MICROBIOLOGY · OBJECTIVE ASSESSMENT
A+ VERIFIED
Microbiology BIOD 171 Module 3 Exam
Portage learning/Geneva College/ABC nursing, 2026/2027
Actual Questions with Revised Answers, 100% Verified. — Complete
Official Exam
A+ Verified Full Rationales Verified Answers
A+ 5 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage Core exam domains Every answer explained
WHAT THIS COVERS
01 Microbial Metabolism and Energy Production
02 Microbial Growth and Environmental Influences
03 Physical Methods of Microbial Control
04 Chemical Control and Disinfection
05 Antimicrobial Drugs and Resistance Mechanisms
ABOUT THIS ASSESSMENT
Build mastery in microbiology module 3 — from microbial metabolism and energy
pathways to growth requirements, physical and chemical control of microbes,
disinfection, sterilization, and the mechanisms of antimicrobial drugs and resistance.
This original study bank targets application and analysis skills for BIOD 171
Module 3, with full rationales for every answer. For review use only; not an
institutional proctored assessment.
PASSING SCORE LEVEL FORMAT
80% Advanced (Portage Learning Module Exam) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Microbial Metabolism and Energy Production
Q1. A laboratory culture of Escherichia coli is grown under strictly anaerobic conditions with glucose as the sole carbon source.
The organism produces mixed acids and gas. Which metabolic pathway is primarily responsible for regenerating NAD+
under these conditions?
A. Oxidative phosphorylation via the electron transport chain
B. The complete tricarboxylic acid cycle with oxygen as terminal acceptor
C. Fermentation pathways that reduce pyruvate or its derivatives
D. Photosynthetic photophosphorylation
Correct Answer: C
Rationale:
Under anaerobic conditions E. coli cannot use an electron transport chain with oxygen. Fermentation pathways reoxidize NADH by
transferring electrons to organic intermediates derived from pyruvate, allowing glycolysis to continue. Oxidative phosphorylation and a full
TCA cycle require aerobic respiration.
Q2. A researcher measures a high P/O ratio in a preparation of bacterial membrane vesicles oxidizing NADH. What does this
experimental result indicate about energy conservation?
A. Substrate-level phosphorylation is the sole source of ATP
B. The organism is exclusively fermentative
C. Electron transport is tightly coupled to ATP synthesis via a proton motive force
D. ATP is being hydrolyzed rather than synthesized
Correct Answer: C
Rationale:
A high P/O ratio reflects efficient coupling of electron transport to ATP formation through the proton gradient and ATP synthase.
Substrate-level phosphorylation alone would not produce a measurable P/O ratio linked to NADH oxidation.
Q3. An obligate aerobe is shifted from a glucose-rich medium to a medium containing only fatty acids. Which metabolic
adaptation is most essential for continued ATP generation?
A. Induction of beta-oxidation and the glyoxylate cycle or TCA cycle enzymes
B. Increased reliance on the Embden-Meyerhof-Parnas pathway alone
C. Complete shutdown of the electron transport chain
D. Exclusive use of lactic acid fermentation
Correct Answer: A
Rationale:
Fatty acids are catabolized by beta-oxidation to acetyl-CoA, which enters the TCA cycle (or glyoxylate cycle in some microbes). An
obligate aerobe continues to use oxidative phosphorylation; fermentation is not its primary strategy.
Q4. A mutant bacterial strain is unable to synthesize heme and therefore lacks functional cytochromes. Growth yields on glucose
are dramatically reduced even though the cells remain viable under aerobic conditions. What is the most likely explanation?
A. Glycolysis has been completely blocked
B. The organism can still perform substrate-level phosphorylation but cannot carry out oxidative phosphorylation
C. The pentose-phosphate pathway is inactivated
D. All ATP synthesis has ceased
Correct Answer: B
Rationale:
Absence of cytochromes abolishes electron transport and oxidative phosphorylation. Substrate-level phosphorylation in glycolysis and the
TCA cycle can still generate limited ATP, allowing slow growth but much lower yields.
Q5. During the transition from lag to log phase in a batch culture of Bacillus subtilis, the cells increase the synthesis of enzymes
of the TCA cycle and electron transport chain. This change is primarily a response to which environmental cue?
