Microbiology Quiz: Environmental Factors And Growth
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Environmental Factors And GrowthQuestion 1 of 20

A defined minimal medium is prepared with highly purified glucose, ammonium sulfate, potassium phosphate, and water to grow a specific chemoheterotroph. The bacterium exhibits very poor growth. However, when a small amount of yeast extract is added, robust growth occurs. Which of the following is the most likely explanation for this observation?

The yeast extract provides a more easily metabolized carbon source than glucose.
The bacterium is fastidious and requires growth factors that are present in the yeast extract.
The high salt content of the yeast extract is necessary to maintain proper osmotic balance.
The yeast extract acts as a chelating agent, making toxic heavy metals in the water unavailable.
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Microbiology Quiz

Microbiology Quiz: Environmental Factors And Growth

Practice Environmental Factors And Growth in Microbiology with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

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This quiz focuses on Environmental Factors And Growth, giving you a quick way to practice the rules, question types, and explanations that matter most for Microbiology.

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Question 1

A defined minimal medium is prepared with highly purified glucose, ammonium sulfate, potassium phosphate, and water to grow a specific chemoheterotroph. The bacterium exhibits very poor growth. However, when a small amount of yeast extract is added, robust growth occurs. Which of the following is the most likely explanation for this observation?

  1. The yeast extract provides a more easily metabolized carbon source than glucose.
  2. The bacterium is fastidious and requires growth factors that are present in the yeast extract. (correct answer)
  3. The high salt content of the yeast extract is necessary to maintain proper osmotic balance.
  4. The yeast extract acts as a chelating agent, making toxic heavy metals in the water unavailable.
Explanation: Correct: A minimal medium contains only the bare necessities for a prototroph. Yeast extract is a complex additive derived from yeast cells, and it is rich in vitamins, amino acids, purines, and pyrimidines. An organism that cannot synthesize one or more of these essential organic molecules is termed fastidious or auxotrophic. The fact that adding yeast extract permits growth strongly implies the bacterium requires such pre-formed growth factors. A: Glucose is an excellent carbon source for most chemoheterotrophs; this is an unlikely explanation. C: Yeast extract is not primarily a source of salt for osmoregulation. D: While yeast extract may have some chelating properties, its primary role in microbiology is as a rich source of growth factors.

Question 2

A neutrophilic bacterium with an optimal pH of 7.2 is inoculated into two identical culture flasks. Flask A contains a medium buffered at pH 7.2. Flask B contains a medium buffered at pH 5.5. Both are incubated at the optimal temperature. Based on the expected growth curves, which of the following is the most accurate prediction?

  1. The lag phase in Flask B will be longer, and the growth rate during log phase will be slower than in Flask A. (correct answer)
  2. The lag phase in Flask B will be shorter, and the final cell density will be the same as in Flask A.
  3. The growth rate in Flask B will be identical to Flask A, but the stationary phase will be reached sooner.
  4. The culture in Flask B will fail to grow entirely, as the pH is outside its minimum required range.
Explanation: Correct: Growth at a suboptimal pH induces cellular stress. The cells must expend energy to maintain their internal pH homeostasis. This has two major effects on the growth curve: 1) The lag phase is extended as cells adapt their physiology to the stressful condition. 2) The maximum growth rate (slope of the log phase) is reduced because metabolic energy is diverted from growth to maintenance. The final cell density is also typically lower. B: The lag phase will be longer, not shorter, due to the need for adaptation. C: The growth rate will be slower at a suboptimal pH. D: While pH 5.5 is stressful for a neutrophile, it is not typically lethal or completely inhibitory. Most neutrophiles have a growth range of approximately pH 5.5 to 8.5.

Question 3

An unknown bacterium is successfully cultured in a laboratory medium containing peptone (a digest of animal protein), beef extract, and NaCl. It is incubated in the dark at 37°C. Based on this information, the bacterium's nutritional classification is most likely a:

  1. Chemoorganoheterotroph (correct answer)
  2. Chemolithoautotroph
  3. Photoheterotroph
  4. Photoautotroph
Explanation: Correct: The nutritional class can be deduced from the energy and carbon sources. Energy source: The medium contains chemicals (peptone, beef extract), not light (incubated in dark), so it is a 'chemotroph'. Electron source: The electron donors are organic molecules, so it is an 'organotroph'. Carbon source: The organism uses pre-formed organic molecules from the peptone and beef extract, not CO₂, so it is a 'heterotroph'. Combining these gives chemoorganoheterotroph. B: A chemoautotroph would use chemical energy but fix its own carbon from CO₂ and a lithotroph uses inorganic electron donors. C: A photoheterotroph uses light for energy, but the culture was in the dark. D: A photoautotroph uses light for energy and CO₂ for carbon.

Question 4

A microbiologist performs a catalase test on two different bacterial isolates from a wound infection. Isolate A produces vigorous bubbles when a drop of hydrogen peroxide is added. Isolate B produces no bubbles. Both isolates are known to be facultative anaerobes that grow well on an agar plate in air. What is a valid conclusion?

  1. Isolate A is an obligate aerobe, and Isolate B is an obligate anaerobe.
  2. Isolate B is unable to perform aerobic respiration and relies solely on fermentation.
  3. The test on Isolate B was a false negative, as all organisms that tolerate oxygen must produce catalase.
  4. Isolate B must use an alternative enzyme, such as a peroxidase, to neutralize hydrogen peroxide. (correct answer)
Explanation: Correct: The catalase test specifically detects the enzyme catalase. A positive result (bubbles) indicates its presence. A negative result in an organism that can clearly tolerate oxygen (as stated, it's a facultative anaerobe) implies it must use a different enzymatic mechanism to detoxify hydrogen peroxide. The most common alternative is a peroxidase enzyme, which also breaks down H₂O₂ but does not produce O₂ gas (no bubbles). A: This contradicts the premise that both are facultative anaerobes. B: This is incorrect. Many facultative anaerobes, like those in the genus Streptococcus, are catalase-negative but still perform aerobic respiration. C: This is a common but incorrect generalization. Aerotolerant anaerobes and some facultative anaerobes lack catalase and use peroxidases instead.

Question 5

A researcher has a liquid culture of a Salmonella strain that is auxotrophic for tