Q.1 Which phase of bacterial growth is characterized by active cell division?
Lag phase
Log phase
Stationary phase
Death phase
Explanation - During the log (exponential) phase, bacteria divide rapidly at a constant rate, leading to exponential population growth.
Correct answer is: Log phase
Q.2 Which of the following is an essential macronutrient for microbial growth?
Calcium
Phosphorus
Zinc
Cobalt
Explanation - Phosphorus is a major macronutrient required for nucleic acids, ATP, and membrane phospholipids.
Correct answer is: Phosphorus
Q.3 The term ‘generation time’ refers to:
Time required for DNA replication
Time required for protein synthesis
Time required for cell to divide
Time required for spore germination
Explanation - Generation time is the interval required for a microbial population to double in number.
Correct answer is: Time required for cell to divide
Q.4 Which of the following media is both selective and differential?
Nutrient agar
MacConkey agar
Blood agar
Peptone water
Explanation - MacConkey agar is selective for Gram-negative bacteria and differential for lactose fermenters.
Correct answer is: MacConkey agar
Q.5 Facultative anaerobes:
Grow only in presence of oxygen
Grow only in absence of oxygen
Grow with or without oxygen
Cannot tolerate oxygen
Explanation - Facultative anaerobes can use oxygen for growth but can also survive in its absence.
Correct answer is: Grow with or without oxygen
Q.6 Which element is the most abundant in bacterial cells?
Carbon
Nitrogen
Oxygen
Hydrogen
Explanation - Carbon is the most abundant element in microbial cells, forming the backbone of organic molecules.
Correct answer is: Carbon
Q.7 Which type of bacteria require high salt concentrations for growth?
Halophiles
Thermophiles
Psychrophiles
Acidophiles
Explanation - Halophiles thrive in environments with high salt concentrations, such as salt lakes.
Correct answer is: Halophiles
Q.8 The stationary phase in bacterial growth occurs due to:
Nutrient depletion
Cell wall synthesis
Excess oxygen
Low temperature
Explanation - During the stationary phase, growth slows because nutrients are depleted and waste products accumulate.
Correct answer is: Nutrient depletion
Q.9 Which type of medium contains complex nutrients like yeast extract?
Defined medium
Synthetic medium
Complex medium
Minimal medium
Explanation - Complex media contain extracts and digests of natural products like yeast, peptone, or beef extract.
Correct answer is: Complex medium
Q.10 Obligate anaerobes are killed by oxygen because:
They lack ATP synthase
They lack catalase and superoxide dismutase
They lack ribosomes
They lack DNA polymerase
Explanation - Obligate anaerobes cannot detoxify harmful oxygen radicals due to absence of enzymes like catalase and SOD.
Correct answer is: They lack catalase and superoxide dismutase
Q.11 Which growth pattern is typically measured using a spectrophotometer?
Cell morphology
Turbidity
Colony size
DNA content
Explanation - Turbidity measurement estimates bacterial cell density in a culture by optical density readings.
Correct answer is: Turbidity
Q.12 Psychrophiles prefer which temperature range?
-20 to 10°C
0 to 20°C
20 to 45°C
45 to 80°C
Explanation - Psychrophiles grow optimally at low temperatures, typically below 20°C.
Correct answer is: 0 to 20°C
Q.13 Which of the following is an essential trace element for microbial enzymes?
Iron
Carbon
Sulfur
Oxygen
Explanation - Iron acts as a cofactor for many microbial enzymes, especially in electron transport systems.
Correct answer is: Iron
Q.14 Which type of culture medium is used to grow anaerobic bacteria?
Nutrient broth
Thioglycolate broth
MacConkey agar
Sabouraud agar
Explanation - Thioglycolate broth contains reducing agents to remove oxygen, supporting anaerobic bacterial growth.
Correct answer is: Thioglycolate broth
Q.15 Chemostat is used for:
Batch culture
Continuous culture
Solid culture
Enrichment culture
Explanation - Chemostats allow continuous culture by maintaining constant nutrient supply and waste removal.
Correct answer is: Continuous culture
Q.16 Which of the following is a chemically defined medium?
MacConkey agar
Nutrient agar
Minimal medium
Blood agar
Explanation - Minimal medium has precisely defined chemical composition, unlike complex media.
Correct answer is: Minimal medium
Q.17 Which pH range is optimal for neutrophiles?
pH 2-5
pH 6-8
pH 9-11
pH 12-14
Explanation - Neutrophiles grow best in near-neutral pH environments, around 6-8.
Correct answer is: pH 6-8
Q.18 Which bacterial growth phase is most suitable for antibiotic sensitivity testing?
Lag phase
Log phase
Stationary phase
Death phase
Explanation - During log phase, bacteria are metabolically active, making them more susceptible to antibiotics.
Correct answer is: Log phase
Q.19 Barophiles are microorganisms that grow optimally under:
Low pH
High salt concentration
High hydrostatic pressure
High temperature
Explanation - Barophiles thrive under extreme hydrostatic pressure, such as deep-sea environments.
Correct answer is: High hydrostatic pressure
Q.20 The death phase in bacterial growth is characterized by:
Rapid multiplication
Metabolic inactivity
Cell lysis
Increased sporulation
Explanation - In the death phase, cell death exceeds growth due to nutrient exhaustion and toxic waste accumulation.
Correct answer is: Cell lysis
Q.21 Which type of microorganism obtains energy from light and carbon from CO2?
Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
Explanation - Photoautotrophs, such as cyanobacteria, use light as an energy source and CO2 as a carbon source.
Correct answer is: Photoautotrophs
Q.22 Which growth measurement technique counts only viable cells?
Microscopic count
Spectrophotometry
Plate count method
Coulter counter
Explanation - The plate count method measures colony-forming units, representing only viable cells.
Correct answer is: Plate count method
Q.23 Microaerophiles require:
No oxygen
High oxygen
Reduced oxygen
Only carbon dioxide
Explanation - Microaerophiles need oxygen at lower levels than atmospheric concentration.
Correct answer is: Reduced oxygen
Q.24 Siderophores help bacteria acquire which nutrient?
Calcium
Phosphorus
Iron
Magnesium
Explanation - Siderophores are molecules secreted by bacteria to scavenge iron from the environment.
Correct answer is: Iron
Q.25 Which type of culture medium favors the growth of one type of microbe while inhibiting others?
Differential medium
Selective medium
Transport medium
Enrichment medium
Explanation - Selective media contain agents that suppress unwanted microbes and promote the growth of desired ones.
Correct answer is: Selective medium