BIOD 171 | BIOD 171 Microbiology Module 2 Exam
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which of the following terms describes a spherical-shaped bacterial cell?
A. Bacillus
B. Vibrio
C. Spirillum
D. Coccus
Correct Answer: D
Expert Explanation: Bacterial morphology is one of the most basic ways to classify
microorganisms. A coccus is defined as a bacterium that has a spherical or ovoid
shape. In contrast, a bacillus is rod-shaped, and a spirillum is spiral-shaped.
Identification of these shapes is the first step in the laboratory diagnosis of bacterial
infections. Proper classification allows clinicians to predict the behavior and
potential pathogenicity of the organism.
2. Which component is the primary structural molecule found in the bacterial cell
wall?
A. Peptidoglycan
B. Cellulose
,C. Chitin
D. Glycogen
Correct Answer: A
Expert Explanation: Peptidoglycan is a complex polymer consisting of sugars and
amino acids that forms a mesh-like layer outside the plasma membrane. It provides
structural strength and protects the cell from osmotic pressure changes. While
plants use cellulose and fungi use chitin, bacteria uniquely utilize peptidoglycan for
their cell walls. This molecule is a major target for many antibiotic classes, such as
penicillins. Without a functional cell wall, the bacterial cell would likely undergo
lysis and die.
3. Gram-positive bacteria are characterized by which of the following structural
features?
A. A thin layer of peptidoglycan and an outer membrane
B. An outer membrane containing porins
C. The presence of lipopolysaccharides (LPS)
D. A thick layer of peptidoglycan and no outer membrane
Correct Answer: D
,Expert Explanation: Gram-positive bacteria possess a cell wall that is
predominantly composed of a thick peptidoglycan layer. Unlike Gram-negative
bacteria, they lack an outer lipid membrane and the associated lipopolysaccharides.
This thick layer effectively traps the crystal violet dye during the Gram staining
procedure. Consequently, these bacteria appear purple or blue under a light
microscope. Understanding this structural difference is crucial for selecting effective
antimicrobial therapies.
4. What is the function of the bacterial capsule?
A. Assisting in DNA replication
B. Providing a site for protein synthesis
C. Regulating the transport of ions
D. Protecting the cell from phagocytosis
Correct Answer: D
Expert Explanation: The capsule is an organized layer of glycocalyx that sits
outside the bacterial cell wall. Its primary role is to protect the bacterium from the
host’s immune system, specifically phagocytic white blood cells. By masking the
surface antigens, the capsule increases the virulence of the pathogen. It also helps
the bacteria adhere to surfaces and prevents dehydration in harsh environments.
, Laboratory identification often uses specific stains to visualize this protective outer
layer.
5. Which bacterial structure is used primarily for motility?
A. Flagella
B. Pili
C. Fimbriae
D. Ribosomes
Correct Answer: A
Expert Explanation: Flagella are long, whip-like appendages that rotate to propel
the bacterial cell through liquid environments. They allow the organism to move
toward nutrients or away from toxic substances via chemotaxis. While fimbriae and
pili are also surface appendages, they are used for attachment and genetic exchange
rather than movement. The arrangement and number of flagella can vary
significantly between different bacterial species. Motility is a key characteristic used
in the phenotypic classification of bacteria.
6. What is the primary function of fimbriae in bacteria?
A. Bacterial reproduction
B. Movement through liquid
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which of the following terms describes a spherical-shaped bacterial cell?
A. Bacillus
B. Vibrio
C. Spirillum
D. Coccus
Correct Answer: D
Expert Explanation: Bacterial morphology is one of the most basic ways to classify
microorganisms. A coccus is defined as a bacterium that has a spherical or ovoid
shape. In contrast, a bacillus is rod-shaped, and a spirillum is spiral-shaped.
Identification of these shapes is the first step in the laboratory diagnosis of bacterial
infections. Proper classification allows clinicians to predict the behavior and
potential pathogenicity of the organism.
2. Which component is the primary structural molecule found in the bacterial cell
wall?
A. Peptidoglycan
B. Cellulose
,C. Chitin
D. Glycogen
Correct Answer: A
Expert Explanation: Peptidoglycan is a complex polymer consisting of sugars and
amino acids that forms a mesh-like layer outside the plasma membrane. It provides
structural strength and protects the cell from osmotic pressure changes. While
plants use cellulose and fungi use chitin, bacteria uniquely utilize peptidoglycan for
their cell walls. This molecule is a major target for many antibiotic classes, such as
penicillins. Without a functional cell wall, the bacterial cell would likely undergo
lysis and die.
3. Gram-positive bacteria are characterized by which of the following structural
features?
A. A thin layer of peptidoglycan and an outer membrane
B. An outer membrane containing porins
C. The presence of lipopolysaccharides (LPS)
D. A thick layer of peptidoglycan and no outer membrane
Correct Answer: D
,Expert Explanation: Gram-positive bacteria possess a cell wall that is
predominantly composed of a thick peptidoglycan layer. Unlike Gram-negative
bacteria, they lack an outer lipid membrane and the associated lipopolysaccharides.
This thick layer effectively traps the crystal violet dye during the Gram staining
procedure. Consequently, these bacteria appear purple or blue under a light
microscope. Understanding this structural difference is crucial for selecting effective
antimicrobial therapies.
4. What is the function of the bacterial capsule?
A. Assisting in DNA replication
B. Providing a site for protein synthesis
C. Regulating the transport of ions
D. Protecting the cell from phagocytosis
Correct Answer: D
Expert Explanation: The capsule is an organized layer of glycocalyx that sits
outside the bacterial cell wall. Its primary role is to protect the bacterium from the
host’s immune system, specifically phagocytic white blood cells. By masking the
surface antigens, the capsule increases the virulence of the pathogen. It also helps
the bacteria adhere to surfaces and prevents dehydration in harsh environments.
, Laboratory identification often uses specific stains to visualize this protective outer
layer.
5. Which bacterial structure is used primarily for motility?
A. Flagella
B. Pili
C. Fimbriae
D. Ribosomes
Correct Answer: A
Expert Explanation: Flagella are long, whip-like appendages that rotate to propel
the bacterial cell through liquid environments. They allow the organism to move
toward nutrients or away from toxic substances via chemotaxis. While fimbriae and
pili are also surface appendages, they are used for attachment and genetic exchange
rather than movement. The arrangement and number of flagella can vary
significantly between different bacterial species. Motility is a key characteristic used
in the phenotypic classification of bacteria.
6. What is the primary function of fimbriae in bacteria?
A. Bacterial reproduction
B. Movement through liquid
