OpenStax Microbiology Chapter 4 Prokaryotic Diversity Test
Bank Actual Exam 2026/2027 – Complete Chapter
Assessment with Detailed Rationales | 100% Verified | Pass
Guaranteed – A+ Graded
SECTION A: PROKARYOTIC CLASSIFICATION, TAXONOMY &
PHYLOGENY (Q1–Q10)
Q1: Carl Woese's three-domain system, which separated life into Bacteria, Archaea, and
Eukarya, was established primarily by comparing:
A. Cell wall composition across species
B. Gram staining reactions of representative organisms
C. Small subunit ribosomal RNA (16S/18S rRNA) nucleotide sequences [CORRECT]
D. The types of metabolic pathways each organism uses
Correct Answer: C
Rationale: Woese used conserved rRNA sequences because they are universally
distributed and evolve slowly, revealing deep evolutionary split between the three
domains. Cell wall composition, Gram staining, and metabolism reflect phenotype and
do not reliably demonstrate ancient evolutionary relationships.
Q2: Bergey's Manual is best described as:
A. The authoritative reference work used for the identification and classification of
prokaryotes [CORRECT]
B. An atlas of viral morphology and replication strategies
C. A catalog of fungal diseases of crop plants
D. A pharmacology handbook of antimicrobial dosing
Correct Answer: A
Rationale: Bergey's Manual (Systematic and Determinative editions) is the standard
reference for bacterial taxonomy, identification, and description of prokaryotic taxa. The
other options describe virology, mycology, and pharmacology resources, not bacterial
systematics.
,Q3: A laboratory isolates a novel bacterium from a deep-sea hydrothermal vent whose
metabolism does not match any known test profile. Why is 16S rRNA gene sequencing
the preferred tool for classifying it?
A. 16S rRNA mutates so rapidly that it distinguishes every individual cell
B. Metabolic testing always produces identical results for all bacteria
C. The 16S rRNA gene is found only in human pathogens
D. 16S rRNA is universally present, functionally constrained, and slowly evolving,
allowing phylogenetic placement even when phenotypic traits are novel [CORRECT]
Correct Answer: D
Rationale: Because 16S rRNA is essential, highly conserved, and present in all
prokaryotes, sequence comparison places even unprecedented organisms within the
tree of life. Rapid mutation, universal identical metabolism, and pathogen-only
distribution are all incorrect characterizations of the gene.
Q4: On a phylogenetic tree, the point where two lineages diverge represents:
A. A horizontal gene transfer event between the two groups
B. The most recent common ancestor of the two lineages [CORRECT]
C. A mass extinction that eliminated both lineages
D. Random genetic drift within a single species
Correct Answer: B
Rationale: Branch points (nodes) mark common ancestors from which descendant
lineages split. Horizontal gene transfer can complicate tree interpretation but is not
what a divergence node depicts.
Q5: A new isolate is characterized as a Gram-negative, rod-shaped, facultative anaerobe
that ferments glucose. This approach of classifying organisms by staining, morphology,
and metabolic testing is termed:
A. Phenotypic classification [CORRECT]
B. Genotypic classification
C. Phylogenetic classification
D. Numerical taxonomy of genome sequences
Correct Answer: A
Rationale: Phenotypic classification relies on observable physical, staining, and
biochemical characteristics. Genotypic and phylogenetic methods rely on nucleic acid
comparison, and genome-based numerical taxonomy is a modern computational
extension of genotyping.
Q6: Which feature distinguishes prokaryotic cells from eukaryotic cells?
A. The presence of ribosomes for protein synthesis
B. The presence of a plasma membrane enclosing the cytoplasm
, C. The absence of a membrane-bound nucleus and other membrane-bound organelles
[CORRECT]
D. The possession of DNA as genetic material
Correct Answer: C
Rationale: Prokaryotes lack a nuclear envelope and membrane-enclosed organelles,
with their DNA located in a nucleoid region. Ribosomes, plasma membranes, and DNA
are shared by both prokaryotic and eukaryotic cells.
Q7: A student writes a report listing the intestinal bacterium as "escherichia coli" and "E.
Coli." According to the rules of binomial nomenclature, the correct format is:
A. Escherichia Coli, unitalicized
B. Escherichia coli, italicized with a capitalized genus and lowercase species [CORRECT]
C. E.coli, with the abbreviation italicized as written
D. escherichia coli, written in plain lowercase text
Correct Answer: B
Rationale: Binomial nomenclature requires the genus name capitalized, the species
epithet lowercase, and both names italicized. The other formats violate capitalization or
italicization rules.
Q8: Genes encoding antibiotic resistance are discovered in two bacterial species that,
by ribosomal RNA analysis, are only very distantly related. The best explanation is:
A. Convergent metabolism produced identical genes independently
B. Random protein folding mimicked gene transfer
C. Vertical inheritance from a single ancient ancestor alone
D. Horizontal gene transfer, which can complicate phylogenetic tree construction
[CORRECT]
Rationale: Horizontal gene transfer moves genes—especially resistance genes on
plasmids—across distant lineages, which is why trees built from single traits can be
misleading. Convergence and vertical inheritance do not produce nearly identical
resistance genes in unrelated organisms.
Q9: According to the endosymbiotic theory supported by ribosomal RNA phylogeny, the
chloroplasts of plants are most closely related to which prokaryotes?
A. Cyanobacteria [CORRECT]
B. Firmicutes
C. Spirochaetes
D. Chlamydiae
Correct Answer: A
Bank Actual Exam 2026/2027 – Complete Chapter
Assessment with Detailed Rationales | 100% Verified | Pass
Guaranteed – A+ Graded
SECTION A: PROKARYOTIC CLASSIFICATION, TAXONOMY &
PHYLOGENY (Q1–Q10)
Q1: Carl Woese's three-domain system, which separated life into Bacteria, Archaea, and
Eukarya, was established primarily by comparing:
A. Cell wall composition across species
B. Gram staining reactions of representative organisms
C. Small subunit ribosomal RNA (16S/18S rRNA) nucleotide sequences [CORRECT]
D. The types of metabolic pathways each organism uses
Correct Answer: C
Rationale: Woese used conserved rRNA sequences because they are universally
distributed and evolve slowly, revealing deep evolutionary split between the three
domains. Cell wall composition, Gram staining, and metabolism reflect phenotype and
do not reliably demonstrate ancient evolutionary relationships.
Q2: Bergey's Manual is best described as:
A. The authoritative reference work used for the identification and classification of
prokaryotes [CORRECT]
B. An atlas of viral morphology and replication strategies
C. A catalog of fungal diseases of crop plants
D. A pharmacology handbook of antimicrobial dosing
Correct Answer: A
Rationale: Bergey's Manual (Systematic and Determinative editions) is the standard
reference for bacterial taxonomy, identification, and description of prokaryotic taxa. The
other options describe virology, mycology, and pharmacology resources, not bacterial
systematics.
,Q3: A laboratory isolates a novel bacterium from a deep-sea hydrothermal vent whose
metabolism does not match any known test profile. Why is 16S rRNA gene sequencing
the preferred tool for classifying it?
A. 16S rRNA mutates so rapidly that it distinguishes every individual cell
B. Metabolic testing always produces identical results for all bacteria
C. The 16S rRNA gene is found only in human pathogens
D. 16S rRNA is universally present, functionally constrained, and slowly evolving,
allowing phylogenetic placement even when phenotypic traits are novel [CORRECT]
Correct Answer: D
Rationale: Because 16S rRNA is essential, highly conserved, and present in all
prokaryotes, sequence comparison places even unprecedented organisms within the
tree of life. Rapid mutation, universal identical metabolism, and pathogen-only
distribution are all incorrect characterizations of the gene.
Q4: On a phylogenetic tree, the point where two lineages diverge represents:
A. A horizontal gene transfer event between the two groups
B. The most recent common ancestor of the two lineages [CORRECT]
C. A mass extinction that eliminated both lineages
D. Random genetic drift within a single species
Correct Answer: B
Rationale: Branch points (nodes) mark common ancestors from which descendant
lineages split. Horizontal gene transfer can complicate tree interpretation but is not
what a divergence node depicts.
Q5: A new isolate is characterized as a Gram-negative, rod-shaped, facultative anaerobe
that ferments glucose. This approach of classifying organisms by staining, morphology,
and metabolic testing is termed:
A. Phenotypic classification [CORRECT]
B. Genotypic classification
C. Phylogenetic classification
D. Numerical taxonomy of genome sequences
Correct Answer: A
Rationale: Phenotypic classification relies on observable physical, staining, and
biochemical characteristics. Genotypic and phylogenetic methods rely on nucleic acid
comparison, and genome-based numerical taxonomy is a modern computational
extension of genotyping.
Q6: Which feature distinguishes prokaryotic cells from eukaryotic cells?
A. The presence of ribosomes for protein synthesis
B. The presence of a plasma membrane enclosing the cytoplasm
, C. The absence of a membrane-bound nucleus and other membrane-bound organelles
[CORRECT]
D. The possession of DNA as genetic material
Correct Answer: C
Rationale: Prokaryotes lack a nuclear envelope and membrane-enclosed organelles,
with their DNA located in a nucleoid region. Ribosomes, plasma membranes, and DNA
are shared by both prokaryotic and eukaryotic cells.
Q7: A student writes a report listing the intestinal bacterium as "escherichia coli" and "E.
Coli." According to the rules of binomial nomenclature, the correct format is:
A. Escherichia Coli, unitalicized
B. Escherichia coli, italicized with a capitalized genus and lowercase species [CORRECT]
C. E.coli, with the abbreviation italicized as written
D. escherichia coli, written in plain lowercase text
Correct Answer: B
Rationale: Binomial nomenclature requires the genus name capitalized, the species
epithet lowercase, and both names italicized. The other formats violate capitalization or
italicization rules.
Q8: Genes encoding antibiotic resistance are discovered in two bacterial species that,
by ribosomal RNA analysis, are only very distantly related. The best explanation is:
A. Convergent metabolism produced identical genes independently
B. Random protein folding mimicked gene transfer
C. Vertical inheritance from a single ancient ancestor alone
D. Horizontal gene transfer, which can complicate phylogenetic tree construction
[CORRECT]
Rationale: Horizontal gene transfer moves genes—especially resistance genes on
plasmids—across distant lineages, which is why trees built from single traits can be
misleading. Convergence and vertical inheritance do not produce nearly identical
resistance genes in unrelated organisms.
Q9: According to the endosymbiotic theory supported by ribosomal RNA phylogeny, the
chloroplasts of plants are most closely related to which prokaryotes?
A. Cyanobacteria [CORRECT]
B. Firmicutes
C. Spirochaetes
D. Chlamydiae
Correct Answer: A
