BIOD101 MODULE 3 EXAM PRACTICE | ESSENTIAL BIOLOGY I W/LAB (PORTAGE
LEARNING) | COMPREHENSIVE STUDY GUIDE & TESTBANK | PRACTICE QUESTIONS
& ANSWERS | LATEST UPDATE 2026/2027
TABLE OF CONTENTS
i. Metabolism and Biological Energy
ii. Catabolic and Anabolic Reactions
iii. Redox Reactions and Electron Carriers
iv. Glycolysis
v. Pyruvate Oxidation and the TCA Cycle
vi. Electron Transport Chain and Oxidative Phosphorylation
vii. Anaerobic Respiration and Fermentation
viii. Enzymatic Reactions and Enzyme Regulation
ix. Competitive and Noncompetitive Inhibition
x. Cellular Respiration Laboratory Applications
INTRODUCTION
This comprehensive BIOD101 Module 3 practice examination focuses on cellular
metabolism, energy transformation, enzymatic regulation, and cellular respiration. The
questions emphasize the mechanistic relationships among glycolysis, pyruvate
oxidation, the TCA cycle, electron transport, oxidative phosphorylation, and
fermentation. Students should be prepared to interpret metabolic scenarios, identify
consequences of pathway disruption, analyze enzyme behavior, and distinguish
catabolic from anabolic processes. The examination also incorporates experimental and
laboratory-style reasoning involving respiration and enzyme activity. The difficulty
ranges from advanced application to highly challenging analytical problems, requiring
more than memorization. Expect questions involving pathway integration, electron and
proton gradients, ATP production, metabolic regulation, inhibition, and interpretation
of altered cellular conditions.
Question 1
A researcher isolates mitochondria from a metabolically active eukaryotic cell and
supplies them with pyruvate, ADP, inorganic phosphate, oxygen, and the necessary
cofactors. Under normal conditions, which sequence most accurately describes the
major fate of pyruvate and the subsequent energy-transfer events?
,A. Pyruvate is converted directly into ATP, followed by fermentation in the
mitochondrial matrix.
B. Pyruvate is converted to acetyl-CoA, acetyl-CoA enters the TCA cycle, and reducing
equivalents subsequently donate electrons to the ETC.
C. Pyruvate enters the ETC directly and is oxidized to carbon dioxide by ATP synthase.
D. Pyruvate is converted to glucose before entering glycolysis within the mitochondrial
matrix.
🔴 Correct Answer: B. Pyruvate is converted to acetyl-CoA, acetyl-CoA enters the
TCA cycle, and reducing equivalents subsequently donate electrons to the ETC.
🔵 Explanation: Pyruvate oxidation produces acetyl-CoA, NADH, and CO₂. Acetyl-CoA
enters the TCA cycle, where additional NADH and FADH₂ are generated. These electron
carriers then transfer high-energy electrons to the electron transport chain, ultimately
supporting oxidative phosphorylation.
Question 2
A metabolic reaction requires an input of free energy and results in the formation of a
larger, more complex molecule from smaller molecular components. Which
classification best describes this reaction?
A. Catabolic and exergonic
B. Catabolic and oxidative
C. Anabolic and endergonic
D. Anabolic and hydrolytic
🔴 Correct Answer: C. Anabolic and endergonic
🔵 Explanation: Anabolic reactions synthesize complex molecules from simpler
components and generally require an energy input. They are therefore commonly
associated with endergonic reactions.
Question 3
During cellular respiration, NAD⁺ is converted to NADH. Which interpretation most
accurately describes this transformation?
A. NAD⁺ has been oxidized because it has accepted hydrogen ions.
B. NAD⁺ has been reduced because it has accepted high-energy electrons.
C. NADH has been reduced because it donated electrons to NAD⁺.
D. NADH has been oxidized because it gained electrons from glucose.
,🔴 Correct Answer: B. NAD⁺ has been reduced because it has accepted high-energy
electrons.
🔵 Explanation: Reduction involves the gain of electrons. NAD⁺ functions as an electron
carrier and becomes NADH after accepting electrons and associated hydrogen during
metabolic reactions. NADH can later donate those electrons to the ETC.
Question 4
A mutation substantially reduces the activity of phosphofructokinase in a cell. Which
immediate metabolic consequence would be most likely?
A. Increased conversion of fructose-6-phosphate into fructose-1,6-bisphosphate
B. Reduced flux through glycolysis beyond the phosphofructokinase-controlled step
C. Increased production of pyruvate from glucose
D. Increased direct transfer of electrons from glucose to oxygen
🔴 Correct Answer: B. Reduced flux through glycolysis beyond the
phosphofructokinase-controlled step
🔵 Explanation: Phosphofructokinase catalyzes the conversion of fructose-6-phosphate to
fructose-1,6-bisphosphate, an important regulatory step in glycolysis. Reduced enzyme
activity restricts downstream glycolytic flux and consequently decreases pyruvate
production from glucose.
