101. A farmer decides to manage crop pests by using living organisms and naturally occurring biological interactions instead of relying mainly on synthetic pesticides. This approach is best described as
ⓐ. sewage treatment
ⓑ. biofertilisation
ⓒ. biological control
ⓓ. industrial fermentation
Correct Answer: biological control
Explanation: Biocontrol refers to the use of biological methods for controlling plant diseases and pests. Instead of depending primarily on toxic chemical pesticides, biocontrol makes use of natural enemies, microbial agents and ecological interactions that can keep harmful organisms under control. The important idea is not simply that a living organism is present, but that biological relationships are deliberately used to manage pests or pathogens. This makes biocontrol fundamentally different from biofertilisation, whose main purpose is to improve soil nutrient quality rather than suppress pests.
102. One major reason for reducing excessive dependence on conventional insecticides and pesticides is that these chemicals
ⓐ. always increase the diversity of beneficial organisms
ⓑ. may be toxic to humans, livestock and other animals
ⓒ. can act only against weeds and never against insects
ⓓ. automatically improve groundwater quality
Correct Answer: may be toxic to humans, livestock and other animals
Explanation: Conventional chemical pesticides can control agricultural pests effectively, but their use may also create harmful effects beyond the intended target organisms. Some of these chemicals can be toxic to humans and animals, especially when exposure occurs through contaminated food, water or the agricultural environment. This is one reason biological control methods are environmentally attractive. Biocontrol aims to manage pest populations while reducing the broad toxic effects that can accompany indiscriminate or excessive chemical use.
103. Repeated application of agricultural pesticides and weedicides can create environmental problems because such chemicals may
ⓐ. remain restricted only to the body of the target pest
ⓑ. convert groundwater into nutrient-rich irrigation water
ⓒ. contaminate soil, groundwater and agricultural produce
ⓓ. increase the population of every beneficial organism
Correct Answer: contaminate soil, groundwater and agricultural produce
Explanation: Agricultural chemicals do not necessarily remain confined to the organisms against which they are applied. Residues can enter soil, groundwater and food materials such as fruits, vegetables and other crops. Weedicides can also contribute to soil pollution. The environmental concern therefore extends beyond immediate pest killing. This broader contamination risk supports the use of biological control strategies that rely more on ecological interactions and target-specific biological agents.
104. In a crop field, a predatory insect naturally feeds on an agricultural pest and prevents the pest population from increasing beyond damaging levels. This situation illustrates
ⓐ. industrial production of a microbial toxin
ⓑ. predation operating as biological control
ⓒ. conversion of a pest into a biofertiliser
ⓓ. chemical eradication of an unwanted organism
Correct Answer: predation operating as biological control
Explanation: Natural predation is an important ecological basis of biological control. A predator feeds on a pest species and helps regulate its population without the need for indiscriminate chemical killing. The goal is usually not to eliminate every individual pest but to prevent the population from reaching levels that cause serious crop damage. This approach uses an existing ecological interaction as a management tool and therefore fits the basic principle of biocontrol.
105. An organic farmer aims to maintain a biologically diverse field ecosystem rather than eliminate every insect that feeds on crops. Why can this strategy support long-term pest management?
ⓐ. Greater ecological diversity can support natural regulatory interactions that keep pests at manageable levels
ⓑ. Every organism in a diverse ecosystem becomes a crop pest
ⓒ. Greater ecological diversity cannot support natural regulatory interactions that keep pests at manageable levels
ⓓ. Diverse ecosystems eliminate the need for any knowledge of pest biology
Correct Answer: Greater ecological diversity can support natural regulatory interactions that keep pests at manageable levels
Explanation: Organic farming and biological control are based on the idea that a healthy agricultural ecosystem contains many interacting organisms. Predators, parasites and other beneficial species can naturally restrict pest populations. Maintaining biodiversity helps preserve these ecological relationships, making pest regulation more sustainable. The objective is generally to maintain pests below damaging levels rather than to create a biologically empty field in which every non-crop organism has been eliminated.
