Q.1 What is the typical shape of a bacterial growth curve in a closed system?
Linear
S‑shaped
Parabolic
Exponential only
Explanation - In a closed system bacterial growth follows a sigmoidal or S‑shaped curve with lag, exponential, stationary, and death phases.
Correct answer is: S‑shaped
Q.2 Which phase follows the lag phase in bacterial growth?
Exponential phase
Stationary phase
Death phase
Lag phase continues
Explanation - After the lag phase bacteria begin to divide rapidly during the exponential (log) phase.
Correct answer is: Exponential phase
Q.3 What is the main energy source for heterotrophic bacteria?
Glucose
CO₂
Light
Oxygen
Explanation - Heterotrophic bacteria obtain both carbon and energy from organic molecules like glucose.
Correct answer is: Glucose
Q.4 Which of the following nutrients is NOT required by most bacteria?
Carbon
Nitrogen
Water
Silicon
Explanation - Silicon is not a common nutrient requirement for bacterial growth; carbon, nitrogen, and water are essential.
Correct answer is: Silicon
Q.5 What type of media is used to isolate single colonies on agar?
Liquid media
Dilution agar
Solid agar
Co-culture media
Explanation - Solid agar allows individual colonies to grow in isolation, facilitating isolation of pure strains.
Correct answer is: Solid agar
Q.6 The ability of a bacterium to grow in the presence of a specific substrate indicates what?
Its metabolic versatility
Its resistance to antibiotics
Its motility
Its spore formation
Explanation - Growth on a substrate shows the organism can metabolize that compound, reflecting metabolic flexibility.
Correct answer is: Its metabolic versatility
Q.7 Which of the following factors most strongly influences the rate of bacterial growth?
Temperature
Light intensity
Sound frequency
Earth's magnetic field
Explanation - Temperature affects enzyme activity and membrane fluidity, directly impacting growth rates.
Correct answer is: Temperature
Q.8 What is the purpose of a selective medium?
To grow all microorganisms
To isolate a specific group of microorganisms
To provide only carbon
To measure pH changes
Explanation - Selective media contain inhibitors that suppress unwanted organisms while allowing desired ones to grow.
Correct answer is: To isolate a specific group of microorganisms
Q.9 Which nutrient is essential for the synthesis of nucleic acids in bacteria?
Vitamins
Amino acids
Nucleotides
Fatty acids
Explanation - Nucleotides are the building blocks of DNA and RNA, essential for genetic material synthesis.
Correct answer is: Nucleotides
Q.10 What does the term 'autotroph' mean in the context of bacterial nutrition?
Consumes organic matter only
Obtains carbon from CO₂
Requires antibiotics
Forms spores
Explanation - Autotrophic bacteria fix inorganic carbon (CO₂) for their carbon needs.
Correct answer is: Obtains carbon from CO₂
Q.11 Which of the following is a characteristic of a fastidious bacterium?
Grows on minimal media
Requires specific growth factors
Is resistant to heat
Lacks cell walls
Explanation - Fastidious organisms need particular vitamins or amino acids not found in standard media.
Correct answer is: Requires specific growth factors
Q.12 During the stationary phase, bacterial cells mainly engage in which activity?
Rapid division
Spore formation
Metabolic maintenance and stress response
Photosynthesis
Explanation - In the stationary phase growth stops, and cells focus on maintenance and defense.
Correct answer is: Metabolic maintenance and stress response
Q.13 Which of the following is a primary source of energy for photosynthetic bacteria?
Glucose
Sunlight
Nitrate
Oxygen
Explanation - Photosynthetic bacteria harness light energy to drive cellular reactions.
Correct answer is: Sunlight
Q.14 What is the function of a differential medium?
To select specific organisms
To differentiate between organisms based on a specific biochemical property
To grow only fungi
To sterilize samples
Explanation - Differential media contain indicators that reveal metabolic differences among bacteria.
Correct answer is: To differentiate between organisms based on a specific biochemical property
Q.15 Which compound is commonly used as a carbon source in nutrient agar?
Starch
Glucose
Lactose
Sucrose
Explanation - Glucose is a simple sugar readily metabolized by many bacteria.
Correct answer is: Glucose
Q.16 The presence of which gas indicates anaerobic bacterial growth?
