Q.1 Which of the following is a primary source of organic carbon for heterotrophic microbes in soil?
Atmospheric CO₂
Root exudates
Nitrogen gas
Phosphate minerals
Explanation - Root exudates release sugars, amino acids and organic acids that serve as readily available carbon for heterotrophic microorganisms.
Correct answer is: Root exudates
Q.2 What is the main ecological role of nitrogen‑fixing bacteria such as Azotobacter in agricultural soils?
Decomposing lignin
Converting atmospheric N₂ to ammonia
Oxidizing sulfur compounds
Producing antibiotics
Explanation - Nitrogen‑fixers possess the enzyme nitrogenase that reduces N₂ to NH₃, making nitrogen available to plants.
Correct answer is: Converting atmospheric N₂ to ammonia
Q.3 In a bioremediation project, which microbial process is most effective for degrading petroleum hydrocarbons under aerobic conditions?
Methanogenesis
Nitrification
Oxidative catabolism
Denitrification
Explanation - Aerobic bacteria oxidize hydrocarbons using oxygen as the electron acceptor, breaking them down into CO₂ and water.
Correct answer is: Oxidative catabolism
Q.4 Which of the following is NOT a typical method for assessing microbial diversity in an environmental sample?
16S rRNA gene sequencing
Plate count technique
Gram staining
Metagenomic shotgun sequencing
Explanation - Gram staining classifies bacteria by cell‑wall structure but does not provide a comprehensive view of community diversity.
Correct answer is: Gram staining
Q.5 The term ‘biofilm’ refers to:
A free‑living planktonic bacterial culture
A community of microbes attached to a surface and embedded in extracellular polymeric substances
A fungal spore bank
A viral replication complex
Explanation - Biofilms consist of microorganisms embedded in a self‑produced matrix that adheres to surfaces.
Correct answer is: A community of microbes attached to a surface and embedded in extracellular polymeric substances
Q.6 Which electron acceptor is used by denitrifying bacteria during anaerobic respiration?
O₂
NO₃⁻
SO₄²⁻
Fe³⁺
Explanation - Denitrifiers reduce nitrate (NO₃⁻) to nitrogen gases (N₂, N₂O) under anaerobic conditions.
Correct answer is: NO₃⁻
Q.7 In the context of microbial ecology, ‘succession’ describes:
Genetic mutation rates in bacteria
The orderly change in species composition over time after a disturbance
The process of plasmid transfer
The movement of microbes in groundwater
Explanation - Ecological succession is the progressive replacement of microbial communities as conditions change.
Correct answer is: The orderly change in species composition over time after a disturbance
Q.8 Which of the following microorganisms is most commonly used in the bioremediation of heavy metals through biosorption?
Escherichia coli
Pseudomonas putida
Algae (e.g., Chlorella)
Bacillus subtilis
Explanation - Algal cell walls contain functional groups that bind heavy metals efficiently, making them good biosorbents.
Correct answer is: Algae (e.g., Chlorella)
Q.9 What is the primary advantage of using a mixed microbial consortium over a pure culture in wastewater treatment?
Simpler genetic manipulation
Broader range of metabolic capabilities
Easier isolation of individual strains
Reduced risk of pathogen emergence
Explanation - Consortia combine complementary metabolic pathways, allowing degradation of diverse pollutants.
Correct answer is: Broader range of metabolic capabilities
Q.10 Which of the following statements about archaea in soil ecosystems is correct?
They are primarily photosynthetic.
They are major contributors to methane oxidation.
They lack peptidoglycan in their cell walls.
They cannot survive in high‑temperature environments.
Explanation - Archaeal cell walls are composed of pseudo‑peptidoglycan or other polymers, not true peptidoglycan.
Correct answer is: They lack peptidoglycan in their cell walls.
Q.11 In a constructed wetland designed for nitrogen removal, which microbial process dominates the conversion of ammonia to nitrate?