A. Sudden decrease in external pH
B. Depletion of all nitrogen sources
C. Accumulation of toxic fermentation products only
D. Increasing availability of oxygen and the need for efficient energy generation as cell density rises
Correct Answer: D
Rationale:
As cells enter active growth they optimize energy efficiency. Induction of respiratory enzymes allows higher ATP yields from glucose when
oxygen is available, supporting rapid biomass increase.
STUVIA ACTUAL EXAM · Page 2
, SECTION 1: Microbial Metabolism and Energy Production
Q5. During the transition from lag to log phase in a batch culture of Bacillus subtilis, the cells increase the synthesis of enzymes
of the TCA cycle and electron transport chain. This change is primarily a response to which environmental cue?
A. Sudden decrease in external pH
B. Depletion of all nitrogen sources
C. Accumulation of toxic fermentation products only
D. Increasing availability of oxygen and the need for efficient energy generation as cell density rises
Correct Answer: D
Rationale:
As cells enter active growth they optimize energy efficiency. Induction of respiratory enzymes allows higher ATP yields from glucose when
oxygen is available, supporting rapid biomass increase.
Q6. A microbiologist observes that a culture of lactic acid bacteria produces large amounts of lactate from glucose yet generates
only a net of 2 ATP per glucose. Why is the ATP yield so low compared with aerobic respiration?
A. Electrons from NADH are used to reduce pyruvate rather than being passed through an electron transport chain, so oxidative
phosphorylation does not occur
B. The bacteria lack any kinases
C. Glucose is never phosphorylated
D. The Embden-Meyerhof pathway is absent
Correct Answer: A
Rationale:
In homolactic fermentation the 2 ATP net from glycolysis are the only ATP formed; NADH is reoxidized by lactate dehydrogenase. No
proton motive force is generated for additional ATP synthesis.
Q7. An organism oxidizes hydrogen gas and fixes CO2 into organic carbon using the Calvin cycle while deriving energy from the
oxidation of H2. How is this lifestyle classified?
A. Photoheterotrophy
B. Photoautotrophy using water as electron donor
C. Chemoautotrophy (chemolithoautotrophy)
D. Fermentative heterotrophy
Correct Answer: C
Rationale:
Energy is obtained from chemical oxidation of an inorganic electron donor (H2) and carbon is obtained from CO2; this defines
chemolithoautotrophy.
Q8. A student claims that the Embden-Meyerhof-Parnas pathway and the Entner-Doudoroff pathway produce identical ATP
yields from glucose under anaerobic conditions. Which statement corrects this claim?
A. Both pathways always yield 4 net ATP
B. The Entner-Doudoroff pathway never functions anaerobically
C. The Entner-Doudoroff pathway yields only 1 net ATP per glucose while EMP yields 2 net ATP
D. EMP cannot operate without oxygen
Correct Answer: C
Rationale:
EMP glycolysis nets 2 ATP. The Entner-Doudoroff pathway nets only 1 ATP because it produces only one glyceraldehyde-3-phosphate
that continues through the payoff phase.
Q9. In an experiment, addition of an uncoupler of oxidative phosphorylation to aerobically respiring bacteria causes oxygen
consumption to continue or even increase while ATP levels fall. What does this observation demonstrate?
A. Electron transport requires ATP hydrolysis
B. Electron transport and ATP synthesis are normally coupled; uncoupling allows electron flow without ATP formation
C. The cells have switched to fermentation
D. Oxygen is no longer the terminal electron acceptor
Correct Answer: B
Rationale:
Uncouplers dissipate the proton gradient so that electron transport proceeds without ATP synthase activity. Respiration continues (or
accelerates) while ATP synthesis declines.
STUVIA ACTUAL EXAM · Page 3
, SECTION 1: Microbial Metabolism and Energy Production
Q9. In an experiment, addition of an uncoupler of oxidative phosphorylation to aerobically respiring bacteria causes oxygen
consumption to continue or even increase while ATP levels fall. What does this observation demonstrate?
A. Electron transport requires ATP hydrolysis
B. Electron transport and ATP synthesis are normally coupled; uncoupling allows electron flow without ATP formation
C. The cells have switched to fermentation
D. Oxygen is no longer the terminal electron acceptor
Correct Answer: B
Rationale:
Uncouplers dissipate the proton gradient so that electron transport proceeds without ATP synthase activity. Respiration continues (or
accelerates) while ATP synthesis declines.
Q10. A thermophilic bacterium grows optimally at 75 °C and uses elemental sulfur as a terminal electron acceptor. Which
metabolic category best describes this organism?
