be formed normally. The parasite therefore fails to establish itself successfully on the host plant. Protection comes from gene silencing, not from hardness of tissue or antibody production.
116. Which statement best distinguishes RNA interference from Bt-based pest resistance?
ⓐ. RNA interference works only in bacteria, whereas Bt works only in fungi.
ⓑ. RNA interference depends on seed dormancy, whereas Bt depends on pollination.
ⓒ. RNA interference improves only mineral-use efficiency, whereas Bt improves only nutrition.
ⓓ. RNA interference silences specific mRNA, whereas Bt acts through toxin-mediated gut damage.
Correct Answer: RNA interference silences specific mRNA, whereas Bt acts through toxin-mediated gut damage.
Explanation: RNA interference and Bt technology are both used for pest protection, but their mechanisms are very different. RNAi is based on sequence-specific suppression of target mRNA, whereas Bt protection depends on an insecticidal protein that damages the gut lining of the pest. One acts at the level of gene expression, and the other acts through a toxin.
117. A transgenic tobacco plant has been engineered to produce both sense and antisense RNA for a nematode gene. The most immediate molecular outcome in the plant cells will be
ⓐ. pairing of the two RNA strands to form double-stranded RNA
ⓑ. rapid synthesis of mature insulin in the roots
ⓒ. conversion of all plant mRNA into DNA copies
ⓓ. elimination of all microorganisms from the rhizosphere
Correct Answer: pairing of the two RNA strands to form double-stranded RNA
Explanation: When sense and antisense transcripts of the same sequence are produced together, they base-pair with one another. This forms double-stranded RNA, the trigger required for RNA interference.
118. Root-knot disease in tobacco caused by Meloidogyne incognita mainly reduces crop yield because the parasite
ⓐ. destroys flowers by feeding on pollen grains
ⓑ. infects leaf epidermis and blocks stomata
ⓒ. parasitises the roots and interferes with normal plant function
ⓓ. consumes stored seeds before germination
Correct Answer: parasitises the roots and interferes with normal plant function
Explanation: Meloidogyne incognita is a root parasite, so its harmful effect begins below the soil surface. By attacking the roots, it disrupts normal uptake and overall plant performance, which leads to reduced yield. The damage is not primarily through pollen destruction or leaf infection. Its root-based parasitic habit is the reason it is such a serious problem.
119. Which sequence best represents the RNA interference strategy used for nematode resistance in tobacco?
ⓐ. Infect plant with nematode → isolate toxin → clone bacterium → kill roots
ⓑ. Remove cell walls → fuse protoplasts → regenerate hybrid plant → test fertility
ⓒ. Insert Bt gene → produce protoxin → activate in alkaline gut → kill insect
ⓓ. Insert target sequence → make sense and antisense RNA → form dsRNA → silence nematode mRNA
Correct Answer: Insert target sequence → make sense and antisense RNA → form dsRNA → silence nematode mRNA
Explanation: In this strategy, selected gene sequences are first introduced into the plant. The plant then produces both sense and antisense RNA, which pair to form dsRNA and trigger silencing of the matching nematode mRNA.
120. Which statement about RNA interference-based plant protection is correct?
ⓐ. It works by making all RNA in the host plant inactive.
ⓑ. It protects the host by silencing a specific matching mRNA sequence.
ⓒ. It depends on antibody production against the nematode.
ⓓ. It kills the parasite through direct secretion of bacterial endotoxin.
Correct Answer: It protects the host by silencing a specific matching mRNA sequence.
Explanation: RNA interference is precise because it targets only RNA sequences that are complementary to the double-stranded RNA trigger. This specificity allows the plant to interfere with expression of selected parasite genes rather than shut down all RNA activity. The mechanism is not based on antibodies or bacterial toxins.