O₂
CO₂
H₂S
N₂O
Explanation - Anaerobes often produce CO₂, which can be detected in closed tubes or indicator media.
Correct answer is: CO₂
Q.17 Why is peptone added to bacterial growth media?
Provides vitamins
Provides inorganic salts
Provides nitrogen and growth factors
Provides carbon
Explanation - Peptone supplies amino acids, peptides, and nitrogen essential for growth.
Correct answer is: Provides nitrogen and growth factors
Q.18 Which of the following best describes 'nutrient broth'?
A selective medium
A differential medium
A general-purpose liquid medium
A solid medium
Explanation - Nutrient broth contains nutrients that support growth of most non-fastidious bacteria.
Correct answer is: A general-purpose liquid medium
Q.19 Which of the following is a primary source of inorganic nitrogen for bacteria?
Nitrate
Glucose
Lactose
Sodium chloride
Explanation - Nitrate can be used by many bacteria as a nitrogen source and electron acceptor.
Correct answer is: Nitrate
Q.20 Which term refers to a culture that contains only one type of microorganism?
Mixed culture
Pure culture
Complex culture
Synergistic culture
Explanation - A pure culture has a single microbial species, essential for experimental consistency.
Correct answer is: Pure culture
Q.21 What is the effect of increasing the concentration of NaCl in a medium on bacterial growth?
Always promotes growth
Always inhibits growth
Depends on the bacterial species' salt tolerance
Has no effect
Explanation - Halophiles thrive in high salt, whereas most bacteria are inhibited by high NaCl.
Correct answer is: Depends on the bacterial species' salt tolerance
Q.22 Which of the following is a common indicator for pH in a differential medium?
Xanthine
Methylene blue
Phenol red
Osmotic pressure
Explanation - Phenol red changes color with pH, indicating acid/base production by bacteria.
Correct answer is: Phenol red
Q.23 Which nutrient is specifically required for the growth of Mycobacterium species?
Iron
Nicotinamide adenine dinucleotide (NAD)
Copper
Silicon
Explanation - Mycobacteria cannot synthesize NAD and require it as a growth factor in culture media.
Correct answer is: Nicotinamide adenine dinucleotide (NAD)
Q.24 What is the purpose of adding agar to a liquid medium?
To make it selective
To increase pH
To solidify the medium
To provide nutrients
Explanation - Agar acts as a gelling agent, turning liquid media into solid agar plates.
Correct answer is: To solidify the medium
Q.25 Which of the following statements is TRUE about facultative anaerobes?
They can only grow in oxygen
They can only grow in the absence of oxygen
They can grow with or without oxygen
They are obligate parasites
Explanation - Facultative anaerobes switch metabolic pathways depending on oxygen availability.
Correct answer is: They can grow with or without oxygen
Q.26 The presence of which element is vital for the synthesis of the bacterial cell wall peptidoglycan?
Calcium
Iron
Zinc
Magnesium
Explanation - Calcium ions stabilize the peptidoglycan layer and are involved in cell division.
Correct answer is: Calcium
Q.27 What does the term 'nutrient limitation' refer to in bacterial culture?
Excess nutrients
No nutrients
Insufficient nutrients for optimal growth
Unlimited energy
Explanation - Nutrient limitation occurs when a required growth component is below the necessary level.
Correct answer is: Insufficient nutrients for optimal growth
Q.28 Which of the following media is best for detecting lactose fermentation?
MacConkey agar
Blood agar
Chloramphenicol agar
Chocolate agar
Explanation - MacConkey agar contains lactose and a pH indicator to distinguish lactose fermenters.
Correct answer is: MacConkey agar
Q.29 Which enzyme is involved in the breakdown of glucose in aerobic bacterial respiration?
Hexokinase
Lactase
Glucuronidase
Alkaline phosphatase
Explanation - Hexokinase phosphorylates glucose, initiating glycolysis in aerobic respiration.
Correct answer is: Hexokinase
Q.30 The ability of a bacterium to grow at 4°C indicates what?
Heat tolerance
Psychrophilic adaptation
Extreme alkalinity tolerance
Phototrophy
Explanation - Growth at low temperatures indicates a psychrophilic organism.
Correct answer is: Psychrophilic adaptation
Q.31 Which of the following is NOT a typical nutrient in enriched media like blood agar?