106. Complete eradication of a pest population from an agricultural ecosystem may sometimes be undesirable because
ⓐ. pests are always needed for nitrogen fixation
ⓑ. pest removal necessarily increases soil phosphorus levels
ⓒ. all pests improve crop productivity
ⓓ. predators feed on pests; parasites use them as hosts
Correct Answer: predators feed on pests; parasites use them as hosts
Explanation: In an ecological community, pests may also function as prey or hosts for beneficial organisms. If the pest population is completely eliminated, predators that feed on it or parasites that require it as a host may also decline. This can disrupt natural regulatory relationships within the field ecosystem. Biological control therefore often aims for population management rather than total eradication, keeping the pest below economically damaging levels while preserving important ecological interactions.
107. Before introducing a biological-control agent into a field, an agricultural scientist studies the target pest's life cycle, feeding behaviour, habitat and natural enemies. Why is this information useful?
ⓐ. It guarantees complete elimination of every non-crop organism
ⓑ. It proves that chemical pesticides are always necessary
ⓒ. It allows the scientist to choose a control strategy that matches the ecology of the pest
ⓓ. It prevents the scientist from choosing a control strategy suited to the pest's ecology
Correct Answer: It allows the scientist to choose a control strategy that matches the ecology of the pest
Explanation: Effective biological control depends on understanding the biology and ecology of both the pest and its natural enemies. Information about life cycle, feeding pattern and habitat can reveal when and where the pest is most vulnerable and which predator, parasite or microbial agent is most appropriate. This ecological knowledge makes control more targeted and reduces the chance of using an unsuitable method. Biocontrol is therefore based on informed manipulation of biological relationships rather than simple replacement of one pesticide with another.
108. Consider the predator-target relationships shown below.
| Predator | Target organism |
|---|
| I. Ladybird beetle | Aphids |
| II. Dragonfly | Mosquitoes |
Which evaluation is correct?
ⓐ. Only I is correct
ⓑ. Only II is correct
ⓒ. Both I and II are correct
ⓓ. Neither I nor II is correct
Correct Answer: Both I and II are correct
Explanation: Both predator-target relationships are standard examples of biological control. Ladybird beetles feed on aphids and can help reduce aphid populations on plants, while dragonflies prey on mosquitoes. These examples demonstrate how naturally occurring predators can be useful in controlling pest populations without depending exclusively on chemical insecticides. The biological value comes from exploiting predator-prey relationships already present in the ecosystem.
109. A crop field is heavily infested with aphids. Which biological-control organism would be most directly useful?
ⓐ. Ladybird beetle
ⓑ. Methanobacterium
ⓒ. Saccharomyces cerevisiae
ⓓ. Rhizobium
Correct Answer: Ladybird beetle
Explanation: Ladybird beetles are natural predators of aphids and are therefore useful biological-control agents in aphid-infested fields. Their feeding activity directly reduces the number of aphids attacking plants. This example is important because it illustrates biological control through predation rather than through microbial toxins or chemical pesticides. The mechanism is ecological: the predator consumes the pest and helps keep its population at a manageable level.
110. Bacillus thuringiensis is useful in biological pest management primarily because it can control
ⓐ. aphids by nitrogen fixation
ⓑ. butterfly caterpillars via Bt toxin action
ⓒ. fungal root diseases by phosphorus absorption
ⓓ. mosquitoes through predatory feeding
Correct Answer: butterfly caterpillars via Bt toxin action
Explanation: Bacillus thuringiensis, commonly abbreviated as Bt, is a bacterial biological-control agent used against butterfly caterpillars. Unlike predator-based control, Bt acts through a microbial product that affects susceptible insect larvae after they ingest the biological preparation. This example demonstrates that biocontrol can involve microorganisms as well as predators. The key biological relationship is Bt bacterium -> susceptible caterpillar larvae -> pest control.
