Question 1

Bioleaching microbes — organisms that solubilize metals and can accumulate silver  Which microorganism group is classically used to leach metals from sulfide ores and is well known in biohydrometallurgy (including processes that can lead to silver a…

Accepted Answer

Introduction / Context: Bioleaching harnesses chemolithoautotrophic bacteria to oxidize sulfide minerals, releasing metals into solution. These processes operate at scale for copper, gold, and other metals, and can lead to mobilization and recovery of precious metals such as silver. Given Data / Assumptions: Thiobacillus (now reclassified largely as Acidithiobacillus) oxidizes ferrous iron and reduced sulfur compounds. Their metabolism generates ferric iron and sulfuric acid, which attack metal sulfides. Other listed microbes are not the classical bioleaching workhorses. Concept / Approach: Acidithiobacillus ferrooxidans and related species catalyze oxidative dissolution of ores such as chalcopyrite and argentiferous minerals. The resulting metal-rich liquors can be processed to recover copper, gold, silver, and other metals. Step-by-Step Solution: Associate bioleaching with sulfur and iron oxidizers under acidic conditions.Recall Thiobacillus/Acidithiobacillus as canonical bioleaching bacteria.Exclude heterotrophs (Pseudomonas spp.) and floc-forming wastewater bacteria (Zoogloea).Select Thiobacillus (Acidithiobacillus) as correct. Verification / Alternative check: Industrial heap/dump bioleaching operations cite Acidithiobacillus spp. as primary catalysts, corroborating their central role in metal solubilization and recovery. Why Other Options Are Wrong: Pseudomonads are versatile bioremediators but not primary ore-leaching bacteria. Zoogloea ramigera is associated with activated sludge flocs. Yeast is not used for sulfide ore bioleaching. Common Pitfalls: Conflating general bioremediation microbes with acidophilic lithotrophs specialized for ore oxidation. Final Answer: Thiobacillus (e.g., Acidithiobacillus spp.)

Question 2

Baculoviridae subgroups — Which of the following are recognized subgroups within baculoviruses used in insect pathology and biocontrol?

Accepted Answer

Introduction / Context: Baculoviridae is a family of large, double-stranded DNA viruses that infect insects, especially Lepidoptera. In applied microbiology and biocontrol, students frequently encounter the two principal subgroups used for field and lab work. Recognizing these subgroups helps in selecting appropriate viral agents for pest management and in interpreting literature on viral bioinsecticides. Given Data / Assumptions: Baculoviruses are classified into distinct groups based on occlusion body morphology and genome traits. NPVs and GVs are the classic, widely cited subgroups within Baculoviridae. Some insect viruses used in control (for example Oryctes rhinoceros nudivirus) belong to other families (Nudiviridae), not Baculoviridae. Concept / Approach: The key distinction historically is that Nuclear Polyhedrosis Viruses (NPVs) form polyhedral occlusion bodies containing multiple virions, whereas Granulosis Viruses (GVs) form granular occlusion bodies typically with a single virion. Both are true baculoviruses and have been developed as bioinsecticides. Viruses of the Oryctes type are nudiviruses and therefore do not belong to Baculoviridae. Step-by-Step Solution: Identify which listed items are members of Baculoviridae.NPVs: yes — a major subgroup applied in biocontrol.GVs: yes — another major subgroup used in orchard and field settings.Oryctes-type viruses: nudiviruses, not baculoviruses.Therefore, the correct combined choice is both NPVs and GVs. Verification / Alternative check: Standard virology references and pest-management manuals consistently group NPVs and GVs under Baculoviridae, while nudiviruses are placed separately. Why Other Options Are Wrong: NPVs alone or GVs alone are incomplete answers. Oryctes-type nudiviruses are not baculoviruses. None of these: incorrect, because NPVs and GVs are baculoviruses. Common Pitfalls: Confusing “occlusion body viruses” broadly and assuming all insect DNA viruses are baculoviruses; taxonomy distinguishes nudiviruses from baculoviruses. Final Answer: Both (a) and (b)

Question 3

Bioremediation strategy — Under toxic pollutant stress, when is degradation performance and microbial resistance typically better: mixed cultures or single isolates?

