OpenStax Microbiology Chapter 5 The Eukaryotes of
Microbiology Test Bank Actual Exam 2026/2027 – Complete
50 Questions with Detailed Rationales | 100% Verified | Pass
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Section A: Eukaryotic Cell Structure & Function
Q1: During microscopy of a newly isolated pond microbe, which finding would
definitively identify it as a eukaryote rather than a prokaryote?
A. Presence of ribosomes for protein synthesis
B. A plasma membrane enclosing the cytoplasm
C. A true nucleus enclosed within a nuclear envelope containing chromatin [CORRECT]
D. Genetic material composed of DNA
Correct Answer: C
Rationale: A membrane-bound nucleus is the defining feature of eukaryotic cells.
Ribosomes, a plasma membrane, and DNA are present in both prokaryotes and
eukaryotes, so they cannot distinguish the two.
Q2: A student observes a protozoan containing membrane-bound vesicles filled with
digestive enzymes that break down engulfed food particles and bacteria. These
organelles are:
A. Lysosomes [CORRECT]
B. Ribosomes
C. Mitochondria
D. Nucleoli
Correct Answer: A
Rationale: Lysosomes are membrane-bound sacs of hydrolytic digestive enzymes used
in intracellular digestion and phagocytosis. Mitochondria produce ATP, ribosomes
synthesize protein, and nucleoli assemble ribosomal subunits—none perform enzymatic
digestion.
Q3: A laboratory is comparing bacterial and eukaryotic cells under an ultracentrifugation
study. The sedimentation coefficient expected for eukaryotic cytoplasmic ribosomes is:
A. 70S
B. 80S [CORRECT]
,C. 50S
D. 30S
Correct Answer: B
Rationale: Eukaryotic ribosomes are 80S (60S + 40S subunits), whereas prokaryotic
ribosomes are 70S (50S + 30S subunits). The 50S and 30S values are prokaryotic
subunits, not whole eukaryotic ribosomes.
Q4: A unicellular eukaryote specializing in the synthesis and export of large quantities of
protein would be expected to have abundant:
A. Smooth endoplasmic reticulum
B. Peroxisomes
C. Lysosomes
D. Rough endoplasmic reticulum studded with ribosomes [CORRECT]
Correct Answer: D
Rationale: Rough ER is covered with ribosomes and is the site of protein synthesis for
secretion or membrane insertion. Smooth ER handles lipid synthesis and detoxification,
while peroxisomes and lysosomes perform oxidative and digestive functions,
respectively.
Q5: After synthesis in the endoplasmic reticulum, proteins are chemically modified,
sorted, and packaged into secretory vesicles by the:
A. Nucleolus
B. Lysosome
C. Golgi apparatus [CORRECT]
D. Cytoskeleton
Correct Answer: C
Rationale: The Golgi apparatus modifies, tags, sorts, and packages ER products into
vesicles for delivery. The nucleolus makes rRNA, lysosomes digest material, and the
cytoskeleton provides structural support and transport tracks.
Q6: Which observation provides the strongest evidence supporting the endosymbiotic
theory of mitochondrial origin?
A. Mitochondria contain linear chromosomes wrapped around histones
B. Mitochondria synthesize peptidoglycan in their membranes
C. Mitochondria possess their own circular DNA and 70S ribosomes and divide by
binary fission, resembling bacteria [CORRECT]
D. Mitochondria lack a double membrane
Correct Answer: C
, Rationale: Circular DNA, 70S ribosomes, and binary fission are bacterial traits retained
by mitochondria, supporting descent from an ancestral aerobic bacterium. The other
statements are factually incorrect about mitochondrial structure.
Q7: Which eukaryotic microbial group generally LACKS a cell wall?
A. Fungi
B. Protozoa [CORRECT]
C. Algae
D. Plants
Correct Answer: B
Rationale: Protozoa typically lack cell walls (some possess only a flexible pellicle),
which allows amoeboid flexibility. Fungi have chitin walls, and algae and plants
characteristically have cellulose-based walls.
Q8: The cytoskeletal elements composed of tubulin that form the mitotic spindle and
constitute eukaryotic cilia and flagella are:
A. Microfilaments (actin)
B. Microtubules [CORRECT]
C. Intermediate filaments
D. Peptidoglycan strands
Correct Answer: B
Rationale: Microtubules are tubulin polymers that form mitotic spindles and the 9+2
arrangement of cilia and flagella. Actin microfilaments drive amoeboid movement and
cytokinesis, intermediate filaments provide tensile strength, and peptidoglycan is
prokaryotic.
Q9: In eukaryotic cells, DNA wraps around histone proteins to form:
A. Plasmids
B. Nucleoids
C. Chromatin organized into nucleosomes [CORRECT]
D. Glycocalyces
Correct Answer: C
Rationale: Histone-bound DNA coils into nucleosomes, producing chromatin within the
nucleus. Plasmids and nucleoids describe prokaryotic DNA organization, and
glycocalyces are extracellular carbohydrate layers.
Q10: A researcher studying a free-living protozoan identifies vesicles containing
catalase that break down hydrogen peroxide generated during oxidative metabolism.