111. A Bt formulation is being prepared for application to plants vulnerable to caterpillar attack. The usual field method involves
ⓐ. dissolving purified methane in irrigation water
ⓑ. applying activated sewage sludge to the leaves
ⓒ. introducing living caterpillars into the soil
ⓓ. mixing dried spores with water and spraying plants
Correct Answer: mixing dried spores with water and spraying plants
Explanation: Bacillus thuringiensis can be used as a biological pesticide in the form of dried spores. These spores are mixed with water and sprayed onto plants that are vulnerable to caterpillar attack. The biological agent is therefore placed directly where feeding larvae are likely to encounter it. The effectiveness of this method depends on the insect larvae ingesting the material while feeding on the treated plant.
112. A caterpillar feeds on leaves that were previously sprayed with a Bacillus thuringiensis preparation. Which sequence best describes the biological-control process?
ⓐ. The bacterial spores fertilise the leaf -> the plant stops producing food -> the caterpillar dies
ⓑ. The larva inhales the preparation -> nitrogen fixation begins -> the caterpillar becomes harmless
ⓒ. The larva ingests the bacterial preparation -> toxin action occurs in the larval gut -> the caterpillar dies
ⓓ. The larva ingests the bacterial preparation -> spores remain inactive in the gut -> external damage to the leaf kills the caterpillar
Correct Answer: The larva ingests the bacterial preparation -> toxin action occurs in the larval gut -> the caterpillar dies
Explanation: Bt control depends on ingestion by the susceptible insect larva. The caterpillar consumes plant material carrying the bacterial preparation, after which toxin action occurs within the larval gut and ultimately kills the caterpillar. This is an important mechanism-based distinction because merely spraying the organism is not the complete explanation; the target larva must consume it. The sequence connects application, ingestion and biological effect into one continuous process.
113. A field treated with Bacillus thuringiensis shows a marked decline in caterpillar damage, while many other insects remain unaffected. This result most strongly supports the conclusion that
ⓐ. Bt can eliminate susceptible caterpillars only by causing equally severe mortality among many non-target insects in the field
ⓑ. Bt can provide targeted control of susceptible caterpillars without necessarily harming all insects
ⓒ. Bt increases the growth of every insect in the field
ⓓ. Bt functions mainly as a soil fertiliser
Correct Answer: Bt can provide targeted control of susceptible caterpillars without necessarily harming all insects
Explanation: The described result is consistent with the target-specific biological-control role of Bacillus thuringiensis. Susceptible caterpillars ingest the bacterial preparation and are killed by toxin action, while other insects may remain unharmed. This selectivity is one reason biological agents can be environmentally preferable to broad-spectrum chemical pesticides. The observation demonstrates that successful pest control does not require destruction of the entire insect community.
114. Bacillus thuringiensis is also connected with crop biotechnology. Which statement correctly represents this connection?
ⓐ. Bt toxin genes can be introduced into plants, and Bt cotton is an example
ⓑ. Bt is used only as a free-living nitrogen-fixing bacterium in cotton fields
ⓒ. Bt cotton is produced by coating cotton seeds with sewage sludge
ⓓ. Bt genes are introduced into insects so that they produce fertiliser
Correct Answer: Bt toxin genes can be introduced into plants, and Bt cotton is an example
Explanation: Bt biological control also connects with crop biotechnology because genes responsible for Bt toxin can be introduced into plants. Bt cotton is a familiar example of this approach. A plant carrying the relevant Bt toxin gene can produce the insecticidal factor and thereby gain protection against susceptible pests. This links a microbial pest-control mechanism with a crop-based form of biological protection.
115. Trichoderma used in biological control is best described as
ⓐ. a free-living fungus associated with root ecosystems
ⓑ. a nitrogen-fixing bacterium restricted to legume nodules
ⓒ. an insect virus that infects only vertebrates
ⓓ. a methanogen found mainly in cattle rumen
Correct Answer: a free-living fungus associated with root ecosystems
Explanation: Trichoderma species are free-living fungi that are commonly associated with root ecosystems. They are important in biological control because they can act against several plant pathogens. This makes them different from Bt, which is a bacterium used mainly against caterpillar pests, and from baculoviruses, which are viral agents targeting insects and other arthropods. Correct classification of the organism is important for understanding the diversity of biological-control agents.
