BIOL 271 | BIOL271 Module 2: Microbiology
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. Which term describes the sum of all chemical reactions within a living organism?
A. Metabolism
B. Catabolism
C. Anabolism
D. Photosynthesis
Correct Answer: A
Explanation: Metabolism encompasses every biochemical reaction that occurs within a
cell to maintain life. It is traditionally divided into two main parts known as catabolism and
anabolism. Catabolic pathways break down complex molecules into simpler ones to release
energy. Anabolic pathways use that energy to build complex cellular components from
simpler precursors. Together, these processes manage the energy and material resources
of the microbial cell.
2. In the microbial growth curve, which phase is characterized by a rapid increase in cell
number?
A. Lag phase
B. Stationary phase
C. Log phase
D. Death phase
Correct Answer: C
Explanation: The log phase is also referred to as the exponential growth phase where cells
divide at a constant rate. During this time, the generation time reaches its minimum and
remains constant for the population. Microbial metabolism is most efficient during this
phase because nutrients are abundant and waste products are low. This phase is the ideal
time to perform gram stains or test antibiotic susceptibility. The growth follows a
geometric progression as cells double during each generation cycle.
3. What is the net gain of ATP molecules produced during the process of glycolysis for one
molecule of glucose?
A. 36 ATP
B. 4 ATP
C. 2 ATP
,D. 38 ATP
Correct Answer: C
Explanation: Glycolysis begins by utilizing two ATP molecules to phosphorylate glucose
during the energy investment stage. As the pathway progresses, four ATP molecules are
eventually synthesized through substrate-level phosphorylation. Subtracting the initial
investment from the total production results in a net gain of two ATP. This process also
generates two molecules of NADH which carry electrons to the electron transport chain.
Glycolysis is a universal pathway used by both aerobic and anaerobic microorganisms to
extract energy.
4. Which group of microorganisms thrives in environments with temperatures ranging from
45°C to 80°C?
A. Thermophiles
B. Mesophiles
C. Psychrophiles
D. Hyperthermophiles
Correct Answer: A
Explanation: Thermophiles are heat-loving organisms that have adapted to high-
temperature environments such as hot springs. Their enzymes and proteins are specifically
structured to remain stable and functional at these elevated temperatures. Unlike
mesophiles, which prefer body temperature, thermophiles would grow very slowly or not
at all at 37 degrees Celsius. These organisms are often found in compost piles and hot
water heaters. Their membranes contain saturated fatty acids to prevent them from
becoming too fluid in the heat.
5. What is the primary role of an enzyme in a metabolic reaction?
A. To decrease the activation energy
B. To increase the activation energy
C. To provide energy for the reaction
D. To change the equilibrium of the reaction
Correct Answer: A
Explanation: Enzymes act as biological catalysts that speed up chemical reactions without
being consumed in the process. They achieve this by lowering the activation energy barrier
required for a reaction to proceed. This allows metabolic processes to occur rapidly at
temperatures compatible with life. Enzymes are highly specific to their substrates due to
the unique shape of their active sites. Without enzymes, most cellular reactions would
occur too slowly to sustain the organism.
, 6. Microbes that require high salt concentrations for growth are known as:
A. Capnophiles
B. Acidophiles
C. Barophiles
D. Halophiles
Correct Answer: D
Explanation: Halophiles are organisms that are adapted to live in environments with high
osmotic pressure. Obligate halophiles actually require high concentrations of sodium
chloride to maintain the integrity of their cell walls. These organisms are commonly found
in locations like the Great Salt Lake or the Dead Sea. Most bacteria would undergo
plasmolysis in such high salt environments because water would leave the cell. Halophiles
accumulate internal solutes to balance the external osmotic pressure and prevent
dehydration.
7. Which phase of the bacterial growth curve occurs when the rate of cell division equals the
rate of cell death?
A. Lag phase
B. Log phase
C. Stationary phase
D. Decline phase
Correct Answer: C
Explanation: During the stationary phase, the population size stabilizes as the number of
new cells being created matches the number dying. This plateau is caused by the depletion
of essential nutrients and the accumulation of toxic waste products. Changes in pH and
limited oxygen availability also contribute to the cessation of exponential growth. Cells in
this phase often undergo metabolic changes to survive stressful conditions. Some species
may begin to form endospores or produce secondary metabolites like antibiotics during
this time.
8. An organism that uses light as an energy source and carbon dioxide as a carbon source is a:
A. Chemoautotroph
B. Chemoheterotroph
C. Photoheterotroph
D. Photoautotroph
Correct Answer: D
Updated and Latest Questions and Correct
Answers with Rationale - Portage Learning
1. Which term describes the sum of all chemical reactions within a living organism?
A. Metabolism
B. Catabolism
C. Anabolism
D. Photosynthesis
Correct Answer: A
Explanation: Metabolism encompasses every biochemical reaction that occurs within a
cell to maintain life. It is traditionally divided into two main parts known as catabolism and
anabolism. Catabolic pathways break down complex molecules into simpler ones to release
energy. Anabolic pathways use that energy to build complex cellular components from
simpler precursors. Together, these processes manage the energy and material resources
of the microbial cell.
2. In the microbial growth curve, which phase is characterized by a rapid increase in cell
number?
A. Lag phase
B. Stationary phase
C. Log phase
D. Death phase
Correct Answer: C
Explanation: The log phase is also referred to as the exponential growth phase where cells
divide at a constant rate. During this time, the generation time reaches its minimum and
remains constant for the population. Microbial metabolism is most efficient during this
phase because nutrients are abundant and waste products are low. This phase is the ideal
time to perform gram stains or test antibiotic susceptibility. The growth follows a
geometric progression as cells double during each generation cycle.
3. What is the net gain of ATP molecules produced during the process of glycolysis for one
molecule of glucose?
A. 36 ATP
B. 4 ATP
C. 2 ATP
,D. 38 ATP
Correct Answer: C
Explanation: Glycolysis begins by utilizing two ATP molecules to phosphorylate glucose
during the energy investment stage. As the pathway progresses, four ATP molecules are
eventually synthesized through substrate-level phosphorylation. Subtracting the initial
investment from the total production results in a net gain of two ATP. This process also
generates two molecules of NADH which carry electrons to the electron transport chain.
Glycolysis is a universal pathway used by both aerobic and anaerobic microorganisms to
extract energy.
4. Which group of microorganisms thrives in environments with temperatures ranging from
45°C to 80°C?
A. Thermophiles
B. Mesophiles
C. Psychrophiles
D. Hyperthermophiles
Correct Answer: A
Explanation: Thermophiles are heat-loving organisms that have adapted to high-
temperature environments such as hot springs. Their enzymes and proteins are specifically
structured to remain stable and functional at these elevated temperatures. Unlike
mesophiles, which prefer body temperature, thermophiles would grow very slowly or not
at all at 37 degrees Celsius. These organisms are often found in compost piles and hot
water heaters. Their membranes contain saturated fatty acids to prevent them from
becoming too fluid in the heat.
5. What is the primary role of an enzyme in a metabolic reaction?
A. To decrease the activation energy
B. To increase the activation energy
C. To provide energy for the reaction
D. To change the equilibrium of the reaction
Correct Answer: A
Explanation: Enzymes act as biological catalysts that speed up chemical reactions without
being consumed in the process. They achieve this by lowering the activation energy barrier
required for a reaction to proceed. This allows metabolic processes to occur rapidly at
temperatures compatible with life. Enzymes are highly specific to their substrates due to
the unique shape of their active sites. Without enzymes, most cellular reactions would
occur too slowly to sustain the organism.
, 6. Microbes that require high salt concentrations for growth are known as:
A. Capnophiles
B. Acidophiles
C. Barophiles
D. Halophiles
Correct Answer: D
Explanation: Halophiles are organisms that are adapted to live in environments with high
osmotic pressure. Obligate halophiles actually require high concentrations of sodium
chloride to maintain the integrity of their cell walls. These organisms are commonly found
in locations like the Great Salt Lake or the Dead Sea. Most bacteria would undergo
plasmolysis in such high salt environments because water would leave the cell. Halophiles
accumulate internal solutes to balance the external osmotic pressure and prevent
dehydration.
7. Which phase of the bacterial growth curve occurs when the rate of cell division equals the
rate of cell death?
A. Lag phase
B. Log phase
C. Stationary phase
D. Decline phase
Correct Answer: C
Explanation: During the stationary phase, the population size stabilizes as the number of
new cells being created matches the number dying. This plateau is caused by the depletion
of essential nutrients and the accumulation of toxic waste products. Changes in pH and
limited oxygen availability also contribute to the cessation of exponential growth. Cells in
this phase often undergo metabolic changes to survive stressful conditions. Some species
may begin to form endospores or produce secondary metabolites like antibiotics during
this time.
8. An organism that uses light as an energy source and carbon dioxide as a carbon source is a:
A. Chemoautotroph
B. Chemoheterotroph
C. Photoheterotroph
D. Photoautotroph
Correct Answer: D
