BIOD 171 | BIOD 171 Microbiology Module 5 Exam
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which of the following best describes a virus in terms of its biological status?
A. Obligate intracellular parasite
B. Unicellular organism with a nucleus
C. Multicellular saprophytic organism
D. Free-living prokaryotic cell
Correct Answer: A
Expert Explanation: Viruses are categorized as obligate intracellular parasites
because they cannot replicate without a host cell. They lack the necessary metabolic
machinery to produce proteins or energy independently. Once they infect a host,
they hijack the cellular organelles to synthesize viral components. This unique
lifestyle distinguishes them from independent living organisms like bacteria or
fungi. This fundamental characteristic is central to understanding viral pathogenesis
and replication strategies.
2. What is the protein shell that surrounds and protects the viral genome called?
A. Plasmid
B. Envelope
,C. Spike
D. Capsid
Correct Answer: D
Expert Explanation: The protein shell known as a capsid serves as the primary
protective layer for a virus’s nucleic acid. It is composed of smaller protein subunits
called capsomeres that assemble into specific geometric shapes. The arrangement of
these subunits determines whether the virus is helical, icosahedral, or complex.
Beyond protection, the capsid plays a role in identifying and attaching to potential
host cells. It remains a defining structural feature used in the classification of
various viral families.
3. From where does an enveloped virus typically acquire its lipid membrane?
A. Synthesized de novo in the cytoplasm
B. Absorbed from the surrounding environment
C. Produced by the viral ribosomes
D. Taken from the host cell’s membrane
Correct Answer: D
Expert Explanation: The viral envelope is derived from the host cell’s own plasma
membrane or internal organelles during the budding process. As the virus exits the
,host cell, it wraps itself in a portion of the host lipid bilayer. This membrane often
contains host proteins alongside viral-specific glycoproteins or spikes. The presence
of an envelope can help the virus evade the host’s immune system by mimicking
host cell surfaces. However, it also makes the virus more susceptible to
environmental stressors like heat and detergents.
4. During the bacteriophage lytic cycle, what occurs immediately after the attachment
phase?
A. Assembly
B. Uncoating
C. Release
D. Entry (Penetration)
Correct Answer: D
Expert Explanation: After a bacteriophage successfully attaches to specific
receptors on the bacterial surface, it must inject its genetic material. This process is
known as entry or penetration, where the viral DNA or RNA crosses the cell wall.
Unlike animal viruses, many bacteriophages remain outside the cell while only the
genome enters. Once the genetic material is inside, the phage can begin the process
of hijacking host resources. This transition is a critical step in initiating a productive
infection cycle.
, 5. What is the defining characteristic of the lysogenic cycle in bacteriophages?
A. Immediate lysis of the host cell
B. Rapid production of thousands of virions
C. Integration of viral DNA into the host genome
D. The virus loses its capsid during replication
Correct Answer: C
Expert Explanation: In the lysogenic cycle, the viral DNA integrates into the host’s
bacterial chromosome rather than destroying it. Once integrated, the viral DNA is
referred to as a prophage and is replicated along with the bacterial genome. This
allow the virus to persist in a dormant state through many generations of bacterial
division. Certain environmental triggers can cause the prophage to excise and enter
the lytic cycle. This strategy enables the virus to survive even when host populations
are low or conditions are unfavorable.
6. Which enzyme is used by retroviruses like HIV to convert their RNA genome into
DNA?
A. Reverse transcriptase
B. DNA ligase
C. RNA polymerase
| Questions with Correct Answers and Expert
Explanation for Each Question | Portage Learning
1. Which of the following best describes a virus in terms of its biological status?
A. Obligate intracellular parasite
B. Unicellular organism with a nucleus
C. Multicellular saprophytic organism
D. Free-living prokaryotic cell
Correct Answer: A
Expert Explanation: Viruses are categorized as obligate intracellular parasites
because they cannot replicate without a host cell. They lack the necessary metabolic
machinery to produce proteins or energy independently. Once they infect a host,
they hijack the cellular organelles to synthesize viral components. This unique
lifestyle distinguishes them from independent living organisms like bacteria or
fungi. This fundamental characteristic is central to understanding viral pathogenesis
and replication strategies.
2. What is the protein shell that surrounds and protects the viral genome called?
A. Plasmid
B. Envelope
,C. Spike
D. Capsid
Correct Answer: D
Expert Explanation: The protein shell known as a capsid serves as the primary
protective layer for a virus’s nucleic acid. It is composed of smaller protein subunits
called capsomeres that assemble into specific geometric shapes. The arrangement of
these subunits determines whether the virus is helical, icosahedral, or complex.
Beyond protection, the capsid plays a role in identifying and attaching to potential
host cells. It remains a defining structural feature used in the classification of
various viral families.
3. From where does an enveloped virus typically acquire its lipid membrane?
A. Synthesized de novo in the cytoplasm
B. Absorbed from the surrounding environment
C. Produced by the viral ribosomes
D. Taken from the host cell’s membrane
Correct Answer: D
Expert Explanation: The viral envelope is derived from the host cell’s own plasma
membrane or internal organelles during the budding process. As the virus exits the
,host cell, it wraps itself in a portion of the host lipid bilayer. This membrane often
contains host proteins alongside viral-specific glycoproteins or spikes. The presence
of an envelope can help the virus evade the host’s immune system by mimicking
host cell surfaces. However, it also makes the virus more susceptible to
environmental stressors like heat and detergents.
4. During the bacteriophage lytic cycle, what occurs immediately after the attachment
phase?
A. Assembly
B. Uncoating
C. Release
D. Entry (Penetration)
Correct Answer: D
Expert Explanation: After a bacteriophage successfully attaches to specific
receptors on the bacterial surface, it must inject its genetic material. This process is
known as entry or penetration, where the viral DNA or RNA crosses the cell wall.
Unlike animal viruses, many bacteriophages remain outside the cell while only the
genome enters. Once the genetic material is inside, the phage can begin the process
of hijacking host resources. This transition is a critical step in initiating a productive
infection cycle.
, 5. What is the defining characteristic of the lysogenic cycle in bacteriophages?
A. Immediate lysis of the host cell
B. Rapid production of thousands of virions
C. Integration of viral DNA into the host genome
D. The virus loses its capsid during replication
Correct Answer: C
Expert Explanation: In the lysogenic cycle, the viral DNA integrates into the host’s
bacterial chromosome rather than destroying it. Once integrated, the viral DNA is
referred to as a prophage and is replicated along with the bacterial genome. This
allow the virus to persist in a dormant state through many generations of bacterial
division. Certain environmental triggers can cause the prophage to excise and enter
the lytic cycle. This strategy enables the virus to survive even when host populations
are low or conditions are unfavorable.
6. Which enzyme is used by retroviruses like HIV to convert their RNA genome into
DNA?
A. Reverse transcriptase
B. DNA ligase
C. RNA polymerase