Hemoglobin
Lysed red cells
Amino acids
Iron salts
Explanation - Blood agar relies on hemoglobin and lysed red cells; iron salts are not a main component.
Correct answer is: Iron salts
Q.32 What role does the enzyme urease play in bacterial metabolism?
Breaks down urea into ammonia and CO₂
Synthesizes ribosomal RNA
Catalyzes fatty acid synthesis
Degrades antibiotics
Explanation - Urease hydrolyzes urea, providing nitrogen and increasing local pH.
Correct answer is: Breaks down urea into ammonia and CO₂
Q.33 Which of the following is an example of a fast-growing bacterium?
Mycobacterium tuberculosis
Escherichia coli
Streptococcus pyogenes
Listeria monocytogenes
Explanation - E. coli divides rapidly under favorable conditions, making it a model fast grower.
Correct answer is: Escherichia coli
Q.34 Which of the following best describes an 'extremophile'?
An organism that requires high temperature
An organism that thrives in extreme environments
An organism that is a pathogen
An organism that photosynthesizes
Explanation - Extremophiles grow in conditions (temperature, pH, salinity) that are hostile to most life.
Correct answer is: An organism that thrives in extreme environments
Q.35 Which of the following media is selective for Gram‑positive cocci?
MacConkey agar
Chocolate agar
Mannitol salt agar
Sabouraud agar
Explanation - High salt concentration inhibits Gram‑negative bacteria, favoring Gram‑positive cocci.
Correct answer is: Mannitol salt agar
Q.36 What does 'autolysis' refer to in bacterial cell biology?
Cell division
Cell death due to self‑enzymatic degradation
Spore formation
Protein synthesis
Explanation - Autolysis occurs when bacterial enzymes break down the cell wall from within.
Correct answer is: Cell death due to self‑enzymatic degradation
Q.37 The addition of which vitamin is crucial for the growth of many fastidious bacteria?
Vitamin C
Vitamin D
Vitamin B12
Vitamin K
Explanation - Vitamin B12 (cobalamin) is a growth factor for several fastidious organisms.
Correct answer is: Vitamin B12
Q.38 Which of the following best describes the 'death phase' in bacterial growth?
Rapid increase in cell number
Plateau in growth
Decrease in cell viability over time
Spore formation
Explanation - During the death phase, cell death surpasses replication, leading to a net loss of viable cells.
Correct answer is: Decrease in cell viability over time
Q.39 What is the main role of the electron transport chain in bacteria?
Synthesize amino acids
Generate ATP
Repair DNA
Produce cell wall
Explanation - The electron transport chain produces a proton gradient used to synthesize ATP via chemiosmosis.
Correct answer is: Generate ATP
Q.40 Which of the following indicates that a bacterial species is a 'pathogen'?
It can be cultured on nutrient agar
It causes disease in a host
It is Gram‑negative
It forms spores
Explanation - A pathogen is defined by its ability to cause disease.
Correct answer is: It causes disease in a host
Q.41 Which component of the cell membrane is essential for bacterial survival?
Chlorophyll
Lipid bilayer
DNA
Protein only
Explanation - The lipid bilayer provides structural integrity and regulates transport.
Correct answer is: Lipid bilayer
Q.42 Which of the following best explains why anaerobic bacteria may produce gas during culture?
They perform photosynthesis
They metabolize carbohydrates producing CO₂ or H₂
They generate oxygen internally
They consume gas
Explanation - Anaerobic fermentation results in gas production as a metabolic by‑product.
Correct answer is: They metabolize carbohydrates producing CO₂ or H₂
Q.43 Why is it important to keep a bacterial culture in the exponential phase for experiments?
To ensure uniform growth conditions
To avoid spore formation
Because all bacteria die after exponential phase
To maximize antibiotic resistance
Explanation - Exponential phase represents steady, active growth, minimizing variability.
Correct answer is: To ensure uniform growth conditions
Q.44 Which of the following is a typical indicator used to detect nitrate reduction in bacterial culture?
Sulfadiazine
Nitrate broth with sulfanilamide and diphenylamine
Methylene blue
Phenol red
Explanation - This reagent turns purple when nitrite is formed, indicating nitrate reduction.
Correct answer is: Nitrate broth with sulfanilamide and diphenylamine
Q.45 Which of the following best describes a 'saprophytic' microorganism?
