Question 1

Use the following information and figure to answer the question.
The sea slug Pteraeolidia ianthina (P. ianthina) can harbour 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.
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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 summer, the graph likely shows higher levels of carbon availability, reducing the need for P. ianthina to rely on chemoheterotrophy for energy.

Question 2

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 metabolising glucose. Under the conditions of this experiment, E. coli generation times in the experimental lines and low-glucose conditions should ________.

Accepted Answer

Under low-glucose conditions, E. coli cells will have slower generation times compared to typical conditions, as glucose is the primary source of energy for the cells and its scarcity will slow down metabolic processes.

Question 3

Use the following information and figure to answer the question.
The sea slug Pteraeolidia ianthina (P. ianthina) can harbour 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 sea slugs are exposed to predators when they spend time in the sunlit areas needed by the dinoflagellates.

Question 4

Which of the following is least associated with the others?

Accepted Answer

Binary fission is the process by which prokaryotic cells divide into two identical daughter cells, while horizontal gene transfer (including conjugation and transformation) involves the transfer of genetic material between different cells.

Question 5

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

Accepted Answer

The experiment shows the evolutionary changes that have occurred within the populations of E. coli over time due to environmental pressure (low-glucose conditions). These changes are considered microevolution because they involve changes in the gene pool of a single species over a relatively short period of time (8 years). There is no evidence of speciation or adaptive radiation in this experiment, and while stabilizing selection may contribute to the observed changes, it does not fully describe the process of evolution that has occurred.

Question 6

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

Accepted Answer

Autotrophs are organisms that can synthesize their own organic molecules from inorganic sources, such as carbon dioxide. Heterotrophs, on the other hand, must obtain organic molecules from other organisms as a source of carbon. This is the primary difference between the two groups.

Question 7

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. Faecal 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 bacterium lacks F factors and F plasmids, which are necessary for conjugation.

Question 8

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 experimental population of E. coli lacks an F factor or F plasmid, it cannot participate in conjugation, and bacteriophages are excluded from the bacterial cultures, so horizontal gene transfer can only occur via transformation. This process involves the uptake and incorporation of DNA from the environment into the bacterial genome. Sex pili are structures involved in conjugation, and transduction involves the transfer of genetic material via bacteriophages.

Question 9

Nitrogenase, the enzyme that catalyses 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 neighbouring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighbouring cells in exchange for carbohydrates".
Given that the enzymes that catalyse nitrogen fixation are inhibited by oxygen, what mechanism might nitrogen-fixing prokaryotes use to protect these enzymes from oxygen?

Accepted Answer

Nitrogen-fixing prokaryotes may live in anaerobic environments or use specialized structures like heterocysts to protect nitrogenase from oxygen.

Question 10

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 11

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. Faecal 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 in the scenario obtains its nutrition by digesting human intestinal contents, indicating that it is a heterotroph. Additionally, it is described as lacking plasmids and containing relatively little peptidoglycan, which are characteristics commonly found in gram-negative bacteria. The bacterium is also resistant to penicillin, which further supports the idea that it is a gram-negative bacterium with an outer membrane that prevents the antibiotic from reaching its target. This bacterium is also able to withstand boiling, which indicates the presence of spores, but no information has been provided about the oxygen requirements of the bacterium. Therefore, the best choice for this bacterium is option C - anaerobic chemoheterotroph.

Question 12

Use of synthetic fertilisers 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 would reduce the need for synthetic fertilisers, leading to a decrease in nitrate pollution. Option B would only convert ammonia to nitrate, therefore exacerbating the problem. Option C would convert nitrate to gaseous nitrogen, which would reduce the amount of nitrogen available for the plant to utilise. Therefore, option A is the best choice to reduce nitrate pollution. Option D would still involve the use of synthetic fertilisers and would not address the issue of nitrate pollution.

Question 13

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

Since the plasmid contains both the genes for sex pilus construction and for tetracycline resistance, conjugation would result in transfer of both traits to the recipient bacterium. Therefore, the rapid spread of tetracycline resistance to other bacteria in that habitat would occur.

Question 14

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

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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

Species C is most likely to become a recombinant species that is both pathogenic and resistant to some antibiotics because it is the only species that is both pathogenic and resistant to antibiotics.

Question 15

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

Accepted Answer

Recombination typically occurs during times when genetic material is exchanged or rearranged. In the context of the figure, times C and D likely represent phases where such genetic recombination events occur, such as during meiosis or bacterial conjugation.

Question 16

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

During hours of peak photosynthesis, oxygen enters the heterocysts, which inhibits nitrogen fixation. This means that nitrogen fixation is lower during those hours, resulting in the lower point on the curve. As oxygen levels decrease, nitrogen fixation increases, resulting in the peak of nitrogen fixation during hours of lower photosynthesis.

Question 17

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

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Which species might include cells that are Hfr cells?

Accepted Answer

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

Question 18

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 In this eight-year experiment, 12 populations of...

Question 19

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. 
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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 figure shows that the bacteria in generation 1 have a higher growth rate but a lower fitness compared to the bacteria in generation 20,000. This indicates that the bacteria in generation 1 are relying more on glycolytic enzymes to metabolize glucose, which allows them to grow faster but also makes them less fit in low-glucose conditions. In contrast, the bacteria in generation 20,000 have evolved to rely less on glycolytic enzymes and more on other metabolic pathways, which may allow them to better survive in low-glucose conditions. Therefore, choice D is the best answer.

Question 20

Nitrogenase, the enzyme that catalyses 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 neighbouring cells. Intercellular connections allow heterocysts to transport fixed nitrogen to neighbouring 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 prevent oxygen from entering through intercellular connections, which is crucial for understanding how nitrogen fixation is protected from oxygen interference.

Quiz 27: Bacteria and Archaea

Which of the following is least associated with the others?

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

Use of synthetic fertilisers 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?

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 ________.

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.

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?