BIOL 3200 Exam 1 Actual Exam V2 | BIOL 3200 General Microbiology
(BIOL 3200 Exam 1) | Auburn University
1. Which scientist is credited with definitively disproving the theory of spontaneous
generation using a swan-necked flask?
A. Robert Koch
B. Ignaz Semmelweis
C. Antonie van Leeuwenhoek
D. Louis Pasteur
Answer: D
Rationale: Louis Pasteur used swan-necked flasks to show that microbes in the air were
responsible for contamination. His experiments demonstrated that life does not arise from
non-living matter, effectively ending the debate on spontaneous generation. This work
paved the way for the germ theory of disease and modern sterilization practices.
2. In microscopy, what is the primary purpose of using immersion oil with the 100x objective
lens?
A. To increase the numerical aperture and resolution
B. To increase the magnification of the image
C. To decrease the refractive index of the medium
D. To lubricate the lens surface
Answer: A
Rationale: Immersion oil has the same refractive index as glass, which prevents the
bending of light as it passes from the slide to the lens. By capturing more light rays, the oil
increases the numerical aperture of the system. This directly improves the resolution,
allowing for a clearer image of fine details in bacterial cells.
3. Which of the following components is unique to the cell walls of Gram-positive bacteria?
A. Lipopolysaccharides
B. Outer membrane
C. Periplasmic space
D. Teichoic acids
Answer: D
,Rationale: Teichoic acids are acidic polysaccharides covalently linked to the thick
peptidoglycan layer in Gram-positive bacteria. They play essential roles in cell wall
maintenance, ion regulation, and cell division processes. In contrast, Gram-negative
bacteria lack these molecules but possess an outer membrane and lipopolysaccharides.
4. What is the primary energy source that drives the rotation of the bacterial flagellum?
A. ATP hydrolysis
B. GTP hydrolysis
C. Proton motive force
D. Phosphoenolpyruvate
Answer: C
Rationale: The bacterial flagellum functions like a tiny electric motor powered by the flow
of protons across the cytoplasmic membrane. This proton motive force (PMF) provides the
electrochemical energy necessary for the basal body to rotate. Unlike eukaryotic flagella
which use ATP, the prokaryotic flagellar motor is highly efficient and dependent on ion
gradients.
5. A bacterium that grows optimally at a temperature of 15°C and cannot grow above 20°C is
classified as a:
A. Mesophile
B. Psychrotolerant
C. Thermophile
D. Psychrophile
Answer: D
Rationale: Psychrophiles are extremophilic organisms that thrive in cold environments
like the Arctic or deep ocean. They possess specialized enzymes and membranes rich in
unsaturated fatty acids to remain functional at low temperatures. If exposed to
temperatures above 20°C, their proteins typically denature and their membranes lose
integrity.
6. Which phase of the microbial growth curve is characterized by a constant, maximal rate of
cell division?
A. Lag phase
B. Stationary phase
C. Log (Exponential) phase
D. Death phase
, Answer: C
Rationale: During the log phase, bacteria adjust to their environment and begin dividing at
their shortest possible generation time. The population increases exponentially, making
this the ideal stage for biochemical and physiological studies. The growth rate is limited
only by the genetics of the organism and the availability of nutrients.
7. Which component of the Lipopolysaccharide (LPS) is responsible for the toxic effects
associated with Gram-negative infections?
A. O-specific polysaccharide
B. Core polysaccharide
C. Porins
D. Lipid A
Answer: D
Rationale: Lipid A is the innermost portion of the LPS and acts as a potent endotoxin when
released into the host bloodstream. It triggers a massive immune response that can lead to
fever, inflammation, and septic shock. While the O-antigen is used for serotyping, Lipid A is
the primary factor driving the pathogenesis of Gram-negative sepsis.
8. The bacterial cell wall is composed of a repeating lattice of two amino sugars. What are
they?
A. Glucose and Fructose
B. Peptide and Glycan
C. N-acetylglucosamine and N-acetylmuramic acid
D. Ribose and Deoxyribose
Answer: C
Rationale: Peptidoglycan consists of alternating units of N-acetylglucosamine (NAG) and
N-acetylmuramic acid (NAM) linked by beta-1,4-glycosidic bonds. These glycan chains are
cross-linked by short peptides to provide structural rigidity and protect the cell from
osmotic lysis. This unique structure is the target of many antibiotics, such as penicillin.
9. Which of the following microscopy techniques is best suited for viewing the internal
structures of a virus?
