PCOA EXAM PRACTICE FINAL STUDY
GUIDE 2026 SOLVED QUESTIONS FULLY
CORRECT
⫸ Microbiome Answer: The collection of all microbial genomes in a
community (the total genetic content of the microbiota).
⫸ Human gut bacterial load Answer: Humans carry about 10¹⁴ bacterial
cells in the gut, roughly as many microbial cells as human cells,
weighing ~0.5 kg total.
⫸ Microbial contribution to host metabolites Answer: More than 20%
of all small-molecule metabolites circulating in human blood are
produced by gut bacteria.
⫸ Microbiome gene count vs human genes Answer: The gut
microbiome has about 100 times more genes than the human genome,
greatly expanding metabolic capabilities.
⫸ Main domains in the gut ecosystem Answer: The gut community is
mostly eubacteria (~93% of microbiome) plus the gut virome (phages),
mycobiome (yeasts like Candida), and archeome (methanogenic
archaea).
⫸ Overall diversity of the human gut microbiome Answer: Thousands
of commensal bacterial species exist globally, but each individual
,typically harbors only a few hundred species, often with multiple strains
of each.
⫸ Major bacterial phyla in the human gut Answer: The dominant phyla
are Firmicutes (Gram+), Bacteroidetes (Gram−), Actinobacteria
(Gram+), Proteobacteria (Gram−), and Verrucomicrobiota (includes
Akkermansia).
⫸ Typical location of gut microbiota along the GI tract Answer: Most
gut bacteria live in the anaerobic large intestine/colon, where oxygen is
lowest and fermentation dominates.
⫸ Cecum in hindgut-fermenting herbivores Answer: In hindgut
fermenters (e.g., horses, rabbits), most gut bacteria are in a large,
fermentation-focused cecum, an enlarged version of the human
appendix.
⫸ 16S rRNA gene sequencing - basic idea Answer: Amplify and
sequence the 16S rRNA gene (present in all bacteria, with conserved and
variable regions) from a community to identify which bacterial taxa are
present.
⫸ Conserved vs variable regions in 16S rRNA Answer: Conserved
regions allow universal primers to bind many species, while variable
regions differ between species and provide taxonomic discrimination.
,⫸ Relative abundance from 16S data Answer: The proportion of reads
assigned to a given 16S sequence (ASV) reflects that taxon's relative
abundance in the community sample.
⫸ Amplicon Sequence Variants (ASVs) Answer: Clusters of nearly
identical 16S sequences that are treated as species- or strain-level
operational units when analyzing microbiota composition.
⫸ Limitation of 16S rRNA profiling Answer: 16S sequencing typically
cannot resolve beyond the genus level and has limited ability to
distinguish closely related species or strains.
⫸ Shotgun metagenomic sequencing - definition Answer: Randomly
sequences all DNA extracted from a microbiome sample, allowing
simultaneous determination of taxonomic composition and functional
gene content.
⫸ Advantages of shotgun metagenomics Answer: Can achieve species-
and sometimes strain-level resolution, count hits to specific genes or
pathways, and assemble metagenome-assembled genomes (MAGs) of
dominant microbes.
⫸ Where do human babies get their gut bacteria? Answer: Newborns
acquire microbes from their mothers (gut, vaginal, skin, oral
microbiota), from the environment (hospital, home), from breast milk,
and later from solid foods.
, ⫸ Baby vs mother gut microbiome diversity Answer: Mothers have
high, stable species richness; babies start with much lower diversity and
fewer species, then increase in richness over the first 2-3 years of life.
⫸ Development of characteristic infant gut microbiota Answer: Within
the first year, infants develop a characteristic gut community dominated
by Firmicutes and Bacteroidetes, approaching an "adult-like"
composition.
⫸ Maternal strain transmission to infants Answer: Infants receive a
mixture of maternal strains from different body sites, but maternal gut
strains (especially Bifidobacterium and Bacteroides) are more persistent
in the baby than non-maternal strains.
⫸ Key finding about reproducibly transmitted maternal strains Answer:
Studies have identified a core set (around a few dozen) of maternal
species/strains that reproducibly colonize infants, many belonging to
Bifidobacterium and Bacteroides genera.
⫸ Effect of Caesarean section on early gut microbiota Answer: C-
section-delivered infants tend to have fewer beneficial Bifidobacterium
and Bacteroides and more hospital-associated opportunistic pathogens
such as Klebsiella and Enterobacter in early life.
⫸ Impact of C-section on mother-to-baby transmission Answer: C-
section disrupts direct vertical transmission of many maternal gut
strains, leading to lower rates of early transfer compared to vaginal birth.