It obtains nutrients from living hosts
It feeds on dead organic matter
It requires oxygen exclusively
It produces spores
Explanation - Saprophytes degrade dead material, obtaining energy and nutrients from it.
Correct answer is: It feeds on dead organic matter
Q.46 Which of the following is essential for the synthesis of bacterial DNA?
ATP
NAD
Nucleotides
Glucose
Explanation - DNA is built from nucleotides, which must be available for replication.
Correct answer is: Nucleotides
Q.47 The growth of bacteria in a culture with high glucose concentration is limited by which factor?
Oxygen depletion
Osmotic stress
Temperature
Light
Explanation - High sugar concentrations create high osmotic pressure, inhibiting growth.
Correct answer is: Osmotic stress
Q.48 What is the significance of a 'colonial morphology' observed on agar plates?
It indicates the age of the culture
It can help differentiate bacterial species
It shows the pH of the medium
It measures antibiotic resistance
Explanation - Colony appearance (size, color, shape) provides clues to identity.
Correct answer is: It can help differentiate bacterial species
Q.49 Which of the following is NOT a requirement for bacterial growth?
Carbon source
Oxygen
Water
Nitrogen source
Explanation - While some bacteria require oxygen, many are anaerobes and can grow without it.
Correct answer is: Oxygen
Q.50 In the context of media, what does 'dilution agar' refer to?
A medium with high salt concentration
A medium used to isolate individual colonies by serial dilution
A liquid broth that is diluted for testing
A selective medium for fungi
Explanation - Dilution agar helps isolate colonies by limiting bacterial numbers per area.
Correct answer is: A medium used to isolate individual colonies by serial dilution
Q.51 Which of the following best describes the function of an 'indicator' in differential media?
To kill unwanted organisms
To reveal metabolic changes via color shift
To provide nutrients
To maintain pH
Explanation - Indicators change color in response to metabolic by‑products, enabling differentiation.
Correct answer is: To reveal metabolic changes via color shift
Q.52 Which of the following bacteria is known for its requirement of cysteine in growth media?
Staphylococcus aureus
Clostridium difficile
Streptococcus pyogenes
Bacillus subtilis
Explanation - C. difficile is a strict anaerobe that requires cysteine as a growth factor.
Correct answer is: Clostridium difficile
Q.53 What is the role of 'Mg²⁺' in bacterial enzymatic reactions?
It acts as a structural component of the cell membrane
It stabilizes ribosomes and enzyme active sites
It provides energy
It functions as a pH buffer
Explanation - Magnesium ions are essential cofactors for many enzymes and ribosomal stability.
Correct answer is: It stabilizes ribosomes and enzyme active sites
Q.54 Which of the following describes a 'chemoheterotroph'?
Obtains energy from light
Obtains both carbon and energy from organic compounds
Obtains energy from inorganic compounds
Obtains carbon from CO₂ and energy from light
Explanation - Chemoheterotrophs rely on organic molecules for both carbon and energy.
Correct answer is: Obtains both carbon and energy from organic compounds
Q.55 The presence of which of the following indicates a bacterial culture is in the stationary phase?
High rate of division
Low pH of the medium
No change in population density
Rapid increase in temperature
Explanation - During stationary phase the growth rate equals the death rate, stabilizing the population.
Correct answer is: No change in population density
Q.56 Which of the following is a primary benefit of using a solid medium?
It allows observation of colony morphology
It provides no nutrients
It prevents bacterial growth
It is only for fungi
Explanation - Solid media enable isolation of colonies and visual assessment of their characteristics.
Correct answer is: It allows observation of colony morphology
Q.57 Which of the following best defines an 'oligotrophic' environment?
Rich in nutrients
Low in nutrients
High in oxygen
High temperature
Explanation - Oligotrophic environments have low levels of organic nutrients, limiting microbial growth.
Correct answer is: Low in nutrients
Q.58 Which of the following is an essential cofactor for bacterial ribosomal protein synthesis?
Iron
Vitamin B2 (riboflavin)
Vitamin C
Vitamin B12
Explanation - Riboflavin is required for the synthesis of FMN and FAD, cofactors in many metabolic pathways.
Correct answer is: Vitamin B2 (riboflavin)
Q.59 What is the primary function of the bacterial capsule?
