Question 1

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

If the experimental population of E. coli lacks an F factor or F plasmid, and if bacteriophages are excluded from the bacterial cultures, then beneficial mutations might be transmitted horizontally to other E. coli cells via ________.

Accepted Answer

If the population of E. coli lacks an F factor or F plasmid, and bacteriophages are excluded from the bacterial cultures, then beneficial mutations might be transmitted horizontally to other E. coli cells via transformation, which is the process by which DNA is released into the environment, taken up by a recipient cell, and integrated into the recipient cell's genome. Sex pili are involved in conjugation, and transduction involves the transfer of DNA mediated by bacteriophages. However, in this experiment, bacteriophages are excluded, so transduction is not a possible mechanism of transfer.

Question 2

In a hypothetical situation, the genes for sex pilus construction and for tetracycline resistance are located on the same plasmid within a particular bacterium. If this bacterium readily performs conjugation involving a copy of this plasmid, then the result should be the ________.

Accepted Answer

When this bacterium undergoes conjugation and transfers the plasmid containing genes for sex pilus construction and tetracycline resistance, it can potentially spread tetracycline resistance to other bacteria in that habitat. This is due to the horizontal transfer of the plasmid between bacteria, allowing for the rapid spread of antibiotic resistance genes.

Question 3

Use the following information to answer the question.
Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free oxygen (O₂) reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocysts are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates."
Given that the enzymes that catalyze nitrogen fixation are inhibited by oxygen, what mechanism might nitrogen-fixing prokaryotes use to protect these enzymes from oxygen?

Accepted Answer

Nitrogen-fixing prokaryotes might live in anaerobic environments or have specialized structures like heterocysts to protect nitrogenase from oxygen, as oxygen inhibits the enzyme.

Question 4

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

E. coli cells typically make most of their ATP by metabolizing glucose. Under the conditions of this experiment, E. coli generation times in the experimental lines and low-glucose conditions should ________.

Accepted Answer

E. coli cells typically make most of their ATP by metabolizing glucose. With low-glucose conditions, the cells would have reduced energy supply, leading to slower generation times.

Question 5

Use the following information and figure to answer the question.
The sea slug Pteraeolidia ianthina (P. ianthina) can harbor living dinoflagellates (photosynthetic protists) in its skin. These endosymbiotic dinoflagellates reproduce quickly enough to maintain their populations. Low populations of the dinoflagellates do not affect the sea slugs very much, but high populations (> 5 x 10⁵ cells/mg of sea slug protein) can promote sea slug survival.

Percent of sea slug respiratory carbon demand provided by indwelling dinoflagellates.
Which of the following would be a potential disadvantage to the sea slugs of housing the dinoflagellates?

Accepted Answer

The answer of Use the following information and figure to...

Question 6

Use the following information and figure to answer the question.
The sea slug Pteraeolidia ianthina (P. ianthina) can harbor living dinoflagellates (photosynthetic protists) in its skin. These endosymbiotic dinoflagellates reproduce quickly enough to maintain their populations. Low populations of the dinoflagellates do not affect the sea slugs very much, but high populations (> 5 x 10⁵ cells/mg of sea slug protein) can promote sea slug survival.

Percent of sea slug respiratory carbon demand provided by indwelling dinoflagellates.
If we assume that carbon is the sole nutrient needed by sea slugs to drive their cellular respiration, then based on the graph, during which season(s) is it least necessary for P. ianthina to act as a chemoheterotroph?

Accepted Answer

During the summer, the percent of respiratory carbon demand provided by indwelling dinoflagellates is the highest, indicating that sea slugs are relying less on chemoheterotrophy during this season. Therefore, it is least necessary for P. ianthina to act as a chemoheterotroph during the summer.

Question 7

Which of the following is least associated with the others?

Accepted Answer

Horizontal gene transfer, conjugation, and transformation are all methods of genetic exchange between organisms. Binary fission is a method of asexual reproduction in which a single parent cell divides into two identical daughter cells. It is not related to genetic exchange.

Question 8

Use the following information and graph to answer the question.
The figure below depicts changes to the amount of DNA present in a recipient cell that is engaged in conjugation with an Hfr cell. Hfr cell DNA begins entering the recipient cell at Time A. Assume that reciprocal crossing over occurs (in other words, a fragment of the recipient's chromosome is exchanged for a homologous fragment from the Hfr cell's DNA).

During which two times can the recipient accurately be described as "recombinant" due to the sequence of events portrayed in the figure?

Accepted Answer

The answer of Use the following information and graph to...

Question 9

Use of synthetic fertilizers often leads to the contamination of groundwater with nitrates. Nitrate pollution is also a suspected cause of anoxic "dead zones" in the ocean. Which of the following might help reduce nitrate pollution?

Accepted Answer

Growing improved crop plants that have nitrogen-fixing enzymes can reduce the need for synthetic fertilizers, resulting in less nitrate pollution. Nitrogen-fixing enzymes allow plants to obtain nitrogen from the atmosphere, which can be used to synthesize organic molecules. This reduces the need for nitrogen fertilizers and reduces nitrate pollution. Options B and C add bacteria to the soil, but it is not guaranteed that they will reduce nitrate pollution. Option D is not a suitable solution as ammonia can also lead to nitrate pollution.

Question 10

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

If the vertical axis of the figure above refers to relative fitness, then which of the following is the most valid and accurate measure of fitness?

Accepted Answer

The answer of The following question refers to the figure.
In...