Anammox
Nitrification
Denitrification
Methanogenesis
Explanation - Nitrifying bacteria oxidize NH₃ to NO₂⁻ and then to NO₃⁻ under aerobic conditions.
Correct answer is: Nitrification
Q.12 Which factor most strongly influences the rate of microbial decomposition of organic matter in soil?
Soil colour
Ambient light intensity
Temperature
Magnetic field strength
Explanation - Temperature affects enzyme activity; higher temperatures generally increase decomposition rates up to a limit.
Correct answer is: Temperature
Q.13 The term ‘phage therapy’ refers to:
Using bacteriophages to control bacterial pathogens
Applying fungal spores to enhance plant growth
Inoculating soils with nitrogen‑fixing bacteria
Employing viruses to degrade pollutants
Explanation - Phage therapy utilizes viruses that specifically infect and lyse bacterial cells as an alternative to antibiotics.
Correct answer is: Using bacteriophages to control bacterial pathogens
Q.14 Which of the following is a typical indicator of microbial water quality in a freshwater stream?
Dissolved oxygen concentration
Total suspended solids
Coliform bacteria count
pH level
Explanation - Coliforms, especially fecal coliforms, indicate potential contamination by pathogens.
Correct answer is: Coliform bacteria count
Q.15 In the context of microbial ecology, ‘functional redundancy’ means:
Multiple species performing the same ecological function
Redundant gene sequences within a single genome
Repeated cycles of the same metabolic pathway
Duplicated laboratory assays for the same parameter
Explanation - Functional redundancy provides ecosystem stability because loss of one species can be compensated by others.
Correct answer is: Multiple species performing the same ecological function
Q.16 Which of the following gases is a direct product of microbial methanogenesis?
Carbon dioxide
Methane
Nitrous oxide
Hydrogen sulfide
Explanation - Methanogenic archaea produce CH₄ as the final step in the decomposition of organic substrates under strict anaerobic conditions.
Correct answer is: Methane
Q.17 What is the primary purpose of a ‘bioaugmentation’ strategy in contaminated soils?
Adding nutrients to stimulate native microbes
Inoculating the site with specialized pollutant‑degrading microbes
Increasing soil pH to neutralize acidity
Introducing earthworms to improve aeration
Explanation - Bioaugmentation introduces exogenous microorganisms that possess the metabolic pathways needed for contaminant breakdown.
Correct answer is: Inoculating the site with specialized pollutant‑degrading microbes
Q.18 Which of the following is a common indicator organism for monitoring soil health in agricultural fields?
Streptomyces spp.
Thermus aquaticus
Vibrio cholerae
Clostridium difficile
Explanation - Streptomyces are abundant, involved in organic matter turnover, and their diversity reflects soil health.
Correct answer is: Streptomyces spp.
Q.19 In a microbial fuel cell (MFC), electrons generated by the oxidation of organic substrates are transferred to:
The cathode via an external circuit
The anode directly through the medium
The surrounding air
The microbial cell wall
Explanation - In MFCs, microbes oxidize substrate at the anode, releasing electrons that travel through an external circuit to the cathode, producing electricity.
Correct answer is: The cathode via an external circuit
Q.20 Which of the following is the most accurate description of ‘quorum sensing’ in bacteria?
Movement toward nutrients
Exchange of plasmids via conjugation
Regulation of gene expression in response to population density
Spore formation under stress
Explanation - Quorum sensing relies on the accumulation of signaling molecules to coordinate group behaviors once a threshold concentration is reached.
Correct answer is: Regulation of gene expression in response to population density
Q.21 Which microbial process is primarily responsible for the removal of nitrate from groundwater in denitrifying bioreactors?
Nitrification
Anammox
Denitrification
Ammonification
Explanation - Denitrifiers reduce nitrate (NO₃⁻) to nitrogen gases, thereby lowering nitrate concentrations.
Correct answer is: Denitrification
Q.22 Which of the following best describes a ‘keystone species’ in microbial ecology?
