BIO 250 Exam 2 V3 | BIO 250 Microbiology | Actual Q&A with
Rationale (BIO250 Exam 2) | StraighterLine
1. Enzymes are biological catalysts that increase the rate of chemical reactions by doing which
of the following?
A. Increasing the activation energy required for a reaction
B. Changing the final equilibrium of the reaction
C. Lowering the activation energy required for a reaction
D. Being consumed in the process of the reaction
Correct Answer: C
Explanation: Enzymes function by lowering the activation energy barrier, allowing
reactions to occur more rapidly at physiological temperatures. They bind specifically to
substrates to stabilize the transition state without being permanently altered themselves.
This process does not change the overall free energy change or the equilibrium constant of
the reaction.
2. Which of the following environmental factors can influence the rate of enzyme-catalyzed
reactions? (Select all that apply)
A. Temperature
B. pH levels
C. Substrate concentration
D. Atmospheric nitrogen levels
E. Presence of inhibitors
F. Enzyme concentration
Correct Answer: A,B,C,E,F
Explanation: Enzyme activity is highly sensitive to the physical and chemical environment,
specifically temperature and pH which can denature the protein structure. Additionally, the
availability of substrates and the presence of competitive or non-competitive inhibitors
directly dictate the kinetic rate. Enzyme concentration is also a limiting factor in
determining the maximum velocity of a reaction.
3. During aerobic respiration, which molecule acts as the final electron acceptor in the
electron transport chain?
A. Nitrate
B. Sulfate
,C. Oxygen
D. Pyruvate
Correct Answer: C
Explanation: In aerobic respiration, molecular oxygen (O2) serves as the terminal electron
acceptor at the end of the electron transport chain. This reduction results in the formation
of water as a byproduct. Anaerobic respiration would utilize different inorganic molecules
like nitrate or sulfate as acceptors.
4. Which phase of the bacterial growth curve is characterized by a period of little to no cell
division as the population adapts to a new environment?
A. Log phase
B. Stationary phase
C. Lag phase
D. Death phase
Correct Answer: C
Explanation: The lag phase represents the initial period where cells are metabolically
active but not yet dividing. During this time, bacteria are synthesizing necessary enzymes
and proteins to utilize the available nutrients in the medium. The duration of this phase
varies depending on the species and the shift in environmental conditions.
5. In DNA replication, which enzyme is responsible for unwinding the double helix at the
replication fork?
A. DNA Polymerase III
B. Ligase
C. Primase
D. Helicase
Correct Answer: D
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the two DNA strands. This creates the replication fork where
other enzymes like DNA polymerase can begin synthesis. Single-strand binding proteins
then stabilize the unwound DNA to prevent it from re-annealing.
6. Which of the following are products of the Krebs cycle (Citric Acid Cycle) per one turn?
(Select all that apply)
A. 2 molecules of CO2
B. 3 molecules of NADH
, C. 1 molecule of FADH2
D. 1 molecule of ATP (or GTP)
E. 2 molecules of Pyruvate
Correct Answer: A,B,C,D
Explanation: The Krebs cycle processes one Acetyl-CoA per turn, releasing two CO2
molecules as waste. It also generates high-energy electron carriers in the form of three
NADH and one FADH2. A single molecule of ATP or GTP is produced through substrate-
level phosphorylation during the cycle.
7. A mutation that results in the insertion of a single nucleotide into a DNA sequence is most
likely to cause what type of effect?
A. Frameshift mutation
B. Missense mutation
C. Silent mutation
D. Nonsense mutation
Correct Answer: A
Explanation: An insertion or deletion of nucleotides not in multiples of three shifts the
reading frame of the mRNA codons. This frameshift usually leads to a completely different
amino acid sequence downstream and often creates a premature stop codon. Such
mutations are typically deleterious to the function of the resulting protein.
8. Which process involves the transfer of DNA from a donor to a recipient cell via a
bacteriophage?
A. Transformation
B. Conjugation
C. Translation
D. Transduction
Correct Answer: D
Explanation: Transduction is a mechanism of horizontal gene transfer where bacterial
DNA is packaged into a viral capsid by mistake during phage assembly. When this phage
infects a new host, it injects the bacterial DNA instead of viral DNA. This process allows for
genetic recombination between different bacterial cells.
9. What is the net gain of ATP molecules produced during glycolysis from a single molecule of
glucose?
A. 36 ATP
Rationale (BIO250 Exam 2) | StraighterLine
1. Enzymes are biological catalysts that increase the rate of chemical reactions by doing which
of the following?
A. Increasing the activation energy required for a reaction
B. Changing the final equilibrium of the reaction
C. Lowering the activation energy required for a reaction
D. Being consumed in the process of the reaction
Correct Answer: C
Explanation: Enzymes function by lowering the activation energy barrier, allowing
reactions to occur more rapidly at physiological temperatures. They bind specifically to
substrates to stabilize the transition state without being permanently altered themselves.
This process does not change the overall free energy change or the equilibrium constant of
the reaction.
2. Which of the following environmental factors can influence the rate of enzyme-catalyzed
reactions? (Select all that apply)
A. Temperature
B. pH levels
C. Substrate concentration
D. Atmospheric nitrogen levels
E. Presence of inhibitors
F. Enzyme concentration
Correct Answer: A,B,C,E,F
Explanation: Enzyme activity is highly sensitive to the physical and chemical environment,
specifically temperature and pH which can denature the protein structure. Additionally, the
availability of substrates and the presence of competitive or non-competitive inhibitors
directly dictate the kinetic rate. Enzyme concentration is also a limiting factor in
determining the maximum velocity of a reaction.
3. During aerobic respiration, which molecule acts as the final electron acceptor in the
electron transport chain?
A. Nitrate
B. Sulfate
,C. Oxygen
D. Pyruvate
Correct Answer: C
Explanation: In aerobic respiration, molecular oxygen (O2) serves as the terminal electron
acceptor at the end of the electron transport chain. This reduction results in the formation
of water as a byproduct. Anaerobic respiration would utilize different inorganic molecules
like nitrate or sulfate as acceptors.
4. Which phase of the bacterial growth curve is characterized by a period of little to no cell
division as the population adapts to a new environment?
A. Log phase
B. Stationary phase
C. Lag phase
D. Death phase
Correct Answer: C
Explanation: The lag phase represents the initial period where cells are metabolically
active but not yet dividing. During this time, bacteria are synthesizing necessary enzymes
and proteins to utilize the available nutrients in the medium. The duration of this phase
varies depending on the species and the shift in environmental conditions.
5. In DNA replication, which enzyme is responsible for unwinding the double helix at the
replication fork?
A. DNA Polymerase III
B. Ligase
C. Primase
D. Helicase
Correct Answer: D
Explanation: Helicase is the enzyme that breaks the hydrogen bonds between the
nitrogenous bases to separate the two DNA strands. This creates the replication fork where
other enzymes like DNA polymerase can begin synthesis. Single-strand binding proteins
then stabilize the unwound DNA to prevent it from re-annealing.
6. Which of the following are products of the Krebs cycle (Citric Acid Cycle) per one turn?
(Select all that apply)
A. 2 molecules of CO2
B. 3 molecules of NADH
, C. 1 molecule of FADH2
D. 1 molecule of ATP (or GTP)
E. 2 molecules of Pyruvate
Correct Answer: A,B,C,D
Explanation: The Krebs cycle processes one Acetyl-CoA per turn, releasing two CO2
molecules as waste. It also generates high-energy electron carriers in the form of three
NADH and one FADH2. A single molecule of ATP or GTP is produced through substrate-
level phosphorylation during the cycle.
7. A mutation that results in the insertion of a single nucleotide into a DNA sequence is most
likely to cause what type of effect?
A. Frameshift mutation
B. Missense mutation
C. Silent mutation
D. Nonsense mutation
Correct Answer: A
Explanation: An insertion or deletion of nucleotides not in multiples of three shifts the
reading frame of the mRNA codons. This frameshift usually leads to a completely different
amino acid sequence downstream and often creates a premature stop codon. Such
mutations are typically deleterious to the function of the resulting protein.
8. Which process involves the transfer of DNA from a donor to a recipient cell via a
bacteriophage?
A. Transformation
B. Conjugation
C. Translation
D. Transduction
Correct Answer: D
Explanation: Transduction is a mechanism of horizontal gene transfer where bacterial
DNA is packaged into a viral capsid by mistake during phage assembly. When this phage
infects a new host, it injects the bacterial DNA instead of viral DNA. This process allows for
genetic recombination between different bacterial cells.
9. What is the net gain of ATP molecules produced during glycolysis from a single molecule of
glucose?
A. 36 ATP