Question 11

Biologists sometimes divide living organisms into two groups: autotrophs and heterotrophs. These two groups differ in ________.

Accepted Answer

Autotrophs make their own organic molecules (carbon-containing molecules) from inorganic sources, while heterotrophs rely on consuming organic molecules made by other organisms. The other choices (B, C, and D) are not accurate distinctions between autotrophs and heterotrophs.

Question 12

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

Compare the bacteria in the figure above in generation 1 and generation 20,000. The bacteria in generation 1 have a greater ________.

Accepted Answer

The bacteria in generation 1 have a greater reliance on glycolytic enzymes because they are not as efficient at using low-glucose conditions as the bacteria in generation 20,000. Over the course of 20,000 generations, the bacteria evolved to be more efficient at using the limited glucose available in their environment, which led to a decreased reliance on glycolytic enzymes.

Question 13

The following table depicts characteristics of five prokaryotic species (A-E). Use the information in the table to answer the question.

Which species might include cells that are Hfr cells?

Accepted Answer

The answer of The following table depicts characteristics of five...

Question 14

Use the following information to answer the question.
Nitrogenase, the enzyme that catalyzes nitrogen fixation, is inhibited whenever free oxygen (O₂) reaches a critical concentration. Consequently, nitrogen fixation cannot occur in cells wherein photosynthesis produces free O₂. Consider the colonial aquatic cyanobacterium, Anabaena, whose heterocysts are described as having "...a thickened cell wall that restricts entry of O₂ produced by neighboring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighboring cells in exchange for carbohydrates."
Think about this description of the colonial aquatic cyanobacterium, Anabaena. Which of the following questions below is important for understanding how nitrogen (N₂) enters heterocysts, and how oxygen (O₂) is kept out of heterocysts?

Accepted Answer

The question addresses the mechanism by which heterocysts selectively allow the entry of certain molecules like carbohydrates while preventing the entry of oxygen, which is crucial for understanding how nitrogen fixation is protected from oxygen interference.

Question 15

A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. The cell also lacks F factors and F plasmids. Which of the following statements about the bacteria is most probably accurate?

Accepted Answer

The fact that the bacterium lacks F factors and F plasmids means it cannot donate DNA through conjugation with another cell.

Question 16

A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan. This bacterium derives nutrition by digesting human intestinal contents. Thus, this bacterium is an ________.

Accepted Answer

The bacterium derives nutrition by digesting human intestinal contents, indicating that it is a heterotroph. It also does not require oxygen for respiration, as it is found in the intestinal tract, which can be anaerobic. Therefore, the bacterium is an anaerobic chemoheterotroph. The fact that it is not susceptible to the penicillin family of antibiotics and contains no plasmids are additional characteristics that support this classification.

Question 17

The following table depicts characteristics of five prokaryotic species (A-E). Use the information in the table to answer the question.

Which two species might be expected to cooperate metabolically, perhaps forming a biofilm wherein one species surrounds cells of the other species?

Accepted Answer

The answer of The following table depicts characteristics of five...

Question 18

The following question refers to the figure.
In this eight-year experiment, 12 populations of E. coli, each begun from a single cell, were grown in low-glucose conditions for 20,000 generations. Each culture was introduced to fresh growth medium every 24 hours. Occasionally, samples were removed from the populations, and their fitness in low-glucose conditions was tested against that of members sampled from the ancestral (common ancestor) E. coli population.

Which term best describes what has occurred among the experimental populations of cells over this eight-year period?

Accepted Answer

The experiment describes changes in the fitness of populations over time, which is an example of microevolution. There is no evidence of speciation, adaptive radiation, or stabilizing selection based on the information given.

Question 19

The following table depicts characteristics of five prokaryotic species (A-E). Use the information in the table to answer the question.

Species D is pathogenic if it gains access to the human intestine. Which other species, if it coinhabited a human intestine along with species D, is most likely to become a recombinant species that is both pathogenic and resistant to some antibiotics?

Accepted Answer

The answer of The following table depicts characteristics of five...

Question 20

Data were collected from the heterocysts of a nitrogen-fixing cyanobacterium inhabiting equatorial ponds. Study the graph and choose the most likely explanation for the shape of the curve.

Accepted Answer

The shape of the curve suggests that nitrogen fixation is inhibited during peak photosynthesis, likely due to the influx of oxygen into the heterocysts.

Quiz 27: Bacteria and Archaea

In a hypothetical situation, the genes for sex pilus construction and for tetracycline resistance are located on the same plasmid within a particular bacterium. If this bacterium readily performs conjugation involving a copy of this plasmid, then the result should be the ________.

Which of the following is least associated with the others?

Use of synthetic fertilizers often leads to the contamination of groundwater with nitrates. Nitrate pollution is also a suspected cause of anoxic "dead zones" in the ocean. Which of the following might help reduce nitrate pollution?

Biologists sometimes divide living organisms into two groups: autotrophs and heterotrophs. These two groups differ in ________.

The following table depicts characteristics of five prokaryotic species (A-E) . Use the information in the table to answer the question. Which species might include cells that are Hfr cells?

The following table depicts characteristics of five prokaryotic species (A-E) . Use the information in the table to answer the question. Which two species might be expected to cooperate metabolically, perhaps forming a biofilm wherein one species surrounds cells of the other species?

Data were collected from the heterocysts of a nitrogen-fixing cyanobacterium inhabiting equatorial ponds. Study the graph and choose the most likely explanation for the shape of the curve.