A species with the highest abundance
A species that has a disproportionate effect on ecosystem function relative to its abundance
A species that is a primary producer
A species that can survive extreme temperatures
Explanation - Keystone species shape community structure and ecosystem processes despite being numerically rare.
Correct answer is: A species that has a disproportionate effect on ecosystem function relative to its abundance
Q.23 In the nitrogen cycle, the conversion of ammonia to nitrite is carried out by:
Nitrobacter
Nitrosomonas
Anammox bacteria
Azotobacter
Explanation - Nitrosomonas oxidize NH₃ to NO₂⁻ during the first step of nitrification.
Correct answer is: Nitrosomonas
Q.24 Which analytical technique provides quantitative information on the functional genes present in an environmental sample?
Fluorescence microscopy
Quantitative PCR (qPCR)
Gram staining
Catalase test
Explanation - qPCR amplifies specific DNA sequences and measures their abundance in real time, allowing quantification of functional genes.
Correct answer is: Quantitative PCR (qPCR)
Q.25 A major limitation of using pure bacterial cultures for the degradation of complex petroleum mixtures is:
Low tolerance to oxygen
Inability to produce extracellular enzymes
Narrow substrate specificity
Rapid mutation rates
Explanation - Pure cultures often metabolize only a limited range of hydrocarbons, whereas mixed communities can attack a broader spectrum.
Correct answer is: Narrow substrate specificity
Q.26 Which of the following best explains why temperature affects the rate of microbial respiration in soils?
Higher temperature reduces water availability
Enzyme activity increases with temperature up to an optimum
Temperature changes the pH of the soil
Microbes become more motile at low temperatures
Explanation - Enzyme-catalyzed reactions accelerate with temperature until enzymes denature, defining an optimum range for respiration.
Correct answer is: Enzyme activity increases with temperature up to an optimum
Q.27 The presence of which gas in landfill leachate is a strong indicator of active methanogenic activity?
O₂
CO₂
CH₄
N₂O
Explanation - Methanogenic archaea produce methane as the final product of anaerobic decomposition in landfills.
Correct answer is: CH₄
Q.28 In the context of microbial ecology, ‘alpha diversity’ refers to:
Diversity between different ecosystems
Diversity within a single sample or community
Genetic variation in a single organism
Diversity of viral particles only
Explanation - Alpha diversity measures species richness and evenness in a localized environment.
Correct answer is: Diversity within a single sample or community
Q.29 Which microbial group is primarily responsible for the oxidation of sulfide to sulfate in marine sediments?
Methanogens
Sulfate‑reducing bacteria
Sulfur‑oxidizing bacteria
Nitrosomonas
Explanation - These bacteria use sulfide (H₂S) as an electron donor and O₂ or nitrate as an electron acceptor, producing sulfate.
Correct answer is: Sulfur‑oxidizing bacteria
Q.30 A common method for stimulating the growth of pollutant‑degrading microbes in situ is:
Adding high concentrations of chlorine
Injecting nutrients such as nitrogen and phosphorus (biostimulation)
Increasing soil salinity
Applying UV radiation
Explanation - Biostimulation supplies limiting nutrients, encouraging native degraders to proliferate and degrade contaminants.
Correct answer is: Injecting nutrients such as nitrogen and phosphorus (biostimulation)
Q.31 Which of the following is NOT a typical characteristic of extremophilic archaea?
Thermophilic growth at >80 °C
Requirement for high salt concentrations
Presence of chlorophyll a for photosynthesis
Acidophilic tolerance to pH < 2
Explanation - Most extremophilic archaea are non‑photosynthetic; chlorophyll a is associated with plants and cyanobacteria.
Correct answer is: Presence of chlorophyll a for photosynthesis
Q.32 In a wastewater treatment plant, the conversion of organic carbon to CO₂ under aerobic conditions is primarily carried out by:
Anaerobic digesters
Aerobic heterotrophic bacteria
Nitrifying archaea
Denitrifying fungi
Explanation - These bacteria oxidize organic substrates using oxygen, producing CO₂, water, and biomass.
