Question 1

Clostridium and Escherichia coli are both well-known genera of rod-shaped bacteria, but they are classified into different groups based on their peptidoglycan content.If Clostridium stains purple during a Gram stain test, then we know that E.coli is
A) an archaeon.
B) Gram-positive.
C) a eukaryote.
D) Gram-negative.
E) a spirochete.

Accepted Answer

If Clostridium stains purple during a Gram stain test, it means that it is Gram-positive. Therefore, E.coli, which is classified into a different group based on its peptidoglycan content, is likely Gram-negative.

Question 2

Refer to the figure, which shows a scatterplot of genome size versus number of protein-coding genes found in different classes of microbes.  Based on these data, state and justify the most likely origin of the mimivirus, and present an alternative hypothesis for the origin of this and other viruses.

Accepted Answer

The answer of Refer to the figure, which shows a...

Question 3

Which of the following is a property of eukaryotes but not of prokaryotes?
A) Possession of cell membranes
B) Semiconservative DNA replication
C) A single circular chromosome and plasmids
D) Distinctive photosynthetic membrane systems
E) Membrane-enclosed cytoplasmic organelles

Accepted Answer

Eukaryotes are characterized by the presence of membrane-enclosed organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus, which are absent in prokaryotes. Prokaryotes do not have any membrane-enclosed organelles and their DNA is circular and lacks histones. They also lack the complex cytoskeleton found in eukaryotic cells.

Question 4

As a U.S.Department of Agriculture field representative, you counsel a young farmer to plant alfalfa in fields with soils that have low nitrogen levels.You know alfalfa roots are hosts for nitrogen-fixing bacteria.How will the alfalfa and its associated bacteria help "fertilize" this farmer's soil?

Accepted Answer

The answer of As a U.S.Department of Agriculture field representative,...

Question 5

Which statement regarding the forces that shaped the evolution of Bacteria and Archaea is false?
A) Mutations are an important source of variation. 
B) Lateral gene transfer has played a role in the evolution of the prokaryotic groups.
C) Prokaryotes can acquire new alleles through the process of conjugation.
D) Mutations in prokaryotes have an immediate impact on the cell.
E) Lateral gene transfer in prokaryotes occurs only through the process of transduction.

Accepted Answer

Lateral gene transfer in prokaryotes does not occur only through the process of transduction, but also through conjugation and transformation. Therefore, statement E is false.

Question 6

Recessive mutations in prokaryotes exert their effects immediately because prokaryotes are effectively _______.Mutations can move quickly through populations of prokaryotes by _______ and _______ of the mutated cell.
A) haploid; lateral gene transfer; binary fission
B) diploid; transformation; mitosis
C) haploid; transduction; binary fission
D) diploid; conjugation; meiosis
E) haploid; lateral gene transfer; mitosis

Accepted Answer

Prokaryotes are haploid, meaning they only have one copy of each chromosome. Recessive mutations in prokaryotes are immediately expressed because there is no functional copy of the gene to mask the effects of the mutated gene. Additionally, prokaryotes can transfer genetic material laterally through processes such as conjugation, transformation, and transduction. Binary fission, not mitosis, is the process by which prokaryotes reproduce, further allowing mutations to quickly spread through populations.

Question 7

Refer to the figure.  Based on the figure, which statement is true?
A) Bacteria and Eukarya are both monophyletic groups.
B) Eukarya and Archaea together form a paraphyletic group.
C) Eukarya and Bacteria together form a monophyletic group.
D) Bacteria, Eukarya, and Archaea together form a paraphyletic group.
E) A group consisting of Bacteria and Eukarya is monophyletic.

Accepted Answer

The figure shows two main monophyletic groups, one containing Bacteria and the other containing Eukarya. Therefore, statement A is true.

Question 8

Refer to the figure.  The phylogenetic tree shows that
A) bacteria lost the mitochondrion and the chloroplast.
B) the eukaryotic mitochondrion was acquired through endosymbiosis from bacteria.
C) bacteria obtained the chloroplast endosymbiotically.
D) the eukaryotic mitochondrion and chloroplast were obtained simultaneously in a single event.
E) the mitochondrion evolved independently three times.

Accepted Answer

The phylogenetic tree shows that eukaryotes and bacteria are separate, but share a common ancestor. Within the eukaryotic lineage, there are two separate branches, one containing organisms with mitochondria and the other containing organisms with chloroplasts. This suggests that the acquisition of mitochondria and chloroplasts occurred independently through endosymbiosis from bacteria. Option A is incorrect because bacteria did not lose the mitochondrion and chloroplast as they do not possess them. Option C is incorrect because there is no evidence of bacterial chloroplast endosymbiosis. Option D is incorrect because the acquisition of mitochondria and chloroplasts occurred independently. Option E is incorrect because the phylogenetic tree shows only two separate branches, one for organisms with mitochondria and one for organisms with chloroplasts.

