Chapter 17

Defining bacterial species currently relies on __________ as these provide the best measures of similarity and divergence. Select one: a. DNA relatedness and sharing of ecological niche b. DNA relatedness and capacity of horizontal gene transfer c. morphological traits and lifestyle d. DNA relatedness and RNA relatedness

a. DNA relatedness and sharing of ecological niche CorrectFEEDBACK: Phylogenetic relatedness and ecotype are used to define species, where individuals with 95% or greater similarity in SSU rRNA and 95% or greater common habitat and metabolism are the same species. This allows phylogeny and ecology to be reconciled though it is still not a perfect system.

One reason why RNA molecules are the leading candidate as the first informational molecule is that Select one: a. some RNA molecules can function as enzymes. b. RNA nucleotides are a major component of cell membranes. c. RNA molecules are usually double stranded. d. RNA serves as the hereditary material in today's prokaryotic cells.

a. some RNA molecules can function as enzymes. Correct FEEDBACK: RNAs are proposed as an early informational molecule because they can serve as both information carriers and catalysts. Even in present time, there are some ribozymes, that is, enzymes whose catalytic activity depends on RNA and not on amino acids.

The metabolist model attempts to explain Select one: a. the origin of biosynthesis on the basis of CO2 fixation. b. how the first cells became encapsulated by lipid membranes. c. how the first nucleic acids formed. d. how DNA became the hereditary material.

a. the origin of biosynthesis on the basis of CO2 fixation. Correct FEEDBACK: The metabolist theory aims to postulate a model of how simple inorganic reactions led to complex biochemical cycles producing complex biopolymers such as nucleic acids and proteins

Organisms acquire DNA Select one: a. via horizontal transmission from cells of any domain, and also from vertical transmission. b. only from their parent cell via vertical transmission. c. via horizontal transmission, but only from cells of the same domain, and also from vertical transmission. d. via horizontal transmission, but only from cells of the same species, and also from vertical transmission.

a. via horizontal transmission from cells of any domain, and also from vertical transmission. Correct FEEDBACK: Horizontal transmission can cross domain barriers (e.g., mitochondria, genes from thermophilic archaea transferred to thermophilic bacteria).

What do eukaryotes and archaea have in common that is lacking from bacteria? Select one: a. A membrane surrounding the genetic material b. Splicing machinery for introns c. The presence of ribosomes d. Unique membrane lipids in the cell membrane

b. Splicing machinery for introns Correct FEEDBACK: Bacteria lack introns in their DNA. Both archaea and bacteria are prokaryotes and all three domains possess ribosomes. Only the archaeal membrane lipids have unique ether links.

A clade is Select one: a. a family of extinct organisms. b. a group of organisms that share a common ancestor not shared by other organisms. c. a group of organisms that are similar in size and shape (morphology). d. another name for a paraphyletic group.

b. a group of organisms that share a common ancestor not shared by other organisms. Correct FEEDBACK: A clade is a monophyletic group, that is, a group whose members share a common ancestor not shared by any group outside the clade.

Symbioses are Select one: a. relationships where one species lives inside the other's body. b. any relationship with two unrelated species. c. all negative relationships. d. all positive relationships.

b. any relationship with two unrelated species. CorrectFEEDBACK: Symbioses occur when two unrelated species associate. Mutualisms and parasitisms are both considered symbioses. Endosymbioses are a subset of these relationships as well.

Emerging clades include all of the following EXCEPT Select one: a. environmental samples. b. laboratory strains. c. candidate species. d. uncultured organisms.

b. laboratory strains. CorrectFEEDBACK: Emerging clades are those species that are undescribed as yet, which may be due to not being able to culture them so only having DNA data, having just collected them from the environment and only having DNA data, or the species has been described beyond DNA but has not been recognized as a species fully, so is a candidate species.

Reductive evolution is the Select one: a. evolutionary decrease in body size of organisms over time. b. loss or mutation of DNA encoding unselected traits. c. opposite of oxidative evolution. d. decrease in species number over time due to extinction.

b. loss or mutation of DNA encoding unselected traits. Correct FEEDBACK: Reductive evolution is the loss or mutation of DNA that encodes unselected traits. If a trait is not selected for, mutations can accumulate. There is no such thing as oxidative evolution.

