BIO 250 Exam 2 V2 | BIO 250 Microbiology | Actual Q&A with
Rationale (BIO250 Exam 2) | StraighterLine
1. Which of the following best describes the role of a coenzyme in microbial metabolism?
A. It acts as the primary substrate for the enzyme’s catalytic site.
B. It provides the structural framework for the enzyme’s quaternary structure.
C. It functions as an organic molecule that assists enzymes by carrying functional groups or
electrons.
D. It serves as a competitive inhibitor to regulate metabolic pathways.
Correct Answer: C
Explanation: Coenzymes are small organic molecules, often derived from vitamins, that
are essential for the activity of certain enzymes. They facilitate reactions by transferring
chemical groups, atoms, or electrons between molecules. Without these specific cofactors,
the apoenzyme remains inactive and cannot catalyze the intended biochemical reaction.
2. During the process of glycolysis, what is the net gain of ATP molecules produced per
molecule of glucose via substrate-level phosphorylation?
A. 4 ATP
B. 1 ATP
C. 38 ATP
D. 2 ATP
Correct Answer: D
Explanation: Glycolysis involves an initial energy investment phase where 2 ATP
molecules are consumed to phosphorylate glucose. In the subsequent energy payoff phase,
4 ATP molecules are produced, resulting in a net gain of 2 ATP. This process occurs in the
cytoplasm and does not require oxygen to proceed.
3. A bacterial cell is placed in a hypertonic environment. What is the most likely physiological
outcome for the cell?
A. The cell will undergo plasmolysis as water leaves the cytoplasm.
B. The cell will maintain its shape due to the rigid peptidoglycan layer.
C. The cell will undergo osmotic lysis due to water influx.
D. The cell will increase its internal solute concentration to match the exterior.
Correct Answer: A
,Explanation: In a hypertonic solution, the concentration of solutes outside the cell is
higher than inside, causing water to move out of the cell by osmosis. This loss of water
causes the cytoplasmic membrane to shrink away from the cell wall, a process known as
plasmolysis. Plasmolysis generally inhibits bacterial growth and is the principle behind
using high salt or sugar concentrations for food preservation.
4. In DNA replication, which enzyme is responsible for relieving the torsional strain
(supercoiling) ahead of the replication fork?
A. DNA Polymerase I
B. Helicase
C. DNA Gyrase (Topoisomerase)
D. Primase
Correct Answer: C
Explanation: As helicase unwinds the DNA double helix, it creates tension and supercoiling
in the DNA strand ahead of the fork. DNA gyrase, a type of topoisomerase, introduces
breaks in the DNA to relax these coils and prevent the DNA from becoming too tightly
wound to be replicated. This enzyme is a frequent target for certain classes of antibiotics,
such as quinolones.
5. Select all the factors that can directly influence the activity of a bacterial enzyme: (Select all
that apply)
A. Temperature
B. pH level
C. Substrate concentration
D. Presence of inhibitors
E. Atmospheric nitrogen concentration
F. Salt concentration
Correct Answer: A, B, C, D, F
Explanation: Enzyme activity is highly sensitive to the physical and chemical environment
because the three-dimensional shape of the protein determines its function. Temperature
and pH can denature the enzyme, while substrate concentration affects the rate of reaction
until saturation is reached. Inhibitors can block the active site or change the enzyme’s
shape, and salt concentration affects the ionic bonds maintaining the protein structure.
6. Which metabolic pathway is common to both aerobic respiration and fermentation?
A. The Krebs Cycle
B. Glycolysis
, C. Electron Transport Chain
D. Chemiosmosis
Correct Answer: B
Explanation: Glycolysis is the initial step in the breakdown of glucose and does not require
oxygen, making it a universal pathway in many organisms. In aerobic respiration, glycolysis
is followed by the Krebs cycle and the ETC, whereas in fermentation, it is followed by the
reduction of pyruvate to regenerate NAD+. Thus, glycolysis serves as the foundational
metabolic engine regardless of the terminal electron acceptor available.
7. The process by which a bacteriophage transfers DNA from one host cell to another is
known as:
A. Transduction
B. Transformation
C. Conjugation
D. Transposition
Correct Answer: A
Explanation: Transduction is a form of horizontal gene transfer mediated by viruses that
infect bacteria. During the viral assembly phase, fragments of the host bacterial DNA may
be accidentally packaged into a phage head. When this phage infects a new bacterial cell, it
injects the previous host’s DNA, potentially altering the recipient’s genotype.
8. What is the primary purpose of the fermentation process in microbes that lack an electron
transport chain?
A. To produce maximum amounts of ATP per glucose molecule.
B. To regenerate NAD+ from NADH so glycolysis can continue.
C. To generate oxygen for the cell’s survival.
D. To synthesize complex amino acids from pyruvate.
Correct Answer: B
Explanation: During glycolysis, NAD+ is reduced to NADH, and if it is not oxidized back to
NAD+, the cell will run out of this essential electron carrier. Fermentation uses pyruvate or
a derivative as an electron acceptor to oxidize NADH back into NAD+. This allows the cell to
continue producing a small amount of ATP through glycolysis even in the absence of
aerobic or anaerobic respiration.
