BIOL 3200 Exam 1 Actual Exam V3 | BIOL 3200 General Microbiology
(BIOL 3200 Exam 1) | Auburn University
1. Which of the following describes the ability of a microscope to distinguish two adjacent
points as separate entities?
A. Magnification
B. Contrast
C. Refractive Index
D. Resolution
Answer: D
Rationale: Resolution is the most important feature of a microscope for determining fine
detail. It is mathematically defined by the limit of resolution which depends on the
wavelength of light and the numerical aperture of the lens. Without sufficient resolution,
increasing magnification will only produce a larger, blurry image.
2. Carl Woese used which of the following molecules to establish the three-domain system of
classification?
A. Mitochondrial DNA
B. Peptidoglycan sequences
C. 16S ribosomal RNA
D. Phospholipid head groups
Answer: C
Rationale: The 16S rRNA molecule is highly conserved across all prokaryotes and provides
a molecular clock for evolutionary timing. By comparing these sequences, Woese
discovered that Archaea were distinct from both Bacteria and Eukarya. This methodology
revolutionized taxonomy by moving away from morphological traits toward genetic
phylogeny.
3. In a Gram-stain procedure, what is the specific role of iodine?
A. Primary stain
B. Counterstain
C. Decolorizer
D. Mordant
Answer: D
,Rationale: Iodine acts as a mordant by forming a large complex with the crystal violet
primary stain inside the cell. This CV-I complex is too large to easily wash out of the thick
peptidoglycan layer of Gram-positive cells. If this step is skipped, the primary stain will
wash away during the decolorization phase regardless of cell wall type.
4. A bacterium that grows optimally at 15 degrees Celsius and cannot grow above 20 degrees
Celsius is classified as a:
A. Psychrotroph
B. Mesophile
C. Psychrophile
D. Thermophile
Answer: C
Rationale: Psychrophiles are cold-loving organisms that thrive in environments like the
Arctic or deep ocean. They possess specialized enzymes and unsaturated fatty acids in their
membranes to maintain fluidity at low temperatures. Unlike psychrotrophs, they are
extremely sensitive to even moderate increases in heat.
5. Which component is unique to the cell walls of Acid-fast bacteria like Mycobacterium
tuberculosis?
A. Teichoic acids
B. Lipopolysaccharide
C. Mycolic acids
D. Periplasm
Answer: C
Rationale: Mycolic acids are waxy, long-chain fatty acids that provide a highly protective
barrier for certain bacteria. This waxy layer prevents the penetration of standard Gram
stain dyes, necessitating the use of heat or detergents in the Acid-fast stain. This structure
also contributes to the organism’s resistance to dehydration and many antibiotics.
6. During which phase of the bacterial growth curve is the population doubling at a constant,
maximum rate?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log (Exponential) phase
Answer: D
, Rationale: During the log phase, cells are in their most metabolically active state and are
dividing at their generation time. This phase is characterized by a straight line when the
cell numbers are plotted on a logarithmic scale. Most industrial and laboratory research
uses cells from this phase because they are physiologically uniform.
7. What is the primary function of bacterial endospores?
A. Reproduction
B. Survival in harsh conditions
C. Storage of nutrients
D. Increased motility
Answer: B
Rationale: Endospores are highly resistant, dormant structures produced by genera such
as Bacillus and Clostridium. They are not a reproductive strategy because one vegetative
cell produces only one spore. The spore contains dipicolinic acid and specialized proteins
that protect the DNA from UV, heat, and chemicals for decades.
8. An organism that uses light as an energy source and organic compounds as a carbon source
is a:
A. Photoautotroph
B. Chemoheterotroph
C. Chemolithotroph
D. Photoheterotroph
Answer: D
Rationale: Photoheterotrophs represent a unique metabolic group often found in aquatic
environments. While they capture light energy to generate ATP, they cannot fix CO2 and
must ingest organic molecules for their carbon skeleton. Examples include purple non-
sulfur bacteria.
9. Which structure facilitates the transfer of genetic material between two bacterial cells
during conjugation?