Which of the following is true of rRNA sequences? Select one: a. They resist being amplified by PCR. b. The genes encoding them are only present in some organisms. c. Certain regions of rRNAs are highly conserved among organisms. d. They cannot be used to construct phylogenetic trees.

c. Certain regions of rRNAs are highly conserved among organisms. Correct FEEDBACK: Since certain regions of rRNA are highly conserved among organisms, PCR primers can be designed against these regions to amplify rRNAs from different organisms. The sequences in between the primers will differ, allowing rRNA sequences to be used to construct phylogenetic trees.

Which of the following have NOT been used as evidence for life during the Archaean eon? Select one: a. Fossil stromatolites b. Chemical biosignatures c. Fossil eukaryotes d. Isotope ratios

c. Fossil eukaryotes Correct FEEDBACK: Early eukaryotes appeared in the Mesoproterozoic era, many millions of years after the end of the Archaean eon.

Which of the following is correct regarding stromatolites? Select one: a. Fossil stromatolites are made of layers of igneous rock. b. Living stromatolites grow on the deepest parts of the ocean floor as mats of cyanobacteria. c. Stromatolites are the oldest forms of life for which there is clear fossil evidence. d. Living stromatolites can be found in the human colon.

c. Stromatolites are the oldest forms of life for which there is clear fossil evidence. Correct FEEDBACK: Microbial mats of present-day stromatolites resemble the overall wavy structure of fossil ones. Different types of bacteria associate to form stromatolites using different types of light as their source of energy.

Mitochondria and chloroplasts are surrounded by Select one: a. a single membrane. b. a double membrane, the inner one from the host and the outer one from the bacterial endosymbiont. c. a double membrane, the inner one from the bacterial endosymbiont and the outer one derived from the host. d. three membranes.

c. a double membrane, the inner one from the bacterial endosymbiont and the outer one derived from the host. Correct FEEDBACK: Mitochondria and chloroplasts are surrounded by a double membrane. The inner membrane is from the bacterial endosymbiont. In organisms where chloroplasts originated from secondary symbiosis, the organelles have more than two membranes.

Cyanobacteria changed the atmosphere on early Earth because they led to increased Select one: a. nitrogen levels. b. reduced, soluble forms of iron. c. atmospheric O2 levels. d. water levels in the oceans.

c. atmospheric O2 levels. Correct FEEDBACK: Cyanobacteria are capable of oxygenic photosynthesis, using light to split water with the production of oxygen gas as a byproduct.

Although the exact definition of a species for prokaryotes is debated, two individual bacteria can often be considered members of a single species if they Select one: a. can mate and produce fertile offspring. b. have a high degree of morphological similarity. c. have a high degree of DNA similarity. d. can be cocultured because they have the same growth requirements.

c. have a high degree of DNA similarity. Correct FEEDBACK: DNA similarity can be used to assign organisms to a given species. Many different species can have the same growth requirements or morphologies. Bacteria do not undergo sexual reproduction.

What assumption is made when a molecular clock is used to date species divergence? Select one: a. In cells, the rate of protein turnover is 24 hours. b. All cells have a one-day doubling time. c. All species contain the same genes. d. The mutation rate remains constant.

d. The mutation rate remains constant. Correct FEEDBACK: The molecular clock assumes that mutation rates remain constant. The same gene should be compared between species, but not all genes need to be conserved among the species being compared. Cells being compared should have similar doubling times, but the time does not have to be one day. Protein turnover rate in an extant cell is irrelevant to the use of the protein as a molecular clock.

The core genome is Select one: a. the whole chromosomal genome but without plasmids. b. all expected genes in all possible isolates. c. the whole chromosomal genome and all plasmid genes. d. all genes found in all sequenced genomes of a species.

d. all genes found in all sequenced genomes of a species. CorrectFEEDBACK: The core genome is all genes from all sequenced genomes. However, not all isolates are sequenced, and many strains have different genes. The pan-genome is a theoretical total of all genes in these isolates.

The taxonomic rank "order" belongs between Select one: a. domain and phylum. b. family and genus. c. genus and species. d. class and family.

d. class and family. Correct FEEDBACK: The rankings are domain, phylum, class, order, family, genus, species.

A major mechanism of microbial evolution is genome duplication and divergence as discussed in Chapter 9. This allows for existing genes to acquire mutations as there is a "backup" copy of the gene that will continue to function. Genes that have diverged through mutation to have different function are called Select one: a. analogs. b. orthologs. c. homologs. d. paralogs.

d. paralogs. CorrectFEEDBACK: Paralogs are identified through sequence alignment to show both their similarity and subsequent divergence.