Correct answer is: Aerobic heterotrophic bacteria
Q.33 Which of the following best describes the role of extracellular polymeric substances (EPS) in biofilms?
They act as a nutrient source for neighboring plants
They provide structural stability and protect microbes from environmental stress
They serve as genetic material for horizontal gene transfer
They catalyze the breakdown of pollutants directly
Explanation - EPS form a matrix that holds cells together, retains water, and shields microbes from chemicals and shear forces.
Correct answer is: They provide structural stability and protect microbes from environmental stress
Q.34 The term ‘bioprospecting’ in environmental microbiology refers to:
Searching for new microbial species in extreme habitats for biotechnological applications
Harvesting algae for biofuel production
Monitoring bacterial counts in drinking water
Using microbes to detect earthquakes
Explanation - Bioprospecting explores natural environments to discover organisms that produce valuable enzymes, metabolites, or pathways.
Correct answer is: Searching for new microbial species in extreme habitats for biotechnological applications
Q.35 Which of the following is a characteristic metabolic trait of iron‑reducing bacteria in anoxic sediments?
Oxidizing Fe²⁺ to Fe³⁺
Using Fe³⁺ as an electron acceptor to oxidize organic carbon
Fixing atmospheric nitrogen
Producing methane as a by‑product
Explanation - Iron‑reducing bacteria couple the oxidation of organic compounds to the reduction of ferric iron (Fe³⁺) to ferrous iron (Fe²⁺).
Correct answer is: Using Fe³⁺ as an electron acceptor to oxidize organic carbon
Q.36 In an aerobic composting system, which factor most strongly limits the rate of organic matter degradation?
Oxygen diffusion
Presence of heavy metals
UV radiation
pH below 3
Explanation - Adequate oxygen supply is essential for aerobic microbes to efficiently decompose organic material.
Correct answer is: Oxygen diffusion
Q.37 Which microbial process can convert nitrate (NO₃⁻) directly to nitrogen gas (N₂) without producing nitrite (NO₂⁻) as an intermediate?
Nitrification
Anammox
Denitrification
Ammonification
Explanation - Anaerobic ammonium oxidation (Anammox) combines NH₄⁺ and NO₂⁻ (produced internally) to form N₂, bypassing nitrite accumulation.
Correct answer is: Anammox
Q.38 Which of the following is a common molecular marker used to assess bacterial phylogeny in environmental samples?
16S rRNA gene
Cytochrome c oxidase I gene
ITS region
RbcL gene
Explanation - The 16S rRNA gene contains conserved and variable regions, making it ideal for bacterial identification and phylogeny.
Correct answer is: 16S rRNA gene
Q.39 The ‘critical load’ concept in microbial ecology is used to describe:
The maximum number of microbes a system can sustain
The threshold level of a pollutant beyond which microbial community structure changes irreversibly
The minimum oxygen concentration required for aerobic respiration
The ideal temperature range for microbial growth
Explanation - Critical load defines a pollutant concentration that a microbial ecosystem can tolerate without lasting damage.
Correct answer is: The threshold level of a pollutant beyond which microbial community structure changes irreversibly
Q.40 Which group of microorganisms is most important for the initial decomposition of cellulose in forest soils?
Actinomycetes
Cyanobacteria
Methanogenic archaea
Sulfur‑oxidizing bacteria
Explanation - Actinomycetes produce cellulases that break down cellulose into simpler sugars for further microbial utilization.
Correct answer is: Actinomycetes
Q.41 In the context of bioreactor design, a ‘plug‑flow’ reactor assumes:
Complete mixing of the substrate throughout the vessel
No axial mixing; fluid moves as a ‘plug’ with uniform velocity
Continuous recirculation of the culture
Static batch operation
Explanation - Plug‑flow reactors model ideal behavior where each fluid element experiences the same residence time.
Correct answer is: No axial mixing; fluid moves as a ‘plug’ with uniform velocity
Q.42 Which of the following microorganisms is known for producing the antibiotic streptomycin?
Streptomyces griseus
Bacillus subtilis
Pseudomonas aeruginosa
Escherichia coli
Explanation - Streptomyces griseus, a soil actinomycete, was the original source of streptomycin.
Correct answer is: Streptomyces griseus
Q.43 Which of the following best explains why microbial communities in soils often exhibit high resistance to pesticide exposure?
They rapidly mutate to new species
Horizontal gene transfer spreads degradative plasmids
Pesticides are inert to microbial metabolism
Microbes avoid contaminated zones
Explanation - Plasmids carrying pesticide‑degrading genes can be transferred among bacteria, conferring resistance and degradation capacity.
Correct answer is: Horizontal gene transfer spreads degradative plasmids
Q.44 A key indicator that an anaerobic digester is operating efficiently is:
High concentration of dissolved oxygen
Stable pH around 7.0‑7.5
Accumulation of volatile fatty acids
Elevated temperature above 80 °C
Explanation - Methanogenic activity is optimal at neutral pH; large pH fluctuations signal process imbalance.
Correct answer is: Stable pH around 7.0‑7.5
Q.45 Which of the following statements about 'syntrophic' relationships in microbial communities is correct?
Both partners produce the same end product
One organism consumes the waste products of another, making the overall reaction energetically favorable
Syntrophy only occurs between bacteria and viruses
It requires light as an energy source
Explanation - Syntrophic interactions allow thermodynamically unfavorable reactions to proceed by coupling them with a partner that removes inhibitory products.
Correct answer is: One organism consumes the waste products of another, making the overall reaction energetically favorable
Q.46 Which gas is commonly measured as an indicator of microbial activity in composting operations?
O₂
CO₂
CH₄
N₂O
Explanation - CO₂ production reflects aerobic respiration of compost microbes and is routinely monitored to assess activity.
Correct answer is: CO₂
Q.47 The presence of which functional gene would suggest a microbial community is capable of degrading polycyclic aromatic hydrocarbons (PAHs)?
nirS
amoA
catA
pahA
Explanation - The pahA gene encodes enzymes (e.g., ring‑hydroxylating dioxygenases) involved in PAH catabolism.
Correct answer is: pahA
Q.48 In a lake that undergoes seasonal stratification, the anoxic bottom layer (hypolimnion) is most likely to support which microbial process?
Nitrification
Photosynthesis
Denitrification
Aerobic respiration
Explanation - Anoxic conditions favor denitrifiers that reduce nitrate to nitrogen gases.
Correct answer is: Denitrification
Q.49 Which of the following is an advantage of using next‑generation sequencing (NGS) over traditional culture‑based methods for studying environmental microbes?
NGS can determine the exact metabolic rate of each species
NGS detects both culturable and unculturable organisms, providing a more complete community profile
NGS is less expensive than plate counting
NGS eliminates the need for DNA extraction
Explanation - NGS sequences DNA directly from the environment, capturing the diversity of organisms that cannot be cultured.
Correct answer is: NGS detects both culturable and unculturable organisms, providing a more complete community profile
Q.50 Which microbial process contributes most to the removal of organic pollutants in a conventional activated sludge system?
Anaerobic fermentation
Aerobic heterotrophic oxidation
Nitrification
Methanogenesis
Explanation - Activated sludge relies on aerobic heterotrophs that oxidize organic contaminants to CO₂ and water.
Correct answer is: Aerobic heterotrophic oxidation
Q.51 The term ‘biogeochemical cycling’ refers to:
The movement of geological minerals only
The transformation and movement of elements (e.g., C, N, S) through biological, geological, and chemical processes
The flow of electricity in microbial fuel cells
The spread of viruses in marine environments
Explanation - Biogeochemical cycles integrate microbial metabolism with physical and chemical transformations in ecosystems.
Correct answer is: The transformation and movement of elements (e.g., C, N, S) through biological, geological, and chemical processes
Q.52 Which of the following is a common method for enhancing the bioavailability of hydrophobic pollutants for microbial degradation?