Accepted Answer

Introduction / Context: Environmental biotechnology often leverages microbial communities to degrade toxic pollutants in soil and wastewater. Choosing between a mixed consortia and a single pure culture affects resilience, pathway completeness, and resistance to inhibitory compounds. Given Data / Assumptions: Toxic pollutants can inhibit or kill sensitive strains. Complex contaminants may require multi-step pathways distributed across different microbes. Cometabolism and cross-feeding commonly occur in mixed communities. Concept / Approach: Mixed microbial populations typically show higher functional redundancy, broader catabolic gene pools, and synergistic interactions. These features enhance both the rate of degradation and resistance to toxic shocks. Adding heavy metals usually increases toxicity and lowers performance unless carefully controlled chelation is used, so “with metals” is not an advantage here. Step-by-Step Solution: Compare the catabolic breadth of mixed consortia versus single isolates.Assess resilience: mixed communities buffer shocks due to redundancy.Conclude that mixed cultures outperform single isolates for pollutant degradation under toxic conditions. Verification / Alternative check: Activated sludge and biofilm systems routinely outperform single-strain reactors for diverse industrial effluents, demonstrating the practical benefit of consortia. Why Other Options Are Wrong: Single isolate: limited pathway range and lower resilience. Adding metals: generally increases toxicity; not a valid enhancement strategy. “Neither” contradicts extensive process engineering evidence. Common Pitfalls: Assuming a “superbug” can handle all pollutants; in practice, stable consortia deliver better, more reliable performance. Final Answer: Mixed cell population is used

Question 4

Wastewater denitrification — Which options are used to reduce nitrate (NO3−) in wastewater treatment applications?

Accepted Answer

Introduction / Context: Denitrification removes nitrate by reducing it to gaseous nitrogen species, a key step in preventing eutrophication. Process engineers exploit heterotrophic denitrifiers and tailored reactor designs to achieve stable nitrate removal in industrial and municipal wastewaters. Given Data / Assumptions: Heterotrophic denitrifiers require an electron donor (e.g., methanol) under anoxic conditions. Immobilized or encapsulated cells can improve stability and retention in reactors. Nitrifiers such as Nitrosomonas perform oxidation (nitrification), not nitrate reduction. Concept / Approach: Hypomicrobium species grow with methanol and can reduce nitrate in anoxic conditions. Micrococcus denitrificans has been used in immobilized systems (e.g., liquid membranes) to enhance nitrate removal and protect cells from washout or toxic shocks. Nitrosomonas europaea oxidizes ammonia to nitrite and is not a denitrifier. Step-by-Step Solution: Identify processes that reduce nitrate (denitrification) rather than oxidize ammonia.Select Hypomicrobium + methanol and immobilized Micrococcus denitrificans as valid denitrification strategies.Exclude nitrifiers like Nitrosomonas which perform nitrification, not denitrification. Verification / Alternative check: Standard design manuals specify methanol-fed denitrification and note benefits of immobilized biocatalysts for steady performance and low sludge yield. Why Other Options Are Wrong: Nitrosomonas europaea: oxidizes NH3 to NO2−; does not reduce nitrate. Aeromonas strictly aerobic only: denitrification requires anoxic conditions and specific organisms capable of nitrate respiration. Common Pitfalls: Confusing the two-step nitrogen removal train: nitrification (aerobic) followed by denitrification (anoxic/anaerobic) with different microbial guilds. Final Answer: Both (a) and (b)

Question 5

Industrial wastewater microbiology — Which organism is classically associated with forming dense flocs and accumulating in factory or industrial wastes during activated-sludge treatment?