GUIDE 2026 SOLVED QUESTIONS FULLY
CORRECT
⫸ Microbiome Answer: The collection of all microbial genomes in a
community (the total genetic content of the microbiota).
⫸ Human gut bacterial load Answer: Humans carry about 10¹⁴ bacterial
cells in the gut, roughly as many microbial cells as human cells,
weighing ~0.5 kg total.
⫸ Microbial contribution to host metabolites Answer: More than 20%
of all small-molecule metabolites circulating in human blood are
produced by gut bacteria.
⫸ Microbiome gene count vs human genes Answer: The gut
microbiome has about 100 times more genes than the human genome,
greatly expanding metabolic capabilities.
⫸ Main domains in the gut ecosystem Answer: The gut community is
mostly eubacteria (~93% of microbiome) plus the gut virome (phages),
mycobiome (yeasts like Candida), and archeome (methanogenic
archaea).
⫸ Overall diversity of the human gut microbiome Answer: Thousands
of commensal bacterial species exist globally, but each individual
,typically harbors only a few hundred species, often with multiple strains
of each.
⫸ Major bacterial phyla in the human gut Answer: The dominant phyla
are Firmicutes (Gram+), Bacteroidetes (Gram−), Actinobacteria
(Gram+), Proteobacteria (Gram−), and Verrucomicrobiota (includes
Akkermansia).
⫸ Typical location of gut microbiota along the GI tract Answer: Most
gut bacteria live in the anaerobic large intestine/colon, where oxygen is
lowest and fermentation dominates.
⫸ Cecum in hindgut-fermenting herbivores Answer: In hindgut
fermenters (e.g., horses, rabbits), most gut bacteria are in a large,
fermentation-focused cecum, an enlarged version of the human
appendix.
⫸ 16S rRNA gene sequencing - basic idea Answer: Amplify and
sequence the 16S rRNA gene (present in all bacteria, with conserved and
variable regions) from a community to identify which bacterial taxa are
present.
⫸ Conserved vs variable regions in 16S rRNA Answer: Conserved
regions allow universal primers to bind many species, while variable
regions differ between species and provide taxonomic discrimination.
,⫸ Relative abundance from 16S data Answer: The proportion of reads
assigned to a given 16S sequence (ASV) reflects that taxon's relative
abundance in the community sample.
⫸ Amplicon Sequence Variants (ASVs) Answer: Clusters of nearly
identical 16S sequences that are treated as species- or strain-level
operational units when analyzing microbiota composition.
⫸ Limitation of 16S rRNA profiling Answer: 16S sequencing typically
cannot resolve beyond the genus level and has limited ability to
distinguish closely related species or strains.
⫸ Shotgun metagenomic sequencing - definition Answer: Randomly
sequences all DNA extracted from a microbiome sample, allowing
simultaneous determination of taxonomic composition and functional
gene content.
⫸ Advantages of shotgun metagenomics Answer: Can achieve species-
and sometimes strain-level resolution, count hits to specific genes or
pathways, and assemble metagenome-assembled genomes (MAGs) of
dominant microbes.
⫸ Where do human babies get their gut bacteria? Answer: Newborns
acquire microbes from their mothers (gut, vaginal, skin, oral
microbiota), from the environment (hospital, home), from breast milk,
and later from solid foods.
, ⫸ Baby vs mother gut microbiome diversity Answer: Mothers have
high, stable species richness; babies start with much lower diversity and
fewer species, then increase in richness over the first 2-3 years of life.
⫸ Development of characteristic infant gut microbiota Answer: Within
the first year, infants develop a characteristic gut community dominated
by Firmicutes and Bacteroidetes, approaching an "adult-like"
composition.
⫸ Maternal strain transmission to infants Answer: Infants receive a
mixture of maternal strains from different body sites, but maternal gut
strains (especially Bifidobacterium and Bacteroides) are more persistent
in the baby than non-maternal strains.
⫸ Key finding about reproducibly transmitted maternal strains Answer:
Studies have identified a core set (around a few dozen) of maternal
species/strains that reproducibly colonize infants, many belonging to
Bifidobacterium and Bacteroides genera.
⫸ Effect of Caesarean section on early gut microbiota Answer: C-
section-delivered infants tend to have fewer beneficial Bifidobacterium
and Bacteroides and more hospital-associated opportunistic pathogens
such as Klebsiella and Enterobacter in early life.
⫸ Impact of C-section on mother-to-baby transmission Answer: C-
section disrupts direct vertical transmission of many maternal gut
strains, leading to lower rates of early transfer compared to vaginal birth.
