BIOL 3200 Exam 1 Actual Exam V1 | BIOL 3200 General Microbiology
(BIOL 3200 Exam 1) | Auburn University
1. Who was the first person to provide a detailed description of bacteria, calling them ‘wee
animalcules’?
A. Robert Hooke
B. Antonie van Leeuwenhoek
C. Louis Pasteur
D. Robert Koch
Answer: B
Rationale: Antonie van Leeuwenhoek is credited as the first person to visualize bacteria
using high-quality simple microscopes he designed. Robert Hooke preceded him but only
observed larger molds and cells in cork. This discovery laid the foundation for the field of
microbiology by proving a microscopic world existed.
2. Which scientist definitively disproved the theory of spontaneous generation using a swan-
necked flask?
A. Ferdinand Cohn
B. Louis Pasteur
C. Robert Koch
D. Lazzaro Spallanzani
Answer: B
Rationale: Louis Pasteur’s experiment demonstrated that microorganisms in the air were
responsible for contaminating infusions rather than appearing spontaneously. The swan-
necked flask allowed air to enter but trapped dust and microbes in the neck, keeping the
broth sterile. This work was pivotal in establishing the germ theory of disease and modern
sterilization techniques.
3. The three-domain system of classification (Bacteria, Archaea, and Eukarya) is based
primarily on the sequence analysis of which molecule?
A. Transfer RNA (tRNA)
B. Adenosine triphosphate (ATP)
C. Ribosomal RNA (16S/18S rRNA)
D. Messenger RNA (mRNA)
,E. Peptidoglycan
Answer: C
Rationale: Carl Woese pioneered the use of 16S ribosomal RNA as a molecular
chronometer to determine evolutionary relationships. Ribosomal RNA is ideal because it is
universally distributed, functionally constant, and highly conserved. This approach
revealed that Archaea are a distinct domain of life, separate from both Bacteria and
Eukarya.
4. Which of Koch’s postulates requires the pathogen to be isolated from a diseased host and
grown in a pure culture?
A. Postulate 2
B. Postulate 1
C. Postulate 3
D. Postulate 4
Answer: A
Rationale: Koch’s second postulate states that the suspected pathogen must be isolated
and grown in a pure culture outside the host. This step is critical because it allows
researchers to characterize the specific microbe without interference from others. Without
a pure culture, one cannot definitively link a specific organism to a specific disease
symptoms.
5. What is the resolution limit of a standard light microscope?
A. Both A and D are correct
B. 2.0 micrometers
C. 0.02 micrometers
D. 200 nanometers
E. 0.2 micrometers
Answer: A
Rationale: The resolution limit of a light microscope is determined by the wavelength of
light and the numerical aperture of the lens. For standard visible light, this limit is
approximately 0.2 micrometers, which is equivalent to 200 nanometers. Beyond this limit,
two distinct points will appear as one, necessitating the use of electron microscopy for
smaller structures.
6. In the Gram stain procedure, what is the role of iodine?
A. Primary stain
B. Counterstain
, C. Mordant
D. Decolorizer
Answer: C
Rationale: Iodine acts as a mordant that reacts with crystal violet to form a large, insoluble
CV-I complex. In Gram-positive cells, this complex is trapped within the thick peptidoglycan
layer during decolorization. In Gram-negative cells, the thin peptidoglycan layer and thin
outer membrane cannot retain the complex after alcohol treatment.
7. Which bacterial structure is specifically designed for survival under extreme environmental
conditions like heat and radiation?
A. Flagella
B. Gas vesicle
C. Capsule
D. Endospore
Answer: D
Rationale: Endospores are highly differentiated cells that are extremely resistant to heat,
harsh chemicals, and radiation. They are produced by certain Gram-positive bacteria, such
as members of the genera Bacillus and Clostridium. The spore contains dipicolinic acid and
calcium, which help stabilize the DNA and provide dehydration for heat resistance.
8. What is the primary chemical component of the bacterial cell wall?
A. Cellulose
B. Chitin
C. Pseudomurein
D. Peptidoglycan
Answer: D
Rationale: Peptidoglycan, also known as murein, is a unique polysaccharide composed of
alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues. These
chains are cross-linked by short peptides to provide structural strength and prevent
osmotic lysis. This molecule is found only in Bacteria and serves as a major target for
antibiotics like penicillin.
9. Which of the following describes the arrangement of flagella distributed over the entire
surface of a bacterial cell?