Accepted Answer

Introduction / Context: Activated-sludge systems rely on microbial flocs that settle efficiently. Certain bacteria produce extracellular polymeric substances (EPS) that bind cells and particles into compact masses. Recognizing key floc-formers helps diagnose bulking, poor settling, and process stability issues in industrial effluent treatment. Given Data / Assumptions: Industrial effluents often contain organics that foster EPS production. Good floc formation aids secondary clarification and effluent quality. Not all heterotrophs are primary floc-formers. Concept / Approach: Zoogloea ramigera is a classic floc-forming bacterium producing abundant EPS (zoogloeal matrix), common in activated-sludge and certain factory waste streams. While species like Pseudomonas degrade diverse organics, they are not the prototypical floc formers referenced in foundational wastewater microbiology texts. Step-by-Step Solution: Identify organisms linked to EPS-rich flocs: Zoogloea spp.Exclude sulfur oxidizers (Thiobacillus) relevant to acid mine drainage, not general floc formation.Recognize Z. ramigera as the canonical floc-forming bacterium in industrial and municipal systems. Verification / Alternative check: Microscopic examination of healthy sludge often reveals branched zoogloeal structures; process guides cite Z. ramigera for stable floc formation. Why Other Options Are Wrong: P. aeruginosa and P. putida: versatile degraders but not the classic floc archetype. Thiobacillus (Acidithiobacillus): sulfur oxidizers in acidic environments. V. cholerae: human pathogen, not associated with activated-sludge flocs. Common Pitfalls: Equating high COD removal strictly with floc formation; degraders and floc-formers can be distinct guilds in the biomass. Final Answer: Zoogloea ramigera

Question 6

Antibiotic biocontrol — Streptomyces griseochromogenes is reported to show a potent curative effect against which plant disease?

Accepted Answer

Introduction / Context: Members of the genus Streptomyces produce many agriculturally important antibiotics. Streptomyces griseochromogenes is historically linked with an antibiotic effective against the rice blast fungus, a major pathogen of rice worldwide. Given Data / Assumptions: Rice blast (caused by Pyricularia/Magnaporthe oryzae) threatens yield and requires integrated control. Antibiotics from Streptomyces have been explored for plant disease management. Blasticidin S is a well-known product associated with S. griseochromogenes. Concept / Approach: Blasticidin S exhibits strong activity against rice blast, making S. griseochromogenes notable in the history of plant disease control. Recognizing pathogen–antibiotic pairings is useful in agribiotech and plant pathology exams. Step-by-Step Solution: Identify the antibiotic producer: S. griseochromogenes.Recall its primary agricultural application: control of rice blast.Select rice blast as the correct associated disease. Verification / Alternative check: Historical literature reports blasticidin S from S. griseochromogenes with efficacy against rice blast in paddy systems. Why Other Options Are Wrong: Yellow blight of maize, soybean milo disease, and eye spot of sugarcane have different etiologies and control measures not centered on blasticidin S from this species. Common Pitfalls: Confusing producers of polyoxins or kasugamycin with blasticidin S; multiple Streptomyces species yield distinct antifungals. Final Answer: Rice blast disease (Pyricularia oryzae/Magnaporthe oryzae)

Question 7

Phenol removal from complex wastewaters — Which biocatalyst strategies are documented for degrading phenols in hospital, laboratory, and coal-to-coke processing effluents?

