BIOD 171 Microbiology Module 6 Exam
Portage Learning 2026/2027 | Immunology
Questions and Answers with Rationales
Guaranteed Pass (GRADED A+)
Question 1
Which statement correctly describes the structural
classification of viruses?
A) Viruses are prokaryotic because they lack a membrane-
bound nucleus.
B) Viruses are eukaryotic because their genome is enclosed
within a capsid.
C) Viruses are neither prokaryotic nor eukaryotic because
they are acellular.
D) Viruses are classified as archaea due to their ability to
survive harsh conditions.
*Correct Answer: C) Viruses are neither prokaryotic nor
eukaryotic because they are acellular. *
Rationale: Viruses lack cellular structure entirely—no
ribosomes, no cytoplasm, no plasma membrane, and no
independent metabolism. The capsid enclosing the viral
genome is a protein shell, not a nucleus, and does not
confer eukaryotic status. Viruses are therefore classified as
,acellular infectious agents outside the three domains of
cellular life .
Question 2
A virologist isolates an infectious particle consisting of a
single-stranded RNA genome surrounded by a protein
capsid, with no outer lipid membrane. How should this
virus be classified?
A) Enveloped DNA virus
B) Non-enveloped RNA virus
C) Enveloped RNA virus
D) Prokaryotic RNA pathogen
*Correct Answer: B) Non-enveloped RNA virus *
Rationale: The presence of an RNA genome and a protein
capsid without a surrounding lipid bilayer defines a non-
enveloped (naked) RNA virus. The absence of an envelope is
a key structural distinction that affects stability,
transmission, and disinfection susceptibility .
Question 3
,Which statement best describes the viral envelope?
A) A peptidoglycan layer synthesized entirely by the virus.
B) A protein shell that surrounds the viral genome in all
viruses.
C) A lipid bilayer derived from host membranes and
containing viral glycoproteins.
D) A rigid outer capsid present only in bacteriophages.
*Correct Answer: C) A lipid bilayer derived from host
membranes and containing viral glycoproteins. *
Rationale: Enveloped viruses acquire their lipid membrane
from host cell membranes during budding. This envelope is
embedded with viral glycoproteins that are critical for host
cell recognition and entry. Importantly, not all viruses
possess an envelope—non-enveloped viruses lack this
structure entirely .
Question 4
You would expect to see a viral envelope on a virus
infecting which type of host?
A) A bacterial cell
B) A plant cell
, C) An animal cell
D) A fungal spore
*Correct Answer: C) An animal cell *
Rationale: The overwhelming majority of animal viruses are
enveloped. In contrast, most bacteriophages (viruses
infecting bacteria) and plant viruses are non-enveloped, as
the rigid cell walls of these hosts complicate the budding
process required for envelope acquisition .
Question 5
Rank the following viruses from largest to smallest:
Variolavirus (~200 nm), Orthomyxovirus (100–150 nm),
Poliovirus (~30 nm).
A) Poliovirus > Orthomyxovirus > Variolavirus
B) Variolavirus > Orthomyxovirus > Poliovirus
C) Orthomyxovirus > Poliovirus > Variolavirus
D) Poliovirus > Variolavirus > Orthomyxovirus
*Correct Answer: B) Variolavirus > Orthomyxovirus >
Poliovirus *
Rationale: Variolavirus (smallpox) is among the largest and
most complex DNA viruses at approximately 200 nm.
Orthomyxoviruses (influenza viruses) are intermediate-sized
Portage Learning 2026/2027 | Immunology
Questions and Answers with Rationales
Guaranteed Pass (GRADED A+)
Question 1
Which statement correctly describes the structural
classification of viruses?
A) Viruses are prokaryotic because they lack a membrane-
bound nucleus.
B) Viruses are eukaryotic because their genome is enclosed
within a capsid.
C) Viruses are neither prokaryotic nor eukaryotic because
they are acellular.
D) Viruses are classified as archaea due to their ability to
survive harsh conditions.
*Correct Answer: C) Viruses are neither prokaryotic nor
eukaryotic because they are acellular. *
Rationale: Viruses lack cellular structure entirely—no
ribosomes, no cytoplasm, no plasma membrane, and no
independent metabolism. The capsid enclosing the viral
genome is a protein shell, not a nucleus, and does not
confer eukaryotic status. Viruses are therefore classified as
,acellular infectious agents outside the three domains of
cellular life .
Question 2
A virologist isolates an infectious particle consisting of a
single-stranded RNA genome surrounded by a protein
capsid, with no outer lipid membrane. How should this
virus be classified?
A) Enveloped DNA virus
B) Non-enveloped RNA virus
C) Enveloped RNA virus
D) Prokaryotic RNA pathogen
*Correct Answer: B) Non-enveloped RNA virus *
Rationale: The presence of an RNA genome and a protein
capsid without a surrounding lipid bilayer defines a non-
enveloped (naked) RNA virus. The absence of an envelope is
a key structural distinction that affects stability,
transmission, and disinfection susceptibility .
Question 3
,Which statement best describes the viral envelope?
A) A peptidoglycan layer synthesized entirely by the virus.
B) A protein shell that surrounds the viral genome in all
viruses.
C) A lipid bilayer derived from host membranes and
containing viral glycoproteins.
D) A rigid outer capsid present only in bacteriophages.
*Correct Answer: C) A lipid bilayer derived from host
membranes and containing viral glycoproteins. *
Rationale: Enveloped viruses acquire their lipid membrane
from host cell membranes during budding. This envelope is
embedded with viral glycoproteins that are critical for host
cell recognition and entry. Importantly, not all viruses
possess an envelope—non-enveloped viruses lack this
structure entirely .
Question 4
You would expect to see a viral envelope on a virus
infecting which type of host?
A) A bacterial cell
B) A plant cell
, C) An animal cell
D) A fungal spore
*Correct Answer: C) An animal cell *
Rationale: The overwhelming majority of animal viruses are
enveloped. In contrast, most bacteriophages (viruses
infecting bacteria) and plant viruses are non-enveloped, as
the rigid cell walls of these hosts complicate the budding
process required for envelope acquisition .
Question 5
Rank the following viruses from largest to smallest:
Variolavirus (~200 nm), Orthomyxovirus (100–150 nm),
Poliovirus (~30 nm).
A) Poliovirus > Orthomyxovirus > Variolavirus
B) Variolavirus > Orthomyxovirus > Poliovirus
C) Orthomyxovirus > Poliovirus > Variolavirus
D) Poliovirus > Variolavirus > Orthomyxovirus
*Correct Answer: B) Variolavirus > Orthomyxovirus >
Poliovirus *
Rationale: Variolavirus (smallpox) is among the largest and
most complex DNA viruses at approximately 200 nm.
Orthomyxoviruses (influenza viruses) are intermediate-sized