A. Fimbriae
B. Sex pilus
C. Flagella
D. Capsule
Answer: B
(BIOL 3200 Exam 1) | Auburn University
1. Which of the following describes the ability of a microscope to distinguish two adjacent
points as separate entities?
A. Magnification
B. Contrast
C. Refractive Index
D. Resolution
Answer: D
Rationale: Resolution is the most important feature of a microscope for determining fine
detail. It is mathematically defined by the limit of resolution which depends on the
wavelength of light and the numerical aperture of the lens. Without sufficient resolution,
increasing magnification will only produce a larger, blurry image.
2. Carl Woese used which of the following molecules to establish the three-domain system of
classification?
A. Mitochondrial DNA
B. Peptidoglycan sequences
C. 16S ribosomal RNA
D. Phospholipid head groups
Answer: C
Rationale: The 16S rRNA molecule is highly conserved across all prokaryotes and provides
a molecular clock for evolutionary timing. By comparing these sequences, Woese
discovered that Archaea were distinct from both Bacteria and Eukarya. This methodology
revolutionized taxonomy by moving away from morphological traits toward genetic
phylogeny.
3. In a Gram-stain procedure, what is the specific role of iodine?
A. Primary stain
B. Counterstain
C. Decolorizer
D. Mordant
Answer: D
,Rationale: Iodine acts as a mordant by forming a large complex with the crystal violet
primary stain inside the cell. This CV-I complex is too large to easily wash out of the thick
peptidoglycan layer of Gram-positive cells. If this step is skipped, the primary stain will
wash away during the decolorization phase regardless of cell wall type.
4. A bacterium that grows optimally at 15 degrees Celsius and cannot grow above 20 degrees
Celsius is classified as a:
A. Psychrotroph
B. Mesophile
C. Psychrophile
D. Thermophile
Answer: C
Rationale: Psychrophiles are cold-loving organisms that thrive in environments like the
Arctic or deep ocean. They possess specialized enzymes and unsaturated fatty acids in their
membranes to maintain fluidity at low temperatures. Unlike psychrotrophs, they are
extremely sensitive to even moderate increases in heat.
5. Which component is unique to the cell walls of Acid-fast bacteria like Mycobacterium
tuberculosis?
A. Teichoic acids
B. Lipopolysaccharide
C. Mycolic acids
D. Periplasm
Answer: C
Rationale: Mycolic acids are waxy, long-chain fatty acids that provide a highly protective
barrier for certain bacteria. This waxy layer prevents the penetration of standard Gram
stain dyes, necessitating the use of heat or detergents in the Acid-fast stain. This structure
also contributes to the organism’s resistance to dehydration and many antibiotics.
6. During which phase of the bacterial growth curve is the population doubling at a constant,
maximum rate?
A. Lag phase
B. Death phase
C. Stationary phase
D. Log (Exponential) phase
Answer: D
, Rationale: During the log phase, cells are in their most metabolically active state and are
dividing at their generation time. This phase is characterized by a straight line when the
cell numbers are plotted on a logarithmic scale. Most industrial and laboratory research
uses cells from this phase because they are physiologically uniform.
7. What is the primary function of bacterial endospores?
A. Reproduction
B. Survival in harsh conditions
C. Storage of nutrients
D. Increased motility
Answer: B
Rationale: Endospores are highly resistant, dormant structures produced by genera such
as Bacillus and Clostridium. They are not a reproductive strategy because one vegetative
cell produces only one spore. The spore contains dipicolinic acid and specialized proteins
that protect the DNA from UV, heat, and chemicals for decades.
8. An organism that uses light as an energy source and organic compounds as a carbon source
is a:
A. Photoautotroph
B. Chemoheterotroph
C. Chemolithotroph
D. Photoheterotroph
Answer: D
Rationale: Photoheterotrophs represent a unique metabolic group often found in aquatic
environments. While they capture light energy to generate ATP, they cannot fix CO2 and
must ingest organic molecules for their carbon skeleton. Examples include purple non-
sulfur bacteria.
9. Which structure facilitates the transfer of genetic material between two bacterial cells
during conjugation?
A. Fimbriae
B. Sex pilus
C. Flagella
D. Capsule
Answer: B