A. Aerobic chemoheterotroph
B. Oxygenic phototroph
C. Anaerobic chemolithotroph or chemoorganotroph capable of sulfur respiration
D. Obligate fermenter that cannot perform anaerobic respiration
Correct Answer: C
Rationale:
Use of an inorganic electron acceptor other than oxygen constitutes anaerobic respiration. Many thermophiles that reduce sulfur obtain
energy this way.
Q11. During glycolysis a bacterial cell generates reduced electron carriers. If the cell is performing aerobic respiration, where do
the electrons ultimately go and what is produced?
A. Electrons reduce pyruvate to lactate; no additional ATP is formed
B. Electrons are passed through membrane carriers to O2, generating a proton motive force that drives ATP synthesis
C. Electrons are discarded as H2 gas only
D. Electrons remain bound to NAD+ indefinitely
Correct Answer: B
Rationale:
In aerobic respiration NADH and FADH2 donate electrons to the electron transport chain; the terminal acceptor is oxygen, and the
resulting proton gradient powers ATP synthase.
Q12. A culture of purple non-sulfur bacteria is incubated anaerobically in the light with malate as carbon source. No O2 is evolved.
Which process is occurring?
A. Anoxygenic photoheterotrophy
B. Oxygenic photosynthesis with water as electron donor
C. Chemolithoautotrophy
D. Aerobic respiration of malate
Correct Answer: A
Rationale:
Purple non-sulfur bacteria perform anoxygenic photosynthesis and can use organic compounds as carbon sources (photoheterotrophy).
They do not evolve oxygen.
Q13. An investigator finds that a particular bacterium generates ATP solely by substrate-level phosphorylation even when oxygen
is abundant. Which conclusion is most reasonable?
A. The organism must be a phototroph
B. Oxygen is toxic to all bacteria
C. The organism lacks a functional electron transport chain or is an obligate fermenter
D. Substrate-level phosphorylation requires oxygen
Correct Answer: C
Rationale:
If oxygen is available yet only substrate-level phosphorylation occurs, the cells either lack respiratory capability or are genetically
committed to fermentation.
STUVIA ACTUAL EXAM · Page 4
A+ VERIFIED
Microbiology BIOD 171 Module 3 Exam
Portage learning/Geneva College/ABC nursing, 2026/2027
Actual Questions with Revised Answers, 100% Verified. — Complete
Official Exam
A+ Verified Full Rationales Verified Answers
A+ 5 100%
QUESTIONS SECTIONS RATIONALES
Complete coverage Core exam domains Every answer explained
WHAT THIS COVERS
01 Microbial Metabolism and Energy Production
02 Microbial Growth and Environmental Influences
03 Physical Methods of Microbial Control
04 Chemical Control and Disinfection
05 Antimicrobial Drugs and Resistance Mechanisms
ABOUT THIS ASSESSMENT
Build mastery in microbiology module 3 — from microbial metabolism and energy
pathways to growth requirements, physical and chemical control of microbes,
disinfection, sterilization, and the mechanisms of antimicrobial drugs and resistance.
This original study bank targets application and analysis skills for BIOD 171
Module 3, with full rationales for every answer. For review use only; not an
institutional proctored assessment.
PASSING SCORE LEVEL FORMAT
80% Advanced (Portage Learning Module Exam) Application / Analysis
STUVIA ACTUAL EXAM Page 1
, SECTION 1: Microbial Metabolism and Energy Production
Q1. A laboratory culture of Escherichia coli is grown under strictly anaerobic conditions with glucose as the sole carbon source.
The organism produces mixed acids and gas. Which metabolic pathway is primarily responsible for regenerating NAD+
under these conditions?
A. Oxidative phosphorylation via the electron transport chain
B. The complete tricarboxylic acid cycle with oxygen as terminal acceptor
C. Fermentation pathways that reduce pyruvate or its derivatives
D. Photosynthetic photophosphorylation
Correct Answer: C
Rationale:
Under anaerobic conditions E. coli cannot use an electron transport chain with oxygen. Fermentation pathways reoxidize NADH by
transferring electrons to organic intermediates derived from pyruvate, allowing glycolysis to continue. Oxidative phosphorylation and a full
TCA cycle require aerobic respiration.
Q2. A researcher measures a high P/O ratio in a preparation of bacterial membrane vesicles oxidizing NADH. What does this
experimental result indicate about energy conservation?