Question 5
A cell is undergoing glycolysis under conditions in which oxygen is unavailable. Which
statement best explains why glycolysis can continue temporarily despite the absence of
oxygen?
A. Oxygen is not required for ATP production by substrate-level phosphorylation during
glycolysis.
B. Oxygen is replaced by ATP as the terminal electron acceptor.
C. The TCA cycle converts NADH back into NAD⁺ without oxygen.
D. The ETC produces oxygen as a byproduct that sustains glycolysis.
🔴 Correct Answer: A. Oxygen is not required for ATP production by substrate-level
phosphorylation during glycolysis.
🔵 Explanation: Glycolysis itself does not directly require molecular oxygen and produces
ATP through substrate-level phosphorylation. However, continued glycolysis under
, anaerobic conditions requires regeneration of NAD⁺, which fermentation can accomplish
by transferring electrons from NADH to organic molecules.
Question 6
A scientist adds a compound that binds to an enzyme's active site but does not
permanently modify the enzyme. Increasing the substrate concentration partially
restores the reaction rate. Which mechanism is most consistent with these
observations?
A. Noncompetitive inhibition
B. Competitive inhibition
C. Irreversible inhibition
D. Allosteric activation
🔴 Correct Answer: B. Competitive inhibition
🔵 Explanation: Competitive inhibitors compete with substrate for access to the enzyme's
active site. Increasing substrate concentration can reduce the inhibitor's relative effect
because substrate molecules have more opportunities to occupy the active site.
Question 7
A mutation prevents Complex IV of the mitochondrial electron transport chain from
transferring electrons to molecular oxygen. Which consequence would occur most
directly?
A. NADH and FADH₂ would be unable to efficiently donate electrons through the ETC,
causing upstream electron carriers to accumulate in reduced form.
B. Glycolysis would immediately stop because oxygen is a direct substrate of
phosphofructokinase.
C. ATP synthase would hydrolyze glucose directly to restore the proton gradient.
D. The TCA cycle would increase indefinitely because electron carriers would be
oxidized more rapidly.
🔴 Correct Answer: A. NADH and FADH₂ would be unable to efficiently donate
electrons through the ETC, causing upstream electron carriers to accumulate in
reduced form.
🔵 Explanation: Complex IV transfers electrons ultimately to oxygen, forming water.
Blocking this terminal electron-transfer step prevents continued electron flow through the
LEARNING) | COMPREHENSIVE STUDY GUIDE & TESTBANK | PRACTICE QUESTIONS
& ANSWERS | LATEST UPDATE 2026/2027
TABLE OF CONTENTS
i. Metabolism and Biological Energy
ii. Catabolic and Anabolic Reactions
iii. Redox Reactions and Electron Carriers
iv. Glycolysis
v. Pyruvate Oxidation and the TCA Cycle
vi. Electron Transport Chain and Oxidative Phosphorylation
vii. Anaerobic Respiration and Fermentation
viii. Enzymatic Reactions and Enzyme Regulation
ix. Competitive and Noncompetitive Inhibition
x. Cellular Respiration Laboratory Applications
INTRODUCTION
This comprehensive BIOD101 Module 3 practice examination focuses on cellular
metabolism, energy transformation, enzymatic regulation, and cellular respiration. The
questions emphasize the mechanistic relationships among glycolysis, pyruvate
oxidation, the TCA cycle, electron transport, oxidative phosphorylation, and
fermentation. Students should be prepared to interpret metabolic scenarios, identify
consequences of pathway disruption, analyze enzyme behavior, and distinguish
catabolic from anabolic processes. The examination also incorporates experimental and
laboratory-style reasoning involving respiration and enzyme activity. The difficulty
ranges from advanced application to highly challenging analytical problems, requiring
more than memorization. Expect questions involving pathway integration, electron and
proton gradients, ATP production, metabolic regulation, inhibition, and interpretation
of altered cellular conditions.
Question 1
A researcher isolates mitochondria from a metabolically active eukaryotic cell and
supplies them with pyruvate, ADP, inorganic phosphate, oxygen, and the necessary
cofactors. Under normal conditions, which sequence most accurately describes the
major fate of pyruvate and the subsequent energy-transfer events?
,A. Pyruvate is converted directly into ATP, followed by fermentation in the
mitochondrial matrix.
B. Pyruvate is converted to acetyl-CoA, acetyl-CoA enters the TCA cycle, and reducing
equivalents subsequently donate electrons to the ETC.
C. Pyruvate enters the ETC directly and is oxidized to carbon dioxide by ATP synthase.
D. Pyruvate is converted to glucose before entering glycolysis within the mitochondrial
matrix.
