C13 Sample Questions from Brock

Question 1

The earliest stromatolites were probably formed by
A) anoxygenic phototrophs.
B) anoxygenic lithotrophs.
C) oxygenic phototrophs.
D) oxygenic lithotrophs.

Answer 1

A) anoxygenic phototrophs.

Early Earth lacked free oxygen, so the first stromatolites were likely formed by anoxygenic photosynthetic microorganisms.

Question 2

What two gases were most abundant on early Earth?
A) O2 and CO2
B) N2 and H2
C) CO2 and H2
D) CO2 and N2

Answer 2

D) CO2 and N2.

Early Earth’s atmosphere was rich in carbon dioxide and nitrogen gas.

Question 3

The earliest RNA probably functioned in
A) catalysis.
B) self-replication.
C) both catalysis and self-replication.
D) neither catalysis nor self-replication.

Answer 3

C) both catalysis and self-replication.

The RNA world hypothesis proposes that early life relied on RNA for both catalytic and genetic functions.

Question 4

Evolution is driven by
A) random mutation.
B) novel metabolic pathways.
C) selection pressure.
D) selection pressure applied to random mutation.

Answer 4

D) selection pressure applied to random mutation.

Evolution occurs through the selection of advantageous mutations that arise randomly.

Question 5

Which of the following is an assumption used in the molecular clock approach?
A) Nucleotide changes accumulate in a sequence in proportion to time.
B) Nucleotide changes are generally NOT transferred to progeny.
C) Nucleotide changes are NOT random.
D) Nucleotide changes are subject to intense selective pressure.

Answer 5

A) Nucleotide changes accumulate in a sequence in proportion to time.

This is the fundamental assumption of the molecular clock approach.

Question 6

A monophyletic group is a group that
A) descended from one ancestor.
B) has the same fitness level.
C) possesses one taxonomic trait that is the same.
D) shares one phylogenetic marker.

Answer 6

A) descended from one ancestor.

A monophyletic group includes a common ancestor and all of its descendants.

Question 7

Horizontal gene transfer
A) is so rare over evolutionary history that it is not considered when examining microbial evolution.
B) occurs within bacterial species.
C) complicates the construction of phylogenetic trees and the interpretation of specific traits in relation to evolution.
D) only affects the evolution of plasmids.

Answer 7

C) complicates the construction of phylogenetic trees and the interpretation of specific traits in relation to evolution. Horizontal gene transfer can make it difficult to trace evolutionary relationships.

Question 8

Molecular sequencing suggests that mitochondria arose from a group of prokaryotic organisms within the
A) Thermoproteota.
B) cyanobacteria.
C) iron-oxidizing bacteria.
D) Alphaproteobacteria.

Answer 8

D) Alphaproteobacteria.

Evidence suggests that mitochondria evolved from an endosymbiotic alphaproteobacterium.

Question 9

Which statement most closely expresses our present understanding?
A) The chloroplast is an ancestor of the cyanobacteria.
B) The cyanobacteria are descendants of the chloroplast.
C) The chloroplast arose from the incorporation of a cyanobacterial-like organism.
D) The chloroplast and the cyanobacteria are not closely (or specifically) related.

Answer 9

C) The chloroplast arose from the incorporation of a cyanobacterial-like organism.

Chloroplasts are thought to have originated from an endosymbiotic cyanobacterium.

Question 10

Two tubes are inoculated from the same tube containing a bacterial culture. The cultures are then transferred every day for 2 months. All of the media and growth conditions are the same in every tube. After 2 months of cultivation, the fitness and genotype frequencies of the populations in the two tubes are compared. The fitness of the two cultures is the same, but the genotype frequencies are very different in the two cultures. How is this possible?
A) Two months is not long enough for different fitness levels to evolve even if the genotype frequencies change.
B) This result is not possible because different genotype frequencies would result in different fitness levels under the same growth conditions.
C) Natural selection caused the evolution of different genotype frequencies within the separate test tubes.
D) Genetic drift within the small populations in the test tubes resulted in different genotype frequencies.

Answer 10

D) Genetic drift within the small populations in the test tubes resulted in different genotype frequencies.

Genetic drift, the random fluctuation of gene frequencies, is more pronounced in small populations.

Question 11

If you allowed 10 identical parallel Salmonella cultures to evolve for 10,000 generations under new growth conditions with very little nitrogen, the parallel cultures would
A) evolve identical adaptations to use the nitrogen source provided in the media.
B) not change or adapt very much over this small number of generations.
C) each accumulate different random mutations resulting in different adaptations to use the nitrogen in the media.
D) direct mutations to occur in nitrogen utilization and uptake genes in order to adapt rapidly to the culture conditions.

Answer 11

C) each accumulate different random mutations resulting in different adaptations to use the nitrogen in the media.

While there’s selective pressure to utilize nitrogen, mutations are random. Parallel cultures will experience different mutations, leading to diverse adaptations even under the same conditions.

Question 12

Ribotyping
A) bypasses sequencing and sequence alignments.
B) exploits unique DNA restriction patterns.
C) allows discrimination between species and different strains of a species.
D) bypasses sequencing and sequence alignments, exploits unique DNA restriction patterns, and allows discrimination between species and different strains of a species.

Answer 12

D) bypasses sequencing and sequence alignments, exploits unique DNA restriction patterns, and allows discrimination between species and different strains of a species.

Ribotyping analyzes differences in rRNA genes by examining restriction fragment length polymorphisms (RFLPs). This avoids direct sequencing but still provides strain-level differentiation.