Question 9

Which of the following characteristics is not shared by Archaea, Bacteria, and Eukarya?
A) Semiconservative replication of DNA
B) DNA organized within a membrane-bound nucleus
C) Ribosomes
D) Protein-synthesizing systems
E) Glycolysis

Accepted Answer

Archaea and Bacteria do not have a membrane-bound nucleus, while Eukarya does.

Question 10

Observable phenotypic characteristics, such as a reaction to the Gram stain, are less useful than molecular traits for understanding the evolutionary relationships of prokaryotes.Which statement about the importance of rRNA to the classification of organisms is false?
A) Because rRNA is ancient, it is useful for evolutionary studies.
B) All free-living organisms have rRNA, making it useful for evolutionary studies.
C) Because it plays the same role in translation in all organisms, rRNA is useful for evolutionary studies.
D) Unique sequences in rRNA are useful for distinguishing relationships at the domain level, but not at lower taxonomic levels.
E) Because rRNA has evolved slowly and sequence similarities between groups of organisms are easily found, it is useful for evolutionary studies.

Accepted Answer

Unique sequences in rRNA are indeed useful for distinguishing relationships at various taxonomic levels, not just at the domain level. This makes statement D false. rRNA sequences can provide valuable information for phylogenetic studies across a wide range of taxonomic categories, from broad classifications down to species-level distinctions.

Question 11

Which of the following is a property of prokaryotes but not of eukaryotes?
A) A single circular chromosome and plasmids
B) Possession of cell membranes
C) DNA as the genetic material used to code for proteins
D) Possession of ribosomes
E) Membrane-enclosed cytoplasmic organelles

Accepted Answer

Prokaryotes have a single circular chromosome and plasmids, while eukaryotes have multiple linear chromosomes.

Question 12

Peptidoglycan is a unique feature of the
A) Eukarya.
B) group formed of Bacteria and Eukarya.
C) Bacteria.
D) prokaryotes.
E) Archaea.

Accepted Answer

Peptidoglycan is a major component of the cell wall of bacteria, and is not found in archaea or eukarya.

Question 13

After completing a course of antibiotics that target peptidoglycan, a patient is still suffering from diarrhea.Which would not be a reasonable explanation?
A) The diarrhea is being caused by a eukaryotic microorganism.
B) The bacterium has formed a biofilm, shielding it from antibiotics.
C) The bacterium responsible is from the mycoplasma group of bacteria.
D) The bacterium has acquired antibiotic resistance through lateral gene transfer.
E) The patient is infected with several different Gram-positive bacteria that are not susceptible to this antibiotic.

Accepted Answer

The statement in option E is not a reasonable explanation because antibiotics targeting peptidoglycan are generally effective against Gram-positive bacteria, which have a thick peptidoglycan layer. If the patient is infected with Gram-positive bacteria, they should be susceptible to the antibiotic unless they have specific resistance mechanisms.

Question 14

Why aren't viruses placed on the tree of life for classification, as most other organisms are?

Accepted Answer

The answer of Why aren't viruses placed on the tree...

Question 15

Comparisons of entire genomes among prokaryotes have revealed a stable core of crucial genes that are unaffected by lateral gene transfer.Which statement concerning this discovery is false?
A) Genes involved in fundamental cellular processes are unlikely to be replaced by lateral gene transfer.
B) Lateral gene transfer enables rapid acquisition of traits adapted to specific environments.
C) The discovery will facilitate understanding of phylogenetic relationships of prokaryotes.
D) The results must be treated cautiously because of the small percentage of prokaryotes for which entire genomes are known.
E) Lateral gene transfer makes reconstructing evolutionary patterns among prokaryotes almost impossible.

Accepted Answer

This statement is false. Although lateral gene transfer can make reconstructing evolutionary patterns among prokaryotes more challenging, it is not impossible. The stable core of crucial genes provides a framework for understanding the relationships among prokaryotes, and phylogenetic analysis can still be used to construct evolutionary trees.

Question 16

Differentiate between the following terms:
obligate anaerobe / obligate aerobe
photoautotroph / photoheterotroph
chemoautotroph / chemoheterotroph

Accepted Answer

The answer of Differentiate between the following terms:
obligate anaerobe /...

Question 17

The phylogeny of prokaryotes
A) reveals that spirochetes are the most ancient existing bacterial species.
B) is completely resolved.
C) is easily understood, because of the phenomenon of lateral gene transfer.
D) is now based on gene sequences.
E) reveals that the Archaea and Bacteria do not share a common ancestor.

Accepted Answer

The phylogeny of prokaryotes is now based on gene sequences, which allows for more accurate classification and understanding of evolutionary relationships among different prokaryotic groups.

Answer: A
 The idea that spirochetes are the most ancient existing bacterial species is a hypothesis, but it is not universally accepted and there is not enough evidence to confirm it.

Answer: E
 The Archaea and Bacteria are thought to have diverged from a common ancestor, and share many features such as the absence of a nucleus and the presence of circular chromosomes. Therefore, they are believed to be part of the same domain of life.