A. Monotrichous
B. Lophotrichous
(BIOL 3200 Exam 1) | Auburn University
1. Who was the first person to provide a detailed description of bacteria, calling them ‘wee
animalcules’?
A. Robert Hooke
B. Antonie van Leeuwenhoek
C. Louis Pasteur
D. Robert Koch
Answer: B
Rationale: Antonie van Leeuwenhoek is credited as the first person to visualize bacteria
using high-quality simple microscopes he designed. Robert Hooke preceded him but only
observed larger molds and cells in cork. This discovery laid the foundation for the field of
microbiology by proving a microscopic world existed.
2. Which scientist definitively disproved the theory of spontaneous generation using a swan-
necked flask?
A. Ferdinand Cohn
B. Louis Pasteur
C. Robert Koch
D. Lazzaro Spallanzani
Answer: B
Rationale: Louis Pasteur’s experiment demonstrated that microorganisms in the air were
responsible for contaminating infusions rather than appearing spontaneously. The swan-
necked flask allowed air to enter but trapped dust and microbes in the neck, keeping the
broth sterile. This work was pivotal in establishing the germ theory of disease and modern
sterilization techniques.
3. The three-domain system of classification (Bacteria, Archaea, and Eukarya) is based
primarily on the sequence analysis of which molecule?
A. Transfer RNA (tRNA)
B. Adenosine triphosphate (ATP)
C. Ribosomal RNA (16S/18S rRNA)
D. Messenger RNA (mRNA)
,E. Peptidoglycan
Answer: C
Rationale: Carl Woese pioneered the use of 16S ribosomal RNA as a molecular
chronometer to determine evolutionary relationships. Ribosomal RNA is ideal because it is
universally distributed, functionally constant, and highly conserved. This approach
revealed that Archaea are a distinct domain of life, separate from both Bacteria and
Eukarya.
4. Which of Koch’s postulates requires the pathogen to be isolated from a diseased host and
grown in a pure culture?
A. Postulate 2
B. Postulate 1
C. Postulate 3
D. Postulate 4
Answer: A
Rationale: Koch’s second postulate states that the suspected pathogen must be isolated
and grown in a pure culture outside the host. This step is critical because it allows
researchers to characterize the specific microbe without interference from others. Without
a pure culture, one cannot definitively link a specific organism to a specific disease
symptoms.
5. What is the resolution limit of a standard light microscope?
A. Both A and D are correct
B. 2.0 micrometers
C. 0.02 micrometers
D. 200 nanometers
E. 0.2 micrometers
Answer: A
Rationale: The resolution limit of a light microscope is determined by the wavelength of
light and the numerical aperture of the lens. For standard visible light, this limit is
approximately 0.2 micrometers, which is equivalent to 200 nanometers. Beyond this limit,
two distinct points will appear as one, necessitating the use of electron microscopy for
smaller structures.
6. In the Gram stain procedure, what is the role of iodine?
A. Primary stain
B. Counterstain
, C. Mordant
D. Decolorizer
Answer: C
Rationale: Iodine acts as a mordant that reacts with crystal violet to form a large, insoluble
CV-I complex. In Gram-positive cells, this complex is trapped within the thick peptidoglycan
layer during decolorization. In Gram-negative cells, the thin peptidoglycan layer and thin
outer membrane cannot retain the complex after alcohol treatment.
7. Which bacterial structure is specifically designed for survival under extreme environmental
conditions like heat and radiation?
A. Flagella
B. Gas vesicle
C. Capsule
D. Endospore
Answer: D
Rationale: Endospores are highly differentiated cells that are extremely resistant to heat,
harsh chemicals, and radiation. They are produced by certain Gram-positive bacteria, such
as members of the genera Bacillus and Clostridium. The spore contains dipicolinic acid and
calcium, which help stabilize the DNA and provide dehydration for heat resistance.
8. What is the primary chemical component of the bacterial cell wall?
A. Cellulose
B. Chitin
C. Pseudomurein
D. Peptidoglycan
Answer: D
Rationale: Peptidoglycan, also known as murein, is a unique polysaccharide composed of
alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) residues. These
chains are cross-linked by short peptides to provide structural strength and prevent
osmotic lysis. This molecule is found only in Bacteria and serves as a major target for
antibiotics like penicillin.
9. Which of the following describes the arrangement of flagella distributed over the entire
surface of a bacterial cell?
A. Monotrichous
B. Lophotrichous