Accepted Answer

Introduction / Context: Phenolic compounds are toxic and persistent in many industrial and clinical effluents. Biocatalytic approaches using fungi and bacteria can achieve effective phenol degradation when configured as immobilized or adsorbed systems to withstand toxicity and hydraulic shear. Given Data / Assumptions: Immobilization enhances stability and reusability of biocatalysts. Aureobasidium pullulans and Pseudomonas spp. are reported phenol degraders under appropriate conditions. Support matrices (asbestos historically; anthracite coal; alginate) have been used to retain biomass. Concept / Approach: Both fungal and bacterial routes can mineralize phenol. Adsorbed or entrapped cells experience reduced washout and may tolerate inhibitory spikes better. The question cites specific historical configurations that have been described in the literature for phenol-laden effluents from hospitals, labs, and coking operations. Step-by-Step Solution: Evaluate each listed immobilized system for plausibility and precedent.A. pullulans on fibrous supports: reported for phenolic waste polishing.Pseudomonas spp. on anthracite or in alginate: widely used for phenol degradation.Therefore, both (a) and (b) are acceptable, documented strategies. Verification / Alternative check: Papers and process notes in environmental biotech describe immobilized Pseudomonas and selected fungi for phenol removal, often achieving higher tolerance and kinetics than freely suspended cells. Why Other Options Are Wrong: Phanerochaete chrysosporium is a strong lignin degrader and can attack phenolics, but the option claims exclusivity regardless of conditions, which is inaccurate versus the documented systems. Abiotic UV alone is unreliable for complete mineralization of phenols in these complex matrices. Common Pitfalls: Assuming a single “best” organism; in practice, matrix choice, loading rates, and toxicity dictate which immobilized system performs best. Final Answer: Both (a) and (b)

Question 8

Fungal disease control — Which polyoxin variant is reported as most effective against the rice sheath blight pathogen Pellicularia sasakii (Rhizoctonia solani)?

Accepted Answer

Introduction / Context: Polyoxins are nucleoside-peptide antibiotics produced by Streptomyces species that inhibit chitin synthase, thereby suppressing fungal growth. Rice sheath blight, caused by Pellicularia sasakii (syn. Rhizoctonia solani), is a major disease where specific polyoxin variants show differing efficacy. Given Data / Assumptions: Polyoxin variants (B, C, D, L) differ in structure and potency. Target pathogen is a basidiomycete forming sclerotia and infecting sheaths. Mode of action is inhibition of chitin biosynthesis in fungal cell walls. Concept / Approach: Among the polyoxins, Polyoxin D has been cited as particularly effective against R. solani. Efficacy relates to uptake, stability, and binding to the chitin synthase target complex, leading to impaired cell wall synthesis and pathogen suppression. Step-by-Step Solution: List polyoxin variants and their reported activities.Match variant with pathogen sensitivity (sheath blight agent).Select Polyoxin D as the most effective against the stated pathogen. Verification / Alternative check: Plant pathology references and historical trials document Polyoxin D’s superior activity on Rhizoctonia spp. compared to several other variants. Why Other Options Are Wrong: B, C, L: active but generally less effective against this target organism. Kasugamycin is an aminoglycoside primarily used against blast; it is not a polyoxin and has a different target (protein synthesis). Common Pitfalls: Conflating rice blast (kasugamycin-responsive) with sheath blight (polyoxin-responsive); they involve different pathogens and antibiotic classes. Final Answer: Polyoxin D

Question 9

Color removal from pulp and paper mill effluents — Which biological options are documented to decolorize such effluents?

Accepted Answer

Introduction / Context: Pulp and paper mill effluents contain lignin-derived chromophores and recalcitrant organics. White-rot fungi produce extracellular oxidative enzymes (laccases, manganese peroxidase, lignin peroxidase) capable of decolorizing and transforming these compounds. Given Data / Assumptions: Enzyme-mediated oxidation is key for color removal. Immobilization (e.g., alginate entrapment) can stabilize fungal biocatalysts. Nitrifiers do not target lignin chromophores. Concept / Approach: Trametes versicolor (syn. Coriolus versicolor) and Phanerochaete chrysosporium are model organisms for lignin degradation and effluent decolorization. Both free and immobilized forms have been reported to reduce color and COD in pulp mill wastewaters by attacking aromatic structures. Step-by-Step Solution: Identify organisms with strong ligninolytic enzyme systems.Confirm feasibility of immobilization (e.g., alginate beads) for reactor use.Select both listed fungal options as valid decolorization strategies. Verification / Alternative check: Numerous studies demonstrate color reduction using these fungi in batch and continuous setups, with enzyme assays correlating activity to decolorization metrics. Why Other Options Are Wrong: Nitrosomonas europaea: oxidizes ammonia; unrelated to chromophore breakdown. Physical sedimentation alone does not remove dissolved color-causing organics. Common Pitfalls: Expecting standard activated sludge to remove color efficiently; specialized oxidative systems are often needed for lignin-derived compounds. Final Answer: Both (a) and (b)

