BIOD 171 Microbiology Module 3 Exam Questions
with Correct Answers and Expert Explanation for
Each Question
1. What is the primary function of an enzyme in a microbial metabolic pathway?
A. To increase the activation energy required for a reaction.
B. To act as a permanent reactant that is consumed in the process.
C. To lower the activation energy and speed up the reaction rate.
D. To provide the primary source of carbon for the cell.
Correct Answer: C
Expert Explanation: Enzymes serve as biological catalysts that significantly
accelerate the rate of chemical reactions within a cell. They function by lowering the
activation energy barrier, allowing reactions to occur more readily at physiological
temperatures. The enzyme remains unchanged throughout the process and can be
reused for subsequent reactions. Substrates bind specifically to the active site,
forming a temporary enzyme-substrate complex. This mechanism is essential for
sustaining the complex metabolic demands of microbial life.
2. Which of the following describes a catabolic process?
A. The synthesis of complex proteins from amino acids.
B. The replication of DNA during the S phase of growth.
,C. The breakdown of glucose into smaller molecules to release energy.
D. The assembly of phospholipids into the cell membrane.
Correct Answer: C
Expert Explanation: Catabolism involves the breakdown of complex organic
molecules into simpler ones, usually accompanied by the release of energy. This
energy is often captured in the form of ATP to be used by the cell later. In contrast,
anabolism refers to the energy-consuming process of building complex structures.
The breakdown of glucose during glycolysis is a classic example of a catabolic
pathway. These pathways provide the precursors and energy necessary for all
cellular functions.
3. How many net ATP molecules are produced during the process of glycolysis from
one molecule of glucose?
A. 38 ATP
B. 4 ATP
C. 2 ATP
D. 34 ATP
Correct Answer: C
,Expert Explanation: Glycolysis begins with an energy investment phase where two
ATP molecules are consumed to prime glucose. During the payoff phase, four ATP
molecules are generated through substrate-level phosphorylation. Therefore, the
net gain for the cell is exactly two ATP molecules per glucose molecule. In addition
to ATP, two molecules of NADH and two molecules of pyruvate are produced. This
process occurs in the cytosol of both prokaryotic and eukaryotic cells.
4. In aerobic respiration, what is the final electron acceptor in the Electron Transport
Chain?
A. Nitrate
B. Sulfate
C. Oxygen
D. Pyruvate
Correct Answer: C
Expert Explanation: The Electron Transport Chain is the final stage of aerobic
respiration where most ATP is generated. Electrons are passed through a series of
membrane-bound carriers, losing energy at each step. This energy is used to pump
protons across the membrane, creating a gradient. At the very end of the chain,
electrons are transferred to molecular oxygen. Oxygen then combines with protons
to form water as a harmless byproduct.
, 5. A microbe that thrives at temperatures between 20°C and 45°C is classified as a:
A. Psychrophile
B. Hyperthermophile
C. Thermophile
D. Mesophile
Correct Answer: D
Expert Explanation: Mesophiles are organisms that grow best at moderate
temperatures, typically ranging from 20°C to 45°C. This group includes most human
pathogens, as human body temperature is approximately 37°C. Psychrophiles prefer
much colder environments, while thermophiles require high heat to grow.
Temperature affects the stability of proteins and the fluidity of cell membranes.
Classification by temperature helps scientists understand where specific microbes
can survive and replicate.
6. During which phase of the microbial growth curve is the rate of cell division equal to
the rate of cell death?
A. Lag phase
B. Stationary phase
C. Log phase
with Correct Answers and Expert Explanation for
Each Question
1. What is the primary function of an enzyme in a microbial metabolic pathway?
A. To increase the activation energy required for a reaction.
B. To act as a permanent reactant that is consumed in the process.
C. To lower the activation energy and speed up the reaction rate.
D. To provide the primary source of carbon for the cell.
Correct Answer: C
Expert Explanation: Enzymes serve as biological catalysts that significantly
accelerate the rate of chemical reactions within a cell. They function by lowering the
activation energy barrier, allowing reactions to occur more readily at physiological
temperatures. The enzyme remains unchanged throughout the process and can be
reused for subsequent reactions. Substrates bind specifically to the active site,
forming a temporary enzyme-substrate complex. This mechanism is essential for
sustaining the complex metabolic demands of microbial life.
2. Which of the following describes a catabolic process?
A. The synthesis of complex proteins from amino acids.
B. The replication of DNA during the S phase of growth.
,C. The breakdown of glucose into smaller molecules to release energy.
D. The assembly of phospholipids into the cell membrane.
Correct Answer: C
Expert Explanation: Catabolism involves the breakdown of complex organic
molecules into simpler ones, usually accompanied by the release of energy. This
energy is often captured in the form of ATP to be used by the cell later. In contrast,
anabolism refers to the energy-consuming process of building complex structures.
The breakdown of glucose during glycolysis is a classic example of a catabolic
pathway. These pathways provide the precursors and energy necessary for all
cellular functions.
3. How many net ATP molecules are produced during the process of glycolysis from
one molecule of glucose?
A. 38 ATP
B. 4 ATP
C. 2 ATP
D. 34 ATP
Correct Answer: C
,Expert Explanation: Glycolysis begins with an energy investment phase where two
ATP molecules are consumed to prime glucose. During the payoff phase, four ATP
molecules are generated through substrate-level phosphorylation. Therefore, the
net gain for the cell is exactly two ATP molecules per glucose molecule. In addition
to ATP, two molecules of NADH and two molecules of pyruvate are produced. This
process occurs in the cytosol of both prokaryotic and eukaryotic cells.
4. In aerobic respiration, what is the final electron acceptor in the Electron Transport
Chain?
A. Nitrate
B. Sulfate
C. Oxygen
D. Pyruvate
Correct Answer: C
Expert Explanation: The Electron Transport Chain is the final stage of aerobic
respiration where most ATP is generated. Electrons are passed through a series of
membrane-bound carriers, losing energy at each step. This energy is used to pump
protons across the membrane, creating a gradient. At the very end of the chain,
electrons are transferred to molecular oxygen. Oxygen then combines with protons
to form water as a harmless byproduct.
, 5. A microbe that thrives at temperatures between 20°C and 45°C is classified as a:
A. Psychrophile
B. Hyperthermophile
C. Thermophile
D. Mesophile
Correct Answer: D
Expert Explanation: Mesophiles are organisms that grow best at moderate
temperatures, typically ranging from 20°C to 45°C. This group includes most human
pathogens, as human body temperature is approximately 37°C. Psychrophiles prefer
much colder environments, while thermophiles require high heat to grow.
Temperature affects the stability of proteins and the fluidity of cell membranes.
Classification by temperature helps scientists understand where specific microbes
can survive and replicate.
6. During which phase of the microbial growth curve is the rate of cell division equal to
the rate of cell death?
A. Lag phase
B. Stationary phase
C. Log phase