Answer: C
 Lateral gene transfer (the transfer of genetic material between different organisms) can make the interpretation of prokaryotic phylogenies more complicated, but it does not prevent their understanding.

Question 18

Refer to the figure.  Judging only from the morphology of the cells, which bacterial genus could this micrograph be showing?
A) Enterococcus
B) Staphylococcus
C) Bacillus
D) Leptospira
E) Actinomyces

Accepted Answer

The cells in the micrograph show the typical morphology of Bacillus, which are rod-shaped with a characteristic "bamboo-like" appearance. Enterococcus and Staphylococcus are cocci-shaped and do not match the morphology seen in the image. Leptospira are spiral-shaped bacteria and Actinomyces are branching, filamentous bacteria, neither of which match the morphology seen in the image.

Question 19

Biologists have hypothesized that high temperatures characterized the early conditions of life on Earth.Which statement would provide the best support for this hypothesis?
A) Human intestinal microbial biota function best at temperatures near the boiling point of water.
B) Bacteria that normally live on human skin thrive at temperatures around 55°C.
C) Most eukaryotic species flourish at temperatures found in hot springs.
D) Reconstructions of ancestral bacterial genes show that the ancestral sequences functioned best at elevated temperatures.
E) The monophyly of the hyperthermophilic bacteria is well established.

Accepted Answer

The reconstruction of ancestral bacterial genes and the finding that they functioned best at elevated temperatures provides direct evidence that high temperatures may have characterized the early conditions of life on Earth. The other choices either do not provide evidence for high temperatures in early Earth conditions or are not directly related to the hypothesis.

Question 20

Thermotoga maritima is a bacterium that can survive extremely high temperatures.Some of its genes most resemble those of archaea that live in similar extreme environments.This is most likely the result of
A) endosymbiosis.
B) lateral gene transfer.
C) conjugation.
D) convergent evolution.
E) common ancestry.

Accepted Answer

The presence of genes in Thermotoga maritima that resemble those found in archaea suggests lateral gene transfer, where genetic material is transferred between distantly related organisms, rather than the other options listed. Endosymbiosis involves one organism living inside another, which is not the case here. Conjugation is a process by which bacteria can transfer DNA to one another but does not explain the similarities between Thermotoga maritima and archaea. Convergent evolution occurs when similar traits evolve independently in different organisms and would not necessarily result in shared genetic material. Finally, while common ancestry can explain similarities between organisms, the specific scenario described here suggests lateral gene transfer is more likely.

Quiz 25: Bacteria, Archaea, and Viruses

Clostridium and Escherichia coli are both well-known genera of rod-shaped bacteria, but they are classified into different groups based on their peptidoglycan content.If Clostridium stains purple during a Gram stain test, then we know that E.coli is

Refer to the figure, which shows a scatterplot of genome size versus number of protein-coding genes found in different classes of microbes. Based on these data, state and justify the most likely origin of the mimivirus, and present an alternative hypothesis for the origin of this and other viruses.

Which of the following is a property of eukaryotes but not of prokaryotes?

As a U.S.Department of Agriculture field representative, you counsel a young farmer to plant alfalfa in fields with soils that have low nitrogen levels.You know alfalfa roots are hosts for nitrogen-fixing bacteria.How will the alfalfa and its associated bacteria help "fertilize" this farmer's soil?

Which statement regarding the forces that shaped the evolution of Bacteria and Archaea is false?

Recessive mutations in prokaryotes exert their effects immediately because prokaryotes are effectively ___.Mutations can move quickly through populations of prokaryotes by _ and _____ of the mutated cell.

Refer to the figure. Based on the figure, which statement is true?

Refer to the figure. The phylogenetic tree shows that

Which of the following characteristics is not shared by Archaea, Bacteria, and Eukarya?

Observable phenotypic characteristics, such as a reaction to the Gram stain, are less useful than molecular traits for understanding the evolutionary relationships of prokaryotes.Which statement about the importance of rRNA to the classification of organisms is false?

Which of the following is a property of prokaryotes but not of eukaryotes?

Peptidoglycan is a unique feature of the

After completing a course of antibiotics that target peptidoglycan, a patient is still suffering from diarrhea.Which would not be a reasonable explanation?

Why aren't viruses placed on the tree of life for classification, as most other organisms are?

Comparisons of entire genomes among prokaryotes have revealed a stable core of crucial genes that are unaffected by lateral gene transfer.Which statement concerning this discovery is false?

Differentiate between the following terms: obligate anaerobe / obligate aerobe photoautotroph / photoheterotroph chemoautotroph / chemoheterotroph

The phylogeny of prokaryotes

Refer to the figure. Judging only from the morphology of the cells, which bacterial genus could this micrograph be showing?

Biologists have hypothesized that high temperatures characterized the early conditions of life on Earth.Which statement would provide the best support for this hypothesis?

Thermotoga maritima is a bacterium that can survive extremely high temperatures.Some of its genes most resemble those of archaea that live in similar extreme environments.This is most likely the result of