Adding surfactants
Increasing salinity
Lowering pH to <2
Heating to >100 °C
Explanation - Surfactants lower surface tension and increase solubility of hydrophobic compounds, making them more accessible to microbes.
Correct answer is: Adding surfactants
Q.53 In the context of microbial ecology, ‘r‑strategists’ are characterized by:
Slow growth and high stress tolerance
Rapid growth, high reproductive rates, and preference for nutrient‑rich environments
Obligate symbiosis with plants
Production of large amounts of extracellular polymeric substances
Explanation - r‑strategists thrive in disturbed, resource‑abundant habitats, reproducing quickly to exploit available niches.
Correct answer is: Rapid growth, high reproductive rates, and preference for nutrient‑rich environments
Q.54 Which microbial group is primarily responsible for the conversion of sulfates to sulfides in anoxic marine sediments?
Sulfur‑oxidizing bacteria
Sulfate‑reducing bacteria
Methanogens
Nitrifiers
Explanation - Sulfate‑reducing bacteria use SO₄²⁻ as an electron acceptor, producing H₂S during anaerobic respiration.
Correct answer is: Sulfate‑reducing bacteria
Q.55 Which of the following statements about microbial mats in hot springs is correct?
They consist solely of thermophilic archaea
They are layered communities where different metabolic groups occupy specific niches
They are only found in freshwater environments
They cannot perform photosynthesis
Explanation - Microbial mats display vertical stratification: photosynthetic cyanobacteria on top, anaerobes (e.g., sulfate reducers) deeper down.
Correct answer is: They are layered communities where different metabolic groups occupy specific niches
Q.56 Which of the following is a primary limitation when using molecular fingerprinting (e.g., DGGE) to assess microbial community structure?
Inability to detect any unculturable organisms
Low resolution for detecting rare species
Requires live cells only
Provides quantitative abundance data
Explanation - DGGE and similar techniques favor dominant DNA fragments, often missing low‑abundance members of the community.
Correct answer is: Low resolution for detecting rare species
Q.57 What is the main ecological function of nitrogen‑fixing cyanobacteria in rice paddies?
Decomposing dead plant material
Providing a source of fixed nitrogen to the crop
Producing methane for energy
Reducing soil salinity
Explanation - Cyanobacterial heterocysts host nitrogenase, converting atmospheric N₂ into ammonia that can be used by rice plants.
Correct answer is: Providing a source of fixed nitrogen to the crop
Q.58 In an oil‑contaminated aquifer, which of the following would most likely be the limiting factor for microbial degradation?
Presence of oxygen
Water temperature above 50 °C
High concentrations of heavy metals
Excessive light exposure
Explanation - Aerobic hydrocarbon degraders require dissolved oxygen; limited O₂ often constrains biodegradation rates.
Correct answer is: Presence of oxygen
Q.59 Which of the following best explains why the 16S rRNA gene is conserved across bacterial species?
It encodes a structural component of the ribosome essential for protein synthesis
It is involved in DNA replication
It determines cell wall composition
It regulates flagellar motility
Explanation - The 16S rRNA is a ribosomal RNA subunit; its essential role leads to high conservation, making it a reliable phylogenetic marker.
Correct answer is: It encodes a structural component of the ribosome essential for protein synthesis
Q.60 Which microbial metabolic pathway is directly involved in the production of nitrous oxide (N₂O) in soils?
Nitrification
Denitrification
Anammox
Methanogenesis
Explanation - During denitrification, N₂O is an intermediate that can be released before being reduced to N₂.
Correct answer is: Denitrification
Q.61 A major advantage of using immobilized microbial cells in bioreactors is:
Higher susceptibility to shear stress
Reduced risk of cell washout and higher cell density
Complete elimination of by‑product formation
Ability to operate at any temperature
Explanation - Immobilization retains cells within the reactor, allowing high biomass concentrations and preventing loss with the effluent.