A. Substrate-level phosphorylation is the sole source of ATP
B. The organism is exclusively fermentative
C. Electron transport is tightly coupled to ATP synthesis via a proton motive force
D. ATP is being hydrolyzed rather than synthesized
Correct Answer: C
Rationale:
A high P/O ratio reflects efficient coupling of electron transport to ATP formation through the proton gradient and ATP synthase.
Substrate-level phosphorylation alone would not produce a measurable P/O ratio linked to NADH oxidation.
Q3. An obligate aerobe is shifted from a glucose-rich medium to a medium containing only fatty acids. Which metabolic
adaptation is most essential for continued ATP generation?
A. Induction of beta-oxidation and the glyoxylate cycle or TCA cycle enzymes
B. Increased reliance on the Embden-Meyerhof-Parnas pathway alone
C. Complete shutdown of the electron transport chain
D. Exclusive use of lactic acid fermentation
Correct Answer: A
Rationale:
Fatty acids are catabolized by beta-oxidation to acetyl-CoA, which enters the TCA cycle (or glyoxylate cycle in some microbes). An
obligate aerobe continues to use oxidative phosphorylation; fermentation is not its primary strategy.
Q4. A mutant bacterial strain is unable to synthesize heme and therefore lacks functional cytochromes. Growth yields on glucose
are dramatically reduced even though the cells remain viable under aerobic conditions. What is the most likely explanation?
A. Glycolysis has been completely blocked
B. The organism can still perform substrate-level phosphorylation but cannot carry out oxidative phosphorylation
C. The pentose-phosphate pathway is inactivated
D. All ATP synthesis has ceased
Correct Answer: B
Rationale:
Absence of cytochromes abolishes electron transport and oxidative phosphorylation. Substrate-level phosphorylation in glycolysis and the
TCA cycle can still generate limited ATP, allowing slow growth but much lower yields.
Q5. During the transition from lag to log phase in a batch culture of Bacillus subtilis, the cells increase the synthesis of enzymes
of the TCA cycle and electron transport chain. This change is primarily a response to which environmental cue?
A. Sudden decrease in external pH
B. Depletion of all nitrogen sources
C. Accumulation of toxic fermentation products only
D. Increasing availability of oxygen and the need for efficient energy generation as cell density rises
Correct Answer: D
Rationale:
As cells enter active growth they optimize energy efficiency. Induction of respiratory enzymes allows higher ATP yields from glucose when
oxygen is available, supporting rapid biomass increase.
STUVIA ACTUAL EXAM · Page 2
, SECTION 1: Microbial Metabolism and Energy Production
Q5. During the transition from lag to log phase in a batch culture of Bacillus subtilis, the cells increase the synthesis of enzymes
of the TCA cycle and electron transport chain. This change is primarily a response to which environmental cue?
A. Sudden decrease in external pH
B. Depletion of all nitrogen sources
C. Accumulation of toxic fermentation products only
D. Increasing availability of oxygen and the need for efficient energy generation as cell density rises
Correct Answer: D
Rationale:
As cells enter active growth they optimize energy efficiency. Induction of respiratory enzymes allows higher ATP yields from glucose when
oxygen is available, supporting rapid biomass increase.
Q6. A microbiologist observes that a culture of lactic acid bacteria produces large amounts of lactate from glucose yet generates
only a net of 2 ATP per glucose. Why is the ATP yield so low compared with aerobic respiration?
A. Electrons from NADH are used to reduce pyruvate rather than being passed through an electron transport chain, so oxidative
phosphorylation does not occur
B. The bacteria lack any kinases
C. Glucose is never phosphorylated
D. The Embden-Meyerhof pathway is absent
Correct Answer: A
Rationale:
In homolactic fermentation the 2 ATP net from glycolysis are the only ATP formed; NADH is reoxidized by lactate dehydrogenase. No
proton motive force is generated for additional ATP synthesis.
Q7. An organism oxidizes hydrogen gas and fixes CO2 into organic carbon using the Calvin cycle while deriving energy from the
oxidation of H2. How is this lifestyle classified?
A. Photoheterotrophy
B. Photoautotrophy using water as electron donor
C. Chemoautotrophy (chemolithoautotrophy)
D. Fermentative heterotrophy
Correct Answer: C
Rationale:
Energy is obtained from chemical oxidation of an inorganic electron donor (H2) and carbon is obtained from CO2; this defines
chemolithoautotrophy.