116. A farmer wants to use a microbial agent to suppress several plant pathogens in the root environment. Which biological-control organism is most appropriate?
ⓐ. Acetobacter aceti
ⓑ. Methanobacterium
ⓒ. Monascus purpureus
ⓓ. Trichoderma fungus
Correct Answer: Trichoderma fungus
Explanation: Trichoderma is a free-living fungus associated with root ecosystems and is used in the biological control of several plant pathogens. Its importance lies in disease suppression rather than insect predation, methane production or industrial acid synthesis. This example shows that biocontrol includes management of plant diseases as well as insect pests. The organism-habitat-function relationship is therefore Trichoderma -> root ecosystem -> suppression of plant pathogens.
117. Baculoviruses used in biological control are primarily pathogens of
ⓐ. plants and fungi
ⓑ. insects and arthropods
ⓒ. cattle and other mammals
ⓓ. nitrogen-fixing bacteria
Correct Answer: insects and arthropods
Explanation: Baculoviruses are viral pathogens of insects and other arthropods. Their biological-control value comes from their ability to infect particular pest species while having a very limited effect on many non-target organisms. This makes them especially useful where selective pest suppression is desirable. They should not be confused with plant pathogens or vertebrate viruses, because their target range is specifically associated with insects and related arthropods.
118. The majority of baculoviruses used as biological-control agents belong to the genus
ⓐ. Propionibacterium
ⓑ. Lactobacillus
ⓒ. Trichoderma
ⓓ. Nucleopolyhedrovirus
Correct Answer: Nucleopolyhedrovirus
Explanation: Nucleopolyhedrovirus is the genus associated with the majority of baculoviruses used in biological control. These viruses infect specific insect or arthropod hosts and can therefore be used to suppress pest populations. The important point is not simply the viral name but the ecological role: baculoviruses are valuable because their host range can be highly restricted, allowing targeted pest management with comparatively little disturbance to non-target organisms.
119. A biological-control virus kills one particular insect pest species efficiently but has little or no effect on unrelated insects. Why can this narrow host range be an advantage?
ⓐ. It allows selective suppression of the pest while conserving many non-target organisms
ⓑ. It guarantees destruction of every organism in the agricultural ecosystem
ⓒ. It prevents selective suppression of the pest while conserving many non-target organisms
ⓓ. It eliminates the need to identify the pest species before treatment
Correct Answer: It allows selective suppression of the pest while conserving many non-target organisms
Explanation: A narrow host range means that the biological-control agent affects a limited group of organisms rather than indiscriminately attacking many species. For baculoviruses, this species-specific or narrow-spectrum action is environmentally valuable because beneficial insects and other non-target organisms can be conserved while the target pest is suppressed. In biological control, such specificity is often an advantage because effective pest management can be achieved without causing unnecessary ecological disruption.
120. A pest-management programme is being designed for an ecologically sensitive area containing beneficial insects, birds, fish and mammals. Why are suitably chosen baculoviruses especially attractive in this situation?
ⓐ. They are broad-spectrum chemicals that kill most organisms rapidly
ⓑ. They cannot be highly host-specific and generally spare plants, vertebrates and many non-target insects
ⓒ. They improve soil fertility by fixing atmospheric nitrogen
ⓓ. They can be highly host-specific and generally spare plants, vertebrates and many non-target insects
Correct Answer: They can be highly host-specific and generally spare plants, vertebrates and many non-target insects
Explanation: Baculoviruses are particularly valuable in integrated pest management because many have a narrow and highly specific host range. They do not have negative effects on plants, mammals, birds, fish or many non-target insects. This selectivity makes them suitable for ecologically sensitive areas where preservation of beneficial organisms is important. Their usefulness therefore comes from combining effective pest suppression with minimal disturbance of the surrounding biological community.