9. Which of the following statements regarding the Lac operon is true?
A. It is an example of a repressible operon that is usually ‘on’.
Rationale (BIO250 Exam 2) | StraighterLine
1. Which of the following best describes the role of a coenzyme in microbial metabolism?
A. It acts as the primary substrate for the enzyme’s catalytic site.
B. It provides the structural framework for the enzyme’s quaternary structure.
C. It functions as an organic molecule that assists enzymes by carrying functional groups or
electrons.
D. It serves as a competitive inhibitor to regulate metabolic pathways.
Correct Answer: C
Explanation: Coenzymes are small organic molecules, often derived from vitamins, that
are essential for the activity of certain enzymes. They facilitate reactions by transferring
chemical groups, atoms, or electrons between molecules. Without these specific cofactors,
the apoenzyme remains inactive and cannot catalyze the intended biochemical reaction.
2. During the process of glycolysis, what is the net gain of ATP molecules produced per
molecule of glucose via substrate-level phosphorylation?
A. 4 ATP
B. 1 ATP
C. 38 ATP
D. 2 ATP
Correct Answer: D
Explanation: Glycolysis involves an initial energy investment phase where 2 ATP
molecules are consumed to phosphorylate glucose. In the subsequent energy payoff phase,
4 ATP molecules are produced, resulting in a net gain of 2 ATP. This process occurs in the
cytoplasm and does not require oxygen to proceed.
3. A bacterial cell is placed in a hypertonic environment. What is the most likely physiological
outcome for the cell?
A. The cell will undergo plasmolysis as water leaves the cytoplasm.
B. The cell will maintain its shape due to the rigid peptidoglycan layer.
C. The cell will undergo osmotic lysis due to water influx.
D. The cell will increase its internal solute concentration to match the exterior.
Correct Answer: A
,Explanation: In a hypertonic solution, the concentration of solutes outside the cell is
higher than inside, causing water to move out of the cell by osmosis. This loss of water
causes the cytoplasmic membrane to shrink away from the cell wall, a process known as
plasmolysis. Plasmolysis generally inhibits bacterial growth and is the principle behind
using high salt or sugar concentrations for food preservation.
4. In DNA replication, which enzyme is responsible for relieving the torsional strain
(supercoiling) ahead of the replication fork?
A. DNA Polymerase I
B. Helicase
C. DNA Gyrase (Topoisomerase)
D. Primase
Correct Answer: C
Explanation: As helicase unwinds the DNA double helix, it creates tension and supercoiling
in the DNA strand ahead of the fork. DNA gyrase, a type of topoisomerase, introduces
breaks in the DNA to relax these coils and prevent the DNA from becoming too tightly
wound to be replicated. This enzyme is a frequent target for certain classes of antibiotics,
such as quinolones.
5. Select all the factors that can directly influence the activity of a bacterial enzyme: (Select all
that apply)
A. Temperature
B. pH level
C. Substrate concentration
D. Presence of inhibitors
E. Atmospheric nitrogen concentration
F. Salt concentration
Correct Answer: A, B, C, D, F
Explanation: Enzyme activity is highly sensitive to the physical and chemical environment
because the three-dimensional shape of the protein determines its function. Temperature
and pH can denature the enzyme, while substrate concentration affects the rate of reaction
until saturation is reached. Inhibitors can block the active site or change the enzyme’s
shape, and salt concentration affects the ionic bonds maintaining the protein structure.
6. Which metabolic pathway is common to both aerobic respiration and fermentation?
A. The Krebs Cycle
B. Glycolysis
, C. Electron Transport Chain
D. Chemiosmosis
Correct Answer: B
Explanation: Glycolysis is the initial step in the breakdown of glucose and does not require
oxygen, making it a universal pathway in many organisms. In aerobic respiration, glycolysis
is followed by the Krebs cycle and the ETC, whereas in fermentation, it is followed by the
reduction of pyruvate to regenerate NAD+. Thus, glycolysis serves as the foundational
metabolic engine regardless of the terminal electron acceptor available.
7. The process by which a bacteriophage transfers DNA from one host cell to another is
known as:
A. Transduction
B. Transformation
C. Conjugation
D. Transposition
Correct Answer: A
Explanation: Transduction is a form of horizontal gene transfer mediated by viruses that
infect bacteria. During the viral assembly phase, fragments of the host bacterial DNA may
be accidentally packaged into a phage head. When this phage infects a new bacterial cell, it
injects the previous host’s DNA, potentially altering the recipient’s genotype.
8. What is the primary purpose of the fermentation process in microbes that lack an electron
transport chain?
A. To produce maximum amounts of ATP per glucose molecule.
B. To regenerate NAD+ from NADH so glycolysis can continue.
C. To generate oxygen for the cell’s survival.
D. To synthesize complex amino acids from pyruvate.
Correct Answer: B
Explanation: During glycolysis, NAD+ is reduced to NADH, and if it is not oxidized back to
NAD+, the cell will run out of this essential electron carrier. Fermentation uses pyruvate or
a derivative as an electron acceptor to oxidize NADH back into NAD+. This allows the cell to
continue producing a small amount of ATP through glycolysis even in the absence of
aerobic or anaerobic respiration.
9. Which of the following statements regarding the Lac operon is true?
A. It is an example of a repressible operon that is usually ‘on’.