Question 10

Algae control via nitrogen removal — Which organism has been used to oxidize ammonia and thereby help prevent algal growth in water systems?

Accepted Answer

Introduction / Context: Algal blooms in aquatic systems are often fueled by available nitrogen (and phosphorus). Biological nitrification can convert ammonia, a form readily assimilated by algae, into nitrate, which can be further removed by denitrification or reduced in bioavailability, helping control algal growth. Given Data / Assumptions: Ammonia-oxidizing bacteria (AOB) convert NH3/NH4+ to nitrite (NO2−). Nitrite-oxidizing bacteria (NOB) convert NO2− to NO3−. Denitrifiers reduce nitrate to gaseous nitrogen under anoxic conditions. Concept / Approach: Nitrosomonas europaea is a model AOB used in biofilters and nitrification reactors. By oxidizing ammonia, it reduces the pool of algal-available nitrogen in the form most stimulatory for growth, forming part of an integrated nutrient management strategy in water treatment. Step-by-Step Solution: Identify the target transformation: NH3 to NO2− (nitrification step 1).Select the canonical AOB: Nitrosomonas europaea.Recognize that other listed organisms are denitrifiers, not ammonia oxidizers. Verification / Alternative check: Engineering texts on aquaculture and drinking water biofiltration cite Nitrosomonas-based biofilters for ammonia control and consequent algae suppression. Why Other Options Are Wrong: Hypomicrobium and Micrococcus denitrificans: employed for denitrification, not ammonia oxidation. Anabaena (cyanobacteria): fixes nitrogen and can contribute to blooms rather than prevent them. Common Pitfalls: Confusing nitrification (aerobic) with denitrification (anoxic); each step involves different organisms and goals in nutrient control. Final Answer: Nitrosomonas europaea (ammonia-oxidizing bacterium)

Question 11

Biomining / Bioleaching — Which bacteria are considered in biological leaching of sulfide ores and related operations?

Accepted Answer

Introduction / Context: Bioleaching exploits chemolithotrophic bacteria that oxidize reduced sulfur and ferrous iron in sulfide minerals, facilitating metal solubilization. The best-known genera historically include Thiobacillus (now Acidithiobacillus) and related iron-oxidizing bacteria used in heaps, dumps, and stirred bioreactors. Given Data / Assumptions: Target metals are often associated with sulfide minerals (e.g., chalcopyrite, pyrite). Bacteria catalyze oxidation of Fe2+ to Fe3+ and reduced sulfur to sulfate, generating ferric iron and acid that attack the ore. Nomenclature has changed over time; older and newer names can refer to the same functional organisms. Concept / Approach: Acidithiobacillus thiooxidans (formerly T. thiooxidans) oxidizes reduced sulfur; Acidithiobacillus ferrooxidans (formerly T. ferrooxidans) oxidizes Fe2+ and sulfur; and the historical designation Ferrobacillus ferrooxidans overlaps with iron-oxidizing bacteria considered in early bioleaching studies. All are part of the microbial consortium relevant to biomining. Step-by-Step Solution: Match each listed bacterium to bioleaching roles (sulfur/iron oxidation).Recognize synonymy and historical naming conventions.Conclude that all listed bacteria are considered in bioleaching contexts. Verification / Alternative check: Biomining case studies (e.g., copper heap leaching) repeatedly identify A. ferrooxidans and A. thiooxidans as dominant catalysts. Why Other Options Are Wrong: E. coli K-12: a laboratory heterotroph with no role in sulfide bioleaching. Common Pitfalls: Assuming name changes mean different organisms; taxonomy updates often rename well-known biomining species. Final Answer: All of these

Question 12

Agrochemicals and biocontrol — Milbemycin (a macrocyclic lactone related to avermectins) is known to exhibit a broad spectrum of activity primarily against which agricultural targets?