Energy storage
Protection against phagocytosis
Cell division
Motility
Explanation - The capsule shields bacteria from host immune cells and desiccation.
Correct answer is: Protection against phagocytosis
Q.60 Which of the following is a hallmark of a 'biofilm'?
Free-floating cells
Cells embedded in extracellular polymeric substances
Cells lacking a cell wall
Cells that form spores
Explanation - Biofilms are communities of microbes encased in a self-produced matrix.
Correct answer is: Cells embedded in extracellular polymeric substances
Q.61 Which of the following best describes a 'non‑spore‑forming' bacterium?
It can only grow in anaerobic conditions
It does not produce spores under stress
It requires spores to initiate growth
It always forms spores
Explanation - Non-spore-formers lack the ability to form endospores during adverse conditions.
Correct answer is: It does not produce spores under stress
Q.62 In bacterial growth studies, what is a 'CFU'?
Colony Forming Unit
Cellular Fluorescent Unit
Carbon Fuel Unit
Control Factor Unit
Explanation - CFU quantifies viable bacterial cells capable of forming colonies.
Correct answer is: Colony Forming Unit
Q.63 Which of the following is a key feature of 'Gram‑negative' bacteria?
Thick peptidoglycan layer
Thin peptidoglycan layer with an outer membrane
No cell wall
Only one type of flagellum
Explanation - Gram‑negative bacteria have a thin peptidoglycan surrounded by an outer membrane.
Correct answer is: Thin peptidoglycan layer with an outer membrane
Q.64 Which of the following best explains why anaerobes often produce hydrogen sulfide (H₂S) in culture?
They use H₂S as an energy source
They reduce sulfite or thiosulfate to H₂S
They cannot metabolize sulfur
They generate oxygen
Explanation - Anaerobes can use sulfur compounds as electron acceptors, producing H₂S.
Correct answer is: They reduce sulfite or thiosulfate to H₂S
Q.65 Which of the following is NOT a typical growth factor required by fastidious bacteria?
Heme
Nicotinamide adenine dinucleotide (NAD)
Cysteine
Calcium carbonate
Explanation - Fastidious bacteria often require heme, NAD, or cysteine; calcium carbonate is not a growth factor.
Correct answer is: Calcium carbonate
Q.66 Which of the following indicates that a bacterium is a 'facultative anaerobe'?
It can grow only in the presence of oxygen
It can grow only in the absence of oxygen
It can grow with or without oxygen
It requires high temperature
Explanation - Facultative anaerobes switch metabolic pathways depending on oxygen availability.
Correct answer is: It can grow with or without oxygen
Q.67 Which of the following best describes the role of 'fermentation' in bacterial metabolism?
Production of ATP in presence of oxygen
Production of ATP without oxygen using organic substrates
Synthesis of DNA
Synthesis of fatty acids
Explanation - Fermentation allows anaerobic ATP production by metabolizing organic molecules.
Correct answer is: Production of ATP without oxygen using organic substrates
Q.68 Which of the following is a typical feature of 'Gram‑positive' bacteria?
Outer membrane
Thick peptidoglycan layer
Thin peptidoglycan layer
No peptidoglycan
Explanation - Gram‑positive bacteria retain crystal violet due to a thick peptidoglycan wall.
Correct answer is: Thick peptidoglycan layer
Q.69 Which of the following is an example of a 'nutrient‑rich' medium?
M9 minimal medium
Nutrient broth
Water
Pure water with glucose
Explanation - Nutrient broth contains many organic and inorganic nutrients supporting fast growth.
Correct answer is: Nutrient broth
Q.70 In a bacterial growth curve, what causes the transition from exponential to stationary phase?
Excess nutrients
Oxygen saturation
Cell death exceeding division
Temperature increase
Explanation - When nutrients deplete and waste accumulates, death balances growth, creating stationary phase.
Correct answer is: Cell death exceeding division
Q.71 Which of the following is a key requirement for bacterial DNA replication?
ATP
DNA polymerase
Glucose
Oxygen
Explanation - DNA polymerase is essential for synthesizing new DNA strands during replication.
Correct answer is: DNA polymerase
Q.72 Which of the following media contains bile salts to isolate enteric bacteria?