Question 13

It is believed that phototrophy arose approximately 3.3 billion years ago in
A) Bacteria.
B) Archaea.
C) Eukarya.
D) LUCA.

Answer 13

A) Bacteria.

Evidence suggests anoxygenic photosynthesis first evolved in bacteria before the evolution of oxygenic photosynthesis in cyanobacteria.

Question 14

You are studying 12 new isolates from the human skin. Their average nucleotide identity for shared orthologous genes is 97%.The isolates would most likely be
A) classified as individual strains of the same species.
B) classified as individual species of the same genus.
C) split into different families.
D) classified as the same species if they can mate via conjugation.

Answer 14

A) classified as individual strains of the same species.

An ANI of 97% or greater is typically considered the threshold for defining bacterial species.

Question 15

Microbial _______ studies the diversity of microorganisms and links their phylogeny with ______.
A) taxonomy / genotype
B) phylogeny / phenotype
C) taxonomy / phenotype
D) systematics / taxonomy

Answer 15

D) systematics / taxonomy

Question 16

The earliest photosynthetic microbes, before the cyanobacterial lineage developed, oxidized substances other than water. What was produced by these microbes instead of oxygen?
A) nitrate
B) elemental sulfur
C) ferrous iron
D) hydrogen sulfide

Answer 16

B) elemental sulfur.

Anoxygenic photosynthesis uses electron donors other than water, such as H2S, resulting in the production of elemental sulfur rather than oxygen.

Question 17

Two eukaryotic organelles that are hypothesized to be the result of endosymbiosis are the ______ and the _____.
A) nucleus / Golgi body
B) mitochondrion / chloroplast
C) endoplasmic reticulum / Golgi body
D) hydrogenosome / chloroplast

Answer 17

B) mitochondrion / chloroplast.

The endosymbiotic theory proposes these organelles originated from bacteria engulfed by a host cell.

Question 18

What characteristics make a gene a good candidate for determining the evolutionary relationships between organisms?
A) highly conserved
B) universally distributed
C) transferred horizontally between species
D) highly conserved and universally distributed

Answer 18

D) highly conserved and universally distributed.

Genes used for phylogenetic analysis should be present in all organisms being compared (universally distributed) and change slowly over time (highly conserved).

Question 19

The first catalytic and self-replication biological molecule was most likely
A) RNA.
B) DNA.
C) proteins.
D) ATP.

Answer 19

A) RNA.

The RNA world hypothesis posits that RNA, with its catalytic and self-replicating properties, preceded DNA and proteins as the primary biological molecule.

Question 20

The evolutionary history of a group of organisms is called its ______ and it is inferred from _________.
A) taxonomy / phenotype
B) phylogeny / nucleotide sequence data
C) phylogeny / phenotype
D) taxonomy / morphology

Answer 20

B) phylogeny / nucleotide sequence data.

Phylogeny is the evolutionary history, often inferred from comparing DNA or RNA sequences.

Question 21

Systematic analysis now commonly includes to identify, characterize, and determine relationships between new strains of bacterial species.
A) whole genome analysis
B) microscopy
C) staining
D) pigments

Answer 21

A) whole genome analysis.

Whole genome sequencing provides the most comprehensive data for identifying and characterizing bacterial strains.

Question 22

T/F: The atmosphere of primitive Earth is usually described as an oxidizing atmosphere.

Answer 22

False. Primitive Earth had a reducing atmosphere, not an oxidizing one.

Question 23

T/F: The establishment of DNA as the genome of the cell may have resulted from the need to store genetic information in a more stable form than RNA.

Answer 23

True. DNA is more stable than RNA, offering a selective advantage for information storage.

Question 24

T/F: Eukaryotes originated after the rise in atmospheric oxygen.

Answer 24

True. Eukaryotes arose after oxygenic photosynthesis by cyanobacteria increased atmospheric oxygen levels.

Question 25

T/F: Molecular phylogeny and rRNA analysis provided the evidence used to separate Bacteria and Archaea into distinct domains.

Answer 25

True. rRNA analysis was key to recognizing Bacteria and Archaea as distinct domains.

Question 26

T/F: Organisms with greater phylogenetic distance in their genomes have less gene exchange than those with less phylogenetic distance.

Answer 26

True. Greater phylogenetic distance implies less frequent gene exchange.

Question 27

T/F: Microbial species are difficult to define because they are seldom monophyletic.

Answer 27

True. Microbial species are often not monophyletic due to horizontal gene transfer.

Question 28

T/F: Organisms within a species should have strong phenotypic cohesiveness.

Answer 28

True. Members of a species should share significant phenotypic similarities.

Question 29

T/F: At present there are four phyla in the domain Bacteria.

Answer 29

False. There are many more than four phyla in the domain Bacteria.

Question 30

T/F: One phenotypic trait used for species identification and description is the analysis of the types and proportions of the fatty acids present in the cytoplasmic and outer membranes. The methodology employed is often nicknamed FAME.

Answer 30

True. Fatty acid methyl ester analysis (FAME) is a phenotypic method used for microbial identification.

Question 31

T/F: Oxygen was a driving factor in the formation of eukaryotic cells.

Answer 31

True. Oxygen played a crucial role in the development of eukaryotic cells, particularly in the endosymbiotic origin of mitochondria.

Question 32

T/F: Horizontal gene transfer is one plausible explanation as to why organisms in Archaea, Bacteria, and Eukarya still share so many genes among such distinct domains.

Answer 32

True. Horizontal gene transfer can explain shared genes across domains despite their divergence.