Q8. A student claims that the Embden-Meyerhof-Parnas pathway and the Entner-Doudoroff pathway produce identical ATP
yields from glucose under anaerobic conditions. Which statement corrects this claim?
A. Both pathways always yield 4 net ATP
B. The Entner-Doudoroff pathway never functions anaerobically
C. The Entner-Doudoroff pathway yields only 1 net ATP per glucose while EMP yields 2 net ATP
D. EMP cannot operate without oxygen
Correct Answer: C
Rationale:
EMP glycolysis nets 2 ATP. The Entner-Doudoroff pathway nets only 1 ATP because it produces only one glyceraldehyde-3-phosphate
that continues through the payoff phase.
Q9. In an experiment, addition of an uncoupler of oxidative phosphorylation to aerobically respiring bacteria causes oxygen
consumption to continue or even increase while ATP levels fall. What does this observation demonstrate?
A. Electron transport requires ATP hydrolysis
B. Electron transport and ATP synthesis are normally coupled; uncoupling allows electron flow without ATP formation
C. The cells have switched to fermentation
D. Oxygen is no longer the terminal electron acceptor
Correct Answer: B
Rationale:
Uncouplers dissipate the proton gradient so that electron transport proceeds without ATP synthase activity. Respiration continues (or
accelerates) while ATP synthesis declines.
STUVIA ACTUAL EXAM · Page 3
, SECTION 1: Microbial Metabolism and Energy Production
Q9. In an experiment, addition of an uncoupler of oxidative phosphorylation to aerobically respiring bacteria causes oxygen
consumption to continue or even increase while ATP levels fall. What does this observation demonstrate?
A. Electron transport requires ATP hydrolysis
B. Electron transport and ATP synthesis are normally coupled; uncoupling allows electron flow without ATP formation
C. The cells have switched to fermentation
D. Oxygen is no longer the terminal electron acceptor
Correct Answer: B
Rationale:
Uncouplers dissipate the proton gradient so that electron transport proceeds without ATP synthase activity. Respiration continues (or
accelerates) while ATP synthesis declines.
Q10. A thermophilic bacterium grows optimally at 75 °C and uses elemental sulfur as a terminal electron acceptor. Which
metabolic category best describes this organism?
A. Aerobic chemoheterotroph
B. Oxygenic phototroph
C. Anaerobic chemolithotroph or chemoorganotroph capable of sulfur respiration
D. Obligate fermenter that cannot perform anaerobic respiration
Correct Answer: C
Rationale:
Use of an inorganic electron acceptor other than oxygen constitutes anaerobic respiration. Many thermophiles that reduce sulfur obtain
energy this way.
Q11. During glycolysis a bacterial cell generates reduced electron carriers. If the cell is performing aerobic respiration, where do
the electrons ultimately go and what is produced?
A. Electrons reduce pyruvate to lactate; no additional ATP is formed
B. Electrons are passed through membrane carriers to O2, generating a proton motive force that drives ATP synthesis
C. Electrons are discarded as H2 gas only
D. Electrons remain bound to NAD+ indefinitely
Correct Answer: B
Rationale:
In aerobic respiration NADH and FADH2 donate electrons to the electron transport chain; the terminal acceptor is oxygen, and the
resulting proton gradient powers ATP synthase.
Q12. A culture of purple non-sulfur bacteria is incubated anaerobically in the light with malate as carbon source. No O2 is evolved.
Which process is occurring?
A. Anoxygenic photoheterotrophy
B. Oxygenic photosynthesis with water as electron donor
C. Chemolithoautotrophy
D. Aerobic respiration of malate
Correct Answer: A
Rationale:
Purple non-sulfur bacteria perform anoxygenic photosynthesis and can use organic compounds as carbon sources (photoheterotrophy).
They do not evolve oxygen.
Q13. An investigator finds that a particular bacterium generates ATP solely by substrate-level phosphorylation even when oxygen
is abundant. Which conclusion is most reasonable?
A. The organism must be a phototroph
B. Oxygen is toxic to all bacteria
C. The organism lacks a functional electron transport chain or is an obligate fermenter
D. Substrate-level phosphorylation requires oxygen
Correct Answer: C
Rationale:
If oxygen is available yet only substrate-level phosphorylation occurs, the cells either lack respiratory capability or are genetically
committed to fermentation.
STUVIA ACTUAL EXAM · Page 4