MacConkey agar
Blood agar
Chocolate agar
Mannitol salt agar
Explanation - Bile salts in MacConkey agar inhibit Gram‑positive bacteria, favoring enterics.
Correct answer is: MacConkey agar
Q.73 Which of the following best explains the term 'pH indicator' in media?
A compound that changes color in response to pH changes
A nutrient source
A selective agent
A preservative
Explanation - pH indicators reveal acid or base production by microbes via color change.
Correct answer is: A compound that changes color in response to pH changes
Q.74 Which of the following is a typical feature of a 'psychrophile'?
Optimal growth at 60°C
Optimal growth at 0–15°C
Optimal growth at 30–37°C
Requires high salt
Explanation - Psychrophiles thrive in cold environments, with optimal growth below 20°C.
Correct answer is: Optimal growth at 0–15°C
Q.75 Which of the following is an example of a 'chemoorganotroph'?
Photosynthetic algae
Bacteria that use organic compounds for energy
Plants that fix CO₂
Nitrifying bacteria
Explanation - Chemoorganotrophs oxidize organic molecules for energy and carbon.
Correct answer is: Bacteria that use organic compounds for energy
Q.76 Which of the following is required for bacterial flagellar motility?
ATP
Bacterioferritin
Calcium carbonate
Chlorophyll
Explanation - The flagellar motor uses ATP (or proton motive force) to drive rotation.
Correct answer is: ATP
Q.77 In a nutrient broth culture, which of the following is likely to happen during the death phase?
Increased cell division
Decreased cell number
Stable cell number
Formation of spores
Explanation - During death phase, the number of viable cells decreases due to nutrient depletion.
Correct answer is: Decreased cell number
Q.78 Which of the following indicates that a bacterium is an obligate aerobe?
It can grow without oxygen
It requires oxygen for growth
It thrives at 4°C
It forms spores in air
Explanation - Obligate aerobes cannot grow without oxygen.
Correct answer is: It requires oxygen for growth
Q.79 What is the main role of 'trace elements' in bacterial media?
Serve as growth inhibitors
Provide structural support
Act as co‑enzymatic cofactors
Change pH
Explanation - Trace elements like iron and zinc are essential for enzyme function.
Correct answer is: Act as co‑enzymatic cofactors
Q.80 Which of the following best describes an 'oligotrophic' organism?
Requires high nutrients
Requires low nutrients
Requires high temperatures
Requires high salinity
Explanation - Oligotrophic organisms thrive in environments with low nutrient availability.
Correct answer is: Requires low nutrients
Q.81 Which of the following is NOT a typical component of a bacterial culture media?
Carbon source
Energy source
Inhibitor
Growth factor
Explanation - Inhibitors are added to selective media but are not core components of general media.
Correct answer is: Inhibitor
Q.82 Which of the following is a key factor determining the optimal growth temperature for bacteria?
Humidity
Light intensity
Water activity
Enzyme kinetics
Explanation - Temperature affects enzyme activity, which in turn influences growth rates.
Correct answer is: Enzyme kinetics
Q.83 Which of the following indicates that a bacterial culture has entered the 'lag phase'?
Rapid division
No visible colonies on agar
Maximum biomass
Production of spores
Explanation - During lag phase, cells adapt to the environment, showing little growth initially.
Correct answer is: No visible colonies on agar
Q.84 Which of the following is a characteristic of a 'chemoorganoautotroph'?
Uses organic compounds for both energy and carbon
Uses inorganic compounds for energy and organic compounds for carbon
Uses light for energy and inorganic CO₂ for carbon
Uses inorganic compounds for energy and CO₂ for carbon
Explanation - Chemoorganoautotrophs oxidize organic molecules for energy and fix CO₂ as carbon source.
Correct answer is: Uses organic compounds for both energy and carbon
Q.85 Which of the following is a typical effect of adding antibiotics to a bacterial culture?
Enhances growth
Selects for resistant mutants
Increases pH
Provides nutrients
Explanation - Antibiotics inhibit susceptible cells, allowing resistant ones to grow.
Correct answer is: Selects for resistant mutants
Q.86 Which of the following best describes a 'minimal medium'?
Contains all possible nutrients
Contains only essential nutrients for a specific organism
Contains no nutrients
Contains only carbon source
Explanation - Minimal media provide only the necessary salts, carbon, and nitrogen for growth.