Correct answer is: Reduced risk of cell washout and higher cell density
Q.62 Which of the following is a common indicator of microbial iron oxidation in freshwater streams?
Formation of orange‑brown iron precipitates (iron oxyhydroxides)
Production of bright green algae blooms
Decrease in water hardness
Increase in dissolved oxygen levels
Explanation - Iron‑oxidizing bacteria convert Fe²⁺ to Fe³⁺, which precipitates as ferric oxyhydroxides, giving a characteristic coloration.
Correct answer is: Formation of orange‑brown iron precipitates (iron oxyhydroxides)
Q.63 In the context of environmental microbiology, the term ‘bioindicator’ refers to:
A device that measures pH
A species or microbial community whose presence, absence, or abundance reflects a specific environmental condition
A chemical that kills all microbes in a sample
A mathematical model of population dynamics
Explanation - Bioindicators are used to assess ecosystem health, pollution levels, or changes in environmental parameters.
Correct answer is: A species or microbial community whose presence, absence, or abundance reflects a specific environmental condition
Q.64 Which of the following is the most effective method for reducing the population of pathogenic bacteria in drinking water?
Filtration through sand only
Chlorination
Adding nutrients to promote bacterial growth
Increasing temperature to 30 °C
Explanation - Chlorine is a strong disinfectant that inactivates a wide range of pathogenic microorganisms in water.
Correct answer is: Chlorination
Q.65 The process by which microorganisms transfer electrons to insoluble metal oxides in sediments is called:
Photolysis
Extracellular electron transfer (EET)
Fermentation
Chemotaxis
Explanation - EET enables microbes to respire using solid-phase electron acceptors like Fe(III) oxides, important in geochemical cycling.
Correct answer is: Extracellular electron transfer (EET)
Q.66 Which microbial process is primarily responsible for the formation of humus in soil?
Methanogenesis
Decomposition of lignin and complex polymers by fungi and actinomycetes
Nitrification
Anammox
Explanation - Fungi and actinomycetes break down complex organic matter, producing stable humic substances that contribute to humus.
Correct answer is: Decomposition of lignin and complex polymers by fungi and actinomycetes
Q.67 A major ecological consequence of excessive nitrogen fertilizer use is:
Increased soil acidity only
Eutrophication of nearby water bodies due to runoff
Decrease in microbial diversity in the rhizosphere
Immediate increase in methane emissions
Explanation - Leached nitrates promote algal blooms, depleting oxygen and harming aquatic ecosystems.
Correct answer is: Eutrophication of nearby water bodies due to runoff
Q.68 Which of the following statements about the ‘rare biosphere’ is true?
It consists of the most abundant microbial taxa
It includes low‑abundance species that can become dominant under changing environmental conditions
It refers to viruses only
It is irrelevant to ecosystem functioning
Explanation - The rare biosphere harbors microbial diversity that may be activated when conditions favor their growth.
Correct answer is: It includes low‑abundance species that can become dominant under changing environmental conditions
Q.69 Which of the following is a key factor influencing the rate of anaerobic digestion in a biogas plant?
Light intensity
C/N (carbon to nitrogen) ratio of the feedstock
Wind speed
Presence of ultraviolet radiation
Explanation - An optimal C/N ratio (typically 20‑30) balances microbial nutrition, preventing ammonia inhibition or carbon limitation.
Correct answer is: C/N (carbon to nitrogen) ratio of the feedstock
Q.70 In a laboratory experiment, a researcher adds a broad‑spectrum antibiotic to a soil microcosm. The most likely immediate effect on the microbial community is:
Increase in overall microbial diversity
Selective reduction of susceptible bacteria, potentially allowing resistant strains to dominate
Immediate rise in methane production
Complete sterilization of the soil
Explanation - Antibiotics suppress sensitive taxa, giving resistant organisms a competitive advantage.
Correct answer is: Selective reduction of susceptible bacteria, potentially allowing resistant strains to dominate
Q.71 Which of the following is a hallmark of a healthy rhizosphere microbial community?