🔴 Correct Answer: B. Pyruvate is converted to acetyl-CoA, acetyl-CoA enters the
TCA cycle, and reducing equivalents subsequently donate electrons to the ETC.
🔵 Explanation: Pyruvate oxidation produces acetyl-CoA, NADH, and CO₂. Acetyl-CoA
enters the TCA cycle, where additional NADH and FADH₂ are generated. These electron
carriers then transfer high-energy electrons to the electron transport chain, ultimately
supporting oxidative phosphorylation.
Question 2
A metabolic reaction requires an input of free energy and results in the formation of a
larger, more complex molecule from smaller molecular components. Which
classification best describes this reaction?
A. Catabolic and exergonic
B. Catabolic and oxidative
C. Anabolic and endergonic
D. Anabolic and hydrolytic
🔴 Correct Answer: C. Anabolic and endergonic
🔵 Explanation: Anabolic reactions synthesize complex molecules from simpler
components and generally require an energy input. They are therefore commonly
associated with endergonic reactions.
Question 3
During cellular respiration, NAD⁺ is converted to NADH. Which interpretation most
accurately describes this transformation?
A. NAD⁺ has been oxidized because it has accepted hydrogen ions.
B. NAD⁺ has been reduced because it has accepted high-energy electrons.
C. NADH has been reduced because it donated electrons to NAD⁺.
D. NADH has been oxidized because it gained electrons from glucose.
,🔴 Correct Answer: B. NAD⁺ has been reduced because it has accepted high-energy
electrons.
🔵 Explanation: Reduction involves the gain of electrons. NAD⁺ functions as an electron
carrier and becomes NADH after accepting electrons and associated hydrogen during
metabolic reactions. NADH can later donate those electrons to the ETC.
Question 4
A mutation substantially reduces the activity of phosphofructokinase in a cell. Which
immediate metabolic consequence would be most likely?
A. Increased conversion of fructose-6-phosphate into fructose-1,6-bisphosphate
B. Reduced flux through glycolysis beyond the phosphofructokinase-controlled step
C. Increased production of pyruvate from glucose
D. Increased direct transfer of electrons from glucose to oxygen
🔴 Correct Answer: B. Reduced flux through glycolysis beyond the
phosphofructokinase-controlled step
🔵 Explanation: Phosphofructokinase catalyzes the conversion of fructose-6-phosphate to
fructose-1,6-bisphosphate, an important regulatory step in glycolysis. Reduced enzyme
activity restricts downstream glycolytic flux and consequently decreases pyruvate
production from glucose.
Question 5
A cell is undergoing glycolysis under conditions in which oxygen is unavailable. Which
statement best explains why glycolysis can continue temporarily despite the absence of
oxygen?
A. Oxygen is not required for ATP production by substrate-level phosphorylation during
glycolysis.
B. Oxygen is replaced by ATP as the terminal electron acceptor.
C. The TCA cycle converts NADH back into NAD⁺ without oxygen.
D. The ETC produces oxygen as a byproduct that sustains glycolysis.
🔴 Correct Answer: A. Oxygen is not required for ATP production by substrate-level
phosphorylation during glycolysis.
🔵 Explanation: Glycolysis itself does not directly require molecular oxygen and produces
ATP through substrate-level phosphorylation. However, continued glycolysis under
, anaerobic conditions requires regeneration of NAD⁺, which fermentation can accomplish
by transferring electrons from NADH to organic molecules.
Question 6
A scientist adds a compound that binds to an enzyme's active site but does not
permanently modify the enzyme. Increasing the substrate concentration partially
restores the reaction rate. Which mechanism is most consistent with these
observations?
A. Noncompetitive inhibition
B. Competitive inhibition
C. Irreversible inhibition
D. Allosteric activation
🔴 Correct Answer: B. Competitive inhibition
🔵 Explanation: Competitive inhibitors compete with substrate for access to the enzyme's
active site. Increasing substrate concentration can reduce the inhibitor's relative effect
because substrate molecules have more opportunities to occupy the active site.
Question 7
A mutation prevents Complex IV of the mitochondrial electron transport chain from
transferring electrons to molecular oxygen. Which consequence would occur most
directly?
A. NADH and FADH₂ would be unable to efficiently donate electrons through the ETC,
causing upstream electron carriers to accumulate in reduced form.
B. Glycolysis would immediately stop because oxygen is a direct substrate of
phosphofructokinase.
C. ATP synthase would hydrolyze glucose directly to restore the proton gradient.
D. The TCA cycle would increase indefinitely because electron carriers would be
oxidized more rapidly.
🔴 Correct Answer: A. NADH and FADH₂ would be unable to efficiently donate
electrons through the ETC, causing upstream electron carriers to accumulate in
reduced form.
🔵 Explanation: Complex IV transfers electrons ultimately to oxygen, forming water.
Blocking this terminal electron-transfer step prevents continued electron flow through the