A. Bright-field microscopy
B. Scanning electron microscopy (SEM)
C. Phase-contrast microscopy
D. Transmission electron microscopy (TEM)
(BIOL 3200 Exam 1) | Auburn University
1. Which scientist is credited with definitively disproving the theory of spontaneous
generation using a swan-necked flask?
A. Robert Koch
B. Ignaz Semmelweis
C. Antonie van Leeuwenhoek
D. Louis Pasteur
Answer: D
Rationale: Louis Pasteur used swan-necked flasks to show that microbes in the air were
responsible for contamination. His experiments demonstrated that life does not arise from
non-living matter, effectively ending the debate on spontaneous generation. This work
paved the way for the germ theory of disease and modern sterilization practices.
2. In microscopy, what is the primary purpose of using immersion oil with the 100x objective
lens?
A. To increase the numerical aperture and resolution
B. To increase the magnification of the image
C. To decrease the refractive index of the medium
D. To lubricate the lens surface
Answer: A
Rationale: Immersion oil has the same refractive index as glass, which prevents the
bending of light as it passes from the slide to the lens. By capturing more light rays, the oil
increases the numerical aperture of the system. This directly improves the resolution,
allowing for a clearer image of fine details in bacterial cells.
3. Which of the following components is unique to the cell walls of Gram-positive bacteria?
A. Lipopolysaccharides
B. Outer membrane
C. Periplasmic space
D. Teichoic acids
Answer: D
,Rationale: Teichoic acids are acidic polysaccharides covalently linked to the thick
peptidoglycan layer in Gram-positive bacteria. They play essential roles in cell wall
maintenance, ion regulation, and cell division processes. In contrast, Gram-negative
bacteria lack these molecules but possess an outer membrane and lipopolysaccharides.
4. What is the primary energy source that drives the rotation of the bacterial flagellum?
A. ATP hydrolysis
B. GTP hydrolysis
C. Proton motive force
D. Phosphoenolpyruvate
Answer: C
Rationale: The bacterial flagellum functions like a tiny electric motor powered by the flow
of protons across the cytoplasmic membrane. This proton motive force (PMF) provides the
electrochemical energy necessary for the basal body to rotate. Unlike eukaryotic flagella
which use ATP, the prokaryotic flagellar motor is highly efficient and dependent on ion
gradients.
5. A bacterium that grows optimally at a temperature of 15°C and cannot grow above 20°C is
classified as a:
A. Mesophile
B. Psychrotolerant
C. Thermophile
D. Psychrophile
Answer: D
Rationale: Psychrophiles are extremophilic organisms that thrive in cold environments
like the Arctic or deep ocean. They possess specialized enzymes and membranes rich in
unsaturated fatty acids to remain functional at low temperatures. If exposed to
temperatures above 20°C, their proteins typically denature and their membranes lose
integrity.
6. Which phase of the microbial growth curve is characterized by a constant, maximal rate of
cell division?
A. Lag phase
B. Stationary phase
C. Log (Exponential) phase
D. Death phase
, Answer: C
Rationale: During the log phase, bacteria adjust to their environment and begin dividing at
their shortest possible generation time. The population increases exponentially, making
this the ideal stage for biochemical and physiological studies. The growth rate is limited
only by the genetics of the organism and the availability of nutrients.
7. Which component of the Lipopolysaccharide (LPS) is responsible for the toxic effects
associated with Gram-negative infections?
A. O-specific polysaccharide
B. Core polysaccharide
C. Porins
D. Lipid A
Answer: D
Rationale: Lipid A is the innermost portion of the LPS and acts as a potent endotoxin when
released into the host bloodstream. It triggers a massive immune response that can lead to
fever, inflammation, and septic shock. While the O-antigen is used for serotyping, Lipid A is
the primary factor driving the pathogenesis of Gram-negative sepsis.
8. The bacterial cell wall is composed of a repeating lattice of two amino sugars. What are
they?
A. Glucose and Fructose
B. Peptide and Glycan
C. N-acetylglucosamine and N-acetylmuramic acid
D. Ribose and Deoxyribose
Answer: C
Rationale: Peptidoglycan consists of alternating units of N-acetylglucosamine (NAG) and
N-acetylmuramic acid (NAM) linked by beta-1,4-glycosidic bonds. These glycan chains are
cross-linked by short peptides to provide structural rigidity and protect the cell from
osmotic lysis. This unique structure is the target of many antibiotics, such as penicillin.
9. Which of the following microscopy techniques is best suited for viewing the internal
structures of a virus?
A. Bright-field microscopy
B. Scanning electron microscopy (SEM)
C. Phase-contrast microscopy
D. Transmission electron microscopy (TEM)