Accepted Answer

Introduction / Context: Milbemycins are macrocyclic lactone metabolites produced by Streptomyces species. In crop protection and veterinary settings, they are valued for potent activity against a wide range of invertebrate agricultural pests, especially plant-parasitic nematodes, phytophagous mites, and several insect orders. This question checks recognition of the correct target spectrum and avoids distractors that would misclassify milbemycin as an herbicide or a narrow-use compound. Given Data / Assumptions: Milbemycin targets invertebrate nervous systems by enhancing inhibitory neurotransmission. Field uses include mitigation of mites on ornamentals/vegetables and suppression of nematodes. Herbs (culinary or crop herbs) are plants, not a pest class; “all of these” would incorrectly include them. Concept / Approach: Mode of action involves opening glutamate-gated chloride channels in invertebrates, leading to paralysis. Because many pest mites and nematodes share this physiological vulnerability, milbemycin has a broad “pesticide” spectrum within invertebrates. It is not a herbicide and does not target plants. Step-by-Step Solution: Identify what milbemycin chemically is (macrocyclic lactone) and its known targets (mites, nematodes, some insects).Exclude “herbs” because they are plants, not pest targets.Exclude “insects only” because activity also covers mites and nematodes.Exclude “all of these” since it would wrongly include herbs. Verification / Alternative check: Labels and extension bulletins consistently list activity against Tetranychid mites and certain nematodes; no reputable source lists milbemycin as a plant-killing herbicide. Why Other Options Are Wrong: b) “Agricultural herbs” mislabels plants as targets; incorrect.c) Too narrow; ignores acaricidal/nematicidal spectrum.d) Incorrectly includes herbs.e) Beneficial fungi are not primary targets; misclassification. Common Pitfalls: Confusing “broad spectrum” with “all living things”; spectrum refers to classes of pests, not crops. Final Answer: Agricultural pests (notably mites, nematodes, and certain insect pests).

Question 13

Aquatic ecology — The heavily polluted, highly organic waste–rich zone of a water body is properly termed which saprobic zone?

Accepted Answer

Introduction / Context: The saprobic system classifies stretches of rivers and reservoirs according to organic pollution load and biological indicators. Correct terminology distinguishes heavily polluted reaches from moderately and slightly polluted waters. This is essential for biomonitoring, wastewater impact assessment, and ecological restoration planning. Given Data / Assumptions: “Heavily polluted” implies high biochemical oxygen demand and low dissolved oxygen. Indicator taxa shift from sensitive to tolerant species as pollution increases. Saprobic zones progress from polysaprobic → mesosaprobic → oligosaprobic as water quality improves downstream. Concept / Approach: Polysaprobic waters contain abundant easily degradable organic matter. Microbial respiration is intense, causing hypoxia and favoring tolerant organisms. Mesosaprobic zones indicate moderate loads with partial recovery. Oligosaprobic denotes slight pollution or near-clean conditions with higher oxygen and sensitive biota. Step-by-Step Solution: Map “heavily polluted” to saprobic classification → polysaprobic.Recognize mesosaprobic as moderate and oligosaprobic as slight pollution.Exclude terms unrelated to saprobity (e.g., salinity-based zones). Verification / Alternative check: Classic limnology texts and bioindicator protocols use these exact zone names and associate taxa to each class. Why Other Options Are Wrong: b) Mesosaprobic is moderate, not heavy.c) Oligosaprobic is slight pollution/clean water.d) Xenosaprobic refers to very clean conditions; opposite of heavy pollution.e) Eusaline concerns salinity, not organic pollution. Common Pitfalls: Confusing similar-sounding terms (polysaprobic vs mesosaprobic) or mixing saprobity with other water quality classifications like salinity or trophic state. Final Answer: Polysaprobic zone (heavily polluted, low dissolved oxygen).