Dominance of a single bacterial species
High functional redundancy and diverse metabolic capabilities
Absence of fungi
Very low microbial biomass
Explanation - Diverse, redundant functions provide resilience and support plant health through nutrient cycling and disease suppression.
Correct answer is: High functional redundancy and diverse metabolic capabilities
Q.72 Which of the following processes can lead to the release of volatile organic compounds (VOCs) from soils?
Photosynthesis
Aerobic microbial degradation of organic matter
Denitrification
Anaerobic ammonium oxidation
Explanation - Microbial metabolism can produce VOCs such as ethanol, acetone, and other low‑molecular‑weight compounds during aerobic breakdown.
Correct answer is: Aerobic microbial degradation of organic matter
Q.73 The term ‘metabolomics’ in environmental microbiology refers to:
Sequencing of microbial genomes
Analysis of the complete set of metabolites produced by a microbial community
Measuring the rate of gas exchange in soils
Studying the morphology of microbes under a microscope
Explanation - Metabolomics profiles the small molecules present, giving insight into functional activity of microbes.
Correct answer is: Analysis of the complete set of metabolites produced by a microbial community
Q.74 Which of the following best explains why some bacteria can survive extreme desiccation in desert soils?
They possess thick peptidoglycan layers that retain water
They produce protective extracellular polysaccharide matrices and enter dormant states
They continuously synthesize new DNA to replace lost water
They rely on photosynthesis for water production
Explanation - Desiccation‑tolerant bacteria form protective biofilms and can form spores or dormant cells to endure dry periods.
Correct answer is: They produce protective extracellular polysaccharide matrices and enter dormant states
Q.75 In a river impacted by agricultural runoff, an increase in which microbial indicator is most likely to be observed?
Thermophilic bacteria
Fecal coliforms
Sulfur‑oxidizing bacteria
Methanogens
Explanation - Runoff often carries animal waste, introducing fecal coliforms that serve as indicators of contamination.
Correct answer is: Fecal coliforms
Q.76 Which of the following is a common use of genetically engineered microbes in environmental biotechnology?
Producing high‑yield wheat varieties
Degrading persistent organic pollutants such as polychlorinated biphenyls (PCBs)
Increasing atmospheric CO₂ levels
Enhancing the taste of bottled water
Explanation - Engineered microbes can express enzymes that break down recalcitrant chemicals, aiding bioremediation.
Correct answer is: Degrading persistent organic pollutants such as polychlorinated biphenyls (PCBs)
Q.77 Which of the following statements about the 'Redfield Ratio' is correct?
It describes the optimal C:N:P ratio (106:16:1) for marine phytoplankton growth
It defines the ratio of oxygen to nitrogen in the atmosphere
It is used to calculate the pH of soils
It measures the electrical conductivity of water
Explanation - The Redfield Ratio reflects the average elemental composition of marine biomass and guides nutrient dynamics studies.
Correct answer is: It describes the optimal C:N:P ratio (106:16:1) for marine phytoplankton growth
Q.78 Which of the following microbial processes is directly responsible for the conversion of CO₂ into organic matter in aquatic ecosystems?
Methanogenesis
Chemoautotrophy
Photosynthesis by cyanobacteria and algae
Denitrification
Explanation - Photosynthetic microbes fix CO₂ using light energy, producing organic carbon that fuels the food web.
Correct answer is: Photosynthesis by cyanobacteria and algae
Q.79 When evaluating the potential of a microbial consortium for degrading a novel pollutant, which parameter is most critical to assess first?
The consortium's color under the microscope
The growth rate of each member on a standard carbon source
The ability of the consortium to metabolize the target pollutant as a sole carbon source
The temperature tolerance of the consortium
Explanation - Demonstrating that the community can use the pollutant for growth is essential before optimizing other conditions.
Correct answer is: The ability of the consortium to metabolize the target pollutant as a sole carbon source