These organelles are:
A. Golgi apparatus
Microbiology Test Bank Actual Exam 2026/2027 – Complete
50 Questions with Detailed Rationales | 100% Verified | Pass
Guaranteed – A+ Graded
Section A: Eukaryotic Cell Structure & Function
Q1: During microscopy of a newly isolated pond microbe, which finding would
definitively identify it as a eukaryote rather than a prokaryote?
A. Presence of ribosomes for protein synthesis
B. A plasma membrane enclosing the cytoplasm
C. A true nucleus enclosed within a nuclear envelope containing chromatin [CORRECT]
D. Genetic material composed of DNA
Correct Answer: C
Rationale: A membrane-bound nucleus is the defining feature of eukaryotic cells.
Ribosomes, a plasma membrane, and DNA are present in both prokaryotes and
eukaryotes, so they cannot distinguish the two.
Q2: A student observes a protozoan containing membrane-bound vesicles filled with
digestive enzymes that break down engulfed food particles and bacteria. These
organelles are:
A. Lysosomes [CORRECT]
B. Ribosomes
C. Mitochondria
D. Nucleoli
Correct Answer: A
Rationale: Lysosomes are membrane-bound sacs of hydrolytic digestive enzymes used
in intracellular digestion and phagocytosis. Mitochondria produce ATP, ribosomes
synthesize protein, and nucleoli assemble ribosomal subunits—none perform enzymatic
digestion.
Q3: A laboratory is comparing bacterial and eukaryotic cells under an ultracentrifugation
study. The sedimentation coefficient expected for eukaryotic cytoplasmic ribosomes is:
A. 70S
B. 80S [CORRECT]
,C. 50S
D. 30S
Correct Answer: B
Rationale: Eukaryotic ribosomes are 80S (60S + 40S subunits), whereas prokaryotic
ribosomes are 70S (50S + 30S subunits). The 50S and 30S values are prokaryotic
subunits, not whole eukaryotic ribosomes.
Q4: A unicellular eukaryote specializing in the synthesis and export of large quantities of
protein would be expected to have abundant:
A. Smooth endoplasmic reticulum
B. Peroxisomes
C. Lysosomes
D. Rough endoplasmic reticulum studded with ribosomes [CORRECT]
Correct Answer: D
Rationale: Rough ER is covered with ribosomes and is the site of protein synthesis for
secretion or membrane insertion. Smooth ER handles lipid synthesis and detoxification,
while peroxisomes and lysosomes perform oxidative and digestive functions,
respectively.
Q5: After synthesis in the endoplasmic reticulum, proteins are chemically modified,
sorted, and packaged into secretory vesicles by the:
A. Nucleolus
B. Lysosome
C. Golgi apparatus [CORRECT]
D. Cytoskeleton
Correct Answer: C
Rationale: The Golgi apparatus modifies, tags, sorts, and packages ER products into
vesicles for delivery. The nucleolus makes rRNA, lysosomes digest material, and the
cytoskeleton provides structural support and transport tracks.
Q6: Which observation provides the strongest evidence supporting the endosymbiotic
theory of mitochondrial origin?
A. Mitochondria contain linear chromosomes wrapped around histones
B. Mitochondria synthesize peptidoglycan in their membranes
C. Mitochondria possess their own circular DNA and 70S ribosomes and divide by
binary fission, resembling bacteria [CORRECT]
D. Mitochondria lack a double membrane
Correct Answer: C
, Rationale: Circular DNA, 70S ribosomes, and binary fission are bacterial traits retained
by mitochondria, supporting descent from an ancestral aerobic bacterium. The other
statements are factually incorrect about mitochondrial structure.
Q7: Which eukaryotic microbial group generally LACKS a cell wall?
A. Fungi
B. Protozoa [CORRECT]
C. Algae
D. Plants
Correct Answer: B
Rationale: Protozoa typically lack cell walls (some possess only a flexible pellicle),
which allows amoeboid flexibility. Fungi have chitin walls, and algae and plants
characteristically have cellulose-based walls.
Q8: The cytoskeletal elements composed of tubulin that form the mitotic spindle and
constitute eukaryotic cilia and flagella are:
A. Microfilaments (actin)
B. Microtubules [CORRECT]
C. Intermediate filaments
D. Peptidoglycan strands
Correct Answer: B
Rationale: Microtubules are tubulin polymers that form mitotic spindles and the 9+2
arrangement of cilia and flagella. Actin microfilaments drive amoeboid movement and
cytokinesis, intermediate filaments provide tensile strength, and peptidoglycan is
prokaryotic.
Q9: In eukaryotic cells, DNA wraps around histone proteins to form:
A. Plasmids
B. Nucleoids
C. Chromatin organized into nucleosomes [CORRECT]
D. Glycocalyces
Correct Answer: C
Rationale: Histone-bound DNA coils into nucleosomes, producing chromatin within the
nucleus. Plasmids and nucleoids describe prokaryotic DNA organization, and
glycocalyces are extracellular carbohydrate layers.
Q10: A researcher studying a free-living protozoan identifies vesicles containing
catalase that break down hydrogen peroxide generated during oxidative metabolism.
These organelles are:
A. Golgi apparatus