Question 14

Biocontrol of Colorado potato beetle — Which entomopathogenic fungus is widely documented to infect and suppress Leptinotarsa decemlineata in the field?

Accepted Answer

Introduction / Context: The Colorado potato beetle (Leptinotarsa decemlineata) is a notorious defoliator of potato and other Solanaceae. Biological control using entomopathogenic fungi offers a sustainable complement to chemical insecticides and helps manage resistance. Recognizing the best-studied fungal agents improves integrated pest management decisions. Given Data / Assumptions: Target pest: Colorado potato beetle (coleopteran). Common entomopathogenic fungi: Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii (Lecanicillium), Nomuraea rileyi (now Metarhizium rileyi). Host ranges vary; some fungi specialize in hemipterans or lepidopterans. Concept / Approach: Beauveria bassiana is broadly effective against many beetles, including the Colorado potato beetle, with commercial formulations registered in several regions. While Metarhizium anisopliae also targets certain beetles, B. bassiana has the strongest association and literature base for CPB suppression, especially under temperate field conditions. Step-by-Step Solution: Identify the pest as a beetle species → evaluate which fungi target coleopterans.Beauveria bassiana has extensive CPB efficacy data and product use.Select B. bassiana as the best-documented control agent. Verification / Alternative check: Extension guides and peer-reviewed trials report significant CPB mortality with B. bassiana sprays under conducive humidity and temperature. Why Other Options Are Wrong: b) Metarhizium anisopliae has coleopteran activity but is not the most classically cited CPB agent.c) Verticillium lecanii is more noted for aphids/whiteflies.d) Nomuraea rileyi targets lepidopteran larvae (e.g., Spodoptera).e) Isaria fumosorosea targets whiteflies/aphids; less prominent for CPB. Common Pitfalls: Overlooking environmental requirements: high humidity aids infection; UV and heat reduce spore viability, affecting field performance. Final Answer: Beauveria bassiana.

Question 15

Biological control strategies — Inundation (inundative release) involves what deployment pattern of natural enemies against a pest population?

Accepted Answer

Introduction / Context: Biological control uses beneficial organisms to reduce pest populations. Three classic strategies are importation (classical control), augmentation (including inundation and inoculation), and conservation. Understanding the difference between inundation and inoculation helps practitioners choose proper release rates and timing. Given Data / Assumptions: Pest outbreak requires rapid suppression. Natural enemies can be mass-reared and released. Short-term impact is prioritized over long-term establishment. Concept / Approach: Inundation is an augmentation tactic that floods the cropping system with high densities of biocontrol agents for immediate impact, analogous to a biological “pesticide.” It differs from inoculation, which releases small numbers early for gradual build-up, and from classical control, which seeks long-term establishment of introduced natural enemies. Step-by-Step Solution: Define inundation → many agents, short time frame.Align with goal → quick knockdown of pest population.Choose option describing high, short-term releases. Verification / Alternative check: Commercial releases of Trichogramma wasps or entomopathogenic nematodes during peak pest windows exemplify inundation. Why Other Options Are Wrong: b,d) Single-organism releases are not representative.c) Long-term continuous releases describe different management or repeated inoculative strategies.e) Not a biocontrol method. Common Pitfalls: Expecting establishment from inundation; success is measured by immediate suppression, not persistence. Final Answer: Releasing a large number of organisms over a short time to suppress or destroy a target population.