Correct answer is: Contains only essential nutrients for a specific organism
Q.87 What is the function of 'nitrite broth' in bacterial testing?
Detects nitrate reduction
Detects urease activity
Detects acid production
Detects gas production
Explanation - Nitrite broth changes color if nitrite is produced from nitrate reduction.
Correct answer is: Detects nitrate reduction
Q.88 Which of the following best explains why some bacteria require a 'complex medium' for growth?
They can produce all required nutrients themselves
They lack the biosynthetic pathways for certain vitamins or amino acids
They need high salt concentration
They grow only in the presence of light
Explanation - Fastidious bacteria cannot synthesize some essential growth factors and need complex media.
Correct answer is: They lack the biosynthetic pathways for certain vitamins or amino acids
Q.89 Which of the following best describes the term 'autotroph'?
Consumes organic matter only
Obtains carbon from CO₂
Requires antibiotics
Forms spores
Explanation - Autotrophic bacteria fix inorganic carbon (CO₂) for their carbon needs.
Correct answer is: Obtains carbon from CO₂
Q.90 What is a primary advantage of using 'solid media' for bacterial isolation?
It allows measurement of growth rate
It enables the separation of individual colonies
It prevents bacterial contamination
It is only for fungi
Explanation - Solid media provide a surface where each colony originates from a single cell.
Correct answer is: It enables the separation of individual colonies
Q.91 Which of the following is an example of a 'chemoheterotroph'?
Obtains energy from light
Obtains both carbon and energy from organic compounds
Obtains energy from inorganic compounds
Obtains carbon from CO₂ and energy from light
Explanation - Chemoheterotrophs rely on organic molecules for both carbon and energy.
Correct answer is: Obtains both carbon and energy from organic compounds
Q.92 Which of the following nutrients is essential for DNA synthesis in bacteria?
Glucose
Amino acids
Nucleotides
Vitamins
Explanation - DNA synthesis requires nucleotides as building blocks.
Correct answer is: Nucleotides
Q.93 Which of the following best defines a 'fastidious' bacterium?
Requires minimal nutrients
Requires specific growth factors or vitamins
Can grow in high salt concentrations
Lacks a cell wall
Explanation - Fastidious organisms need particular vitamins or amino acids not present in minimal media.
Correct answer is: Requires specific growth factors or vitamins
Q.94 Which of the following is NOT a typical requirement for bacterial growth?
Carbon source
Oxygen
Water
Nitrogen source
Explanation - While some bacteria require oxygen, many are anaerobes and do not need it.
Correct answer is: Oxygen
Q.95 Which of the following is a typical indicator used to detect pH changes in bacterial culture?
Phenol red
Methylene blue
Xanthine
Osmotic pressure
Explanation - Phenol red changes color with pH, indicating acid or base production by bacteria.
Correct answer is: Phenol red
Q.96 Which of the following best describes a 'non‑spore‑forming' bacterium?
It does not produce spores under stress
It can only grow in anaerobic conditions
It requires spores to initiate growth
It always forms spores
Explanation - Non-spore-formers lack the ability to form endospores during adverse conditions.
Correct answer is: It does not produce spores under stress
Q.97 Which of the following best explains why anaerobes often produce hydrogen sulfide (H₂S) in culture?
They use H₂S as an energy source
They reduce sulfite or thiosulfate to H₂S
They cannot metabolize sulfur
They generate oxygen
Explanation - Anaerobes can use sulfur compounds as electron acceptors, producing H₂S.
Correct answer is: They reduce sulfite or thiosulfate to H₂S
Q.98 Which of the following nutrients is essential for the synthesis of the bacterial cell wall peptidoglycan?
Calcium
Iron
Zinc
Magnesium
Explanation - Calcium ions stabilize the peptidoglycan layer and are involved in cell division.
Correct answer is: Calcium
Q.99 Which of the following best explains the role of 'trace elements' in bacterial media?
Serve as growth inhibitors
Provide structural support
Act as co‑enzymatic cofactors
Change pH
Explanation - Trace elements like iron and zinc are essential for enzyme function.
Correct answer is: Act as co‑enzymatic cofactors
Q.100 Which of the following is a key factor determining the optimal growth temperature for bacteria?
Humidity
Light intensity
Water activity
Enzyme kinetics
Explanation - Temperature affects enzyme activity, which in turn influences growth rates.
Correct answer is: Enzyme kinetics
Q.101 Which of the following best describes a 'chemoorganotroph'?
Obtains energy from light
Obtains both carbon and energy from organic compounds
Obtains energy from inorganic compounds
Obtains carbon from CO₂ and energy from light
Explanation - Chemoorganotrophs oxidize organic molecules for energy and carbon.
Correct answer is: Obtains both carbon and energy from organic compounds
Q.102 Which of the following indicates that a bacterium is a 'facultative anaerobe'?
It can grow only in the presence of oxygen
It can grow only in the absence of oxygen
It can grow with or without oxygen
It requires high temperature
Explanation - Facultative anaerobes switch metabolic pathways depending on oxygen availability.
Correct answer is: It can grow with or without oxygen
Q.103 Which of the following best describes the role of 'fermentation' in bacterial metabolism?
Production of ATP in presence of oxygen
Production of ATP without oxygen using organic substrates
Synthesis of DNA
Synthesis of fatty acids
Explanation - Fermentation allows anaerobic ATP production by metabolizing organic molecules.
Correct answer is: Production of ATP without oxygen using organic substrates
Q.104 Which of the following is a typical indicator used to detect pH changes in bacterial culture?
Phenol red
Methylene blue
Xanthine
Osmotic pressure
Explanation - Phenol red changes color with pH, indicating acid or base production by bacteria.
Correct answer is: Phenol red
Q.105 Which of the following best describes a 'chemoheterotroph'?
Obtains energy from light
Obtains both carbon and energy from organic compounds
Obtains energy from inorganic compounds
Obtains carbon from CO₂ and energy from light
Explanation - Chemoheterotrophs rely on organic molecules for both carbon and energy.
Correct answer is: Obtains both carbon and energy from organic compounds
Q.106 Which of the following is NOT a typical component of a bacterial culture media?
Carbon source
Energy source
Inhibitor
Growth factor
Explanation - Inhibitors are added to selective media but are not core components of general media.
Correct answer is: Inhibitor
Q.107 Which of the following best describes the term 'autolysis' in bacterial cell biology?
Cell division
Cell death due to self‑enzymatic degradation
Spore formation
Protein synthesis
Explanation - Autolysis occurs when bacterial enzymes break down the cell wall from within.
Correct answer is: Cell death due to self‑enzymatic degradation
Q.108 What does the abbreviation 'CFU' stand for in microbiology?
Carbon Fuel Unit
Colony Forming Unit
Cellular Fluorescent Unit
Control Factor Unit
Explanation - CFU is a measure of viable bacterial cells that can form colonies.
Correct answer is: Colony Forming Unit
Q.109 Which of the following media is best for detecting lactose fermentation?
MacConkey agar
Blood agar
Chocolate agar
Sabouraud agar
Explanation - MacConkey agar contains lactose and a pH indicator to distinguish lactose fermenters.
Correct answer is: MacConkey agar
Q.110 Which of the following is an example of a 'fast-growing' bacterium?
Escherichia coli
Mycobacterium tuberculosis
Streptococcus pyogenes
Listeria monocytogenes
Explanation - E. coli divides rapidly under favorable conditions, making it a model fast grower.
Correct answer is: Escherichia coli
Q.111 Which of the following best describes a 'chemoautotroph'?
Obtains energy from light and carbon from CO₂
Obtains energy from inorganic compounds and carbon from CO₂
Obtains energy from organic compounds and carbon from CO₂
Obtains energy from light and carbon from organic compounds
Explanation - Chemoautotrophs oxidize inorganic molecules for energy and fix CO₂ as carbon source.
Correct answer is: Obtains energy from inorganic compounds and carbon from CO₂
Q.112 Which of the following indicates that a bacterium is an obligate aerobe?
It can grow without oxygen
It requires oxygen for growth
It thrives at 4°C
It forms spores in air
Explanation - Obligate aerobes cannot grow without oxygen.
Correct answer is: It requires oxygen for growth
Q.113 Which of the following is a key requirement for bacterial DNA replication?
ATP
DNA polymerase
Glucose
Oxygen
Explanation - DNA polymerase synthesizes new DNA strands during replication.
Correct answer is: DNA polymerase