Question 16

Microbial herbicides — Which of the following antibiotic-like herbicides is reported to be selectively effective against dicot (broadleaf) weeds?

Accepted Answer

Introduction / Context: Several microbial metabolites exhibit herbicidal properties and have been explored as “bioherbicides.” Understanding selectivity—whether a material targets dicots versus monocots—is essential for crop safety and weed spectrum management, especially in integrated weed control programs. Given Data / Assumptions: Herbicidins are nucleoside antibiotics from Streptomyces with herbicidal activity, notably toward dicots. Bialaphos is a tripeptide pro-herbicide that releases glufosinate; it is broadly non-selective. Cycloheximide and anisomycin are protein synthesis inhibitors, primarily referenced as antifungal or experimental tools, not selective field herbicides against dicots. Concept / Approach: Selectivity hinges on metabolic targets and plant physiology. Herbicidin A/B disrupt specific biochemical pathways that dicot weeds are more sensitive to, allowing selectivity under labeled uses. In contrast, glufosinate (from bialaphos) is non-selective and widely injures both monocots and dicots unless crop-tolerant traits are present. Step-by-Step Solution: Identify which compound pair has documented dicot selectivity → Herbicidin A/B.Exclude non-selective or non-field herbicides → bialaphos, glyphosate, cycloheximide, anisomycin.Confirm choice based on reported weed spectra. Verification / Alternative check: Research reports and screening studies highlight activity of herbicidin analogs against broadleaf weeds with reduced injury to certain monocots under specific conditions. Why Other Options Are Wrong: a,b) Not standard selective herbicides for dicot control in agronomy.d) Bialaphos/glufosinate are non-selective contact herbicides.e) Glyphosate is non-selective and systemic. Common Pitfalls: Assuming all microbially derived herbicides are selective; many act broadly and can harm crops without resistant traits. Final Answer: Herbicidin A and Herbicidin B.

Question 17

Weed spectrum — Which herbicide is reported as effective against perennial shrubs, annual weeds, and several problematic weeds of rice production systems?

Accepted Answer

Introduction / Context: Bialaphos is a microbial tripeptide that releases glufosinate (phosphinothricin) in planta, inhibiting glutamine synthetase and causing ammonia accumulation and plant death. It has been evaluated across cropping systems, including rice, for control of annual and perennial weeds and woody shrubs in non-crop situations. Given Data / Assumptions: Mode of action: glutamine synthetase inhibition leads to rapid chlorosis and necrosis. Spectrum: broad, covering many grasses and broadleaf weeds; not inherently selective without crop tolerance. Alternatives listed (cycloheximide, anisomycin, herbicidin) are not the standard broad-spectrum choice for rice weeds and shrubs. Concept / Approach: When a question points to efficacy against both perennial shrubs and annual weeds, a broad-spectrum non-selective herbicide fits best. Bialaphos/glufosinate is consistent with such a profile and has been studied in paddy systems and around rice culture, subject to registration and label constraints by country. Step-by-Step Solution: Match desired spectrum (annuals + perennials + shrubs) to known herbicides.Bialaphos (→ glufosinate) aligns with broad-spectrum control; choose it.Exclude narrow/selective or non-field agents. Verification / Alternative check: Field trials and literature show glufosinate efficacy across diverse weed flora; herbicidin is more dicot-selective and less used for grasses; cycloheximide/anisomycin are not standard field herbicides. Why Other Options Are Wrong: a,b) Protein synthesis inhibitors with limited herbicidal registrations.c) Dicot-leaning, not broadly effective on grasses or woody perennials.e) Auxin herbicides focus primarily on dicots; not the best fit for the stated broad spectrum including shrubs. Common Pitfalls: Assuming rice-system herbicides must be grass-selective; some are non-selective but used in specific management windows or non-crop areas. Final Answer: Bialaphos (pro-herbicide of glufosinate; broad-spectrum efficacy).

Environmental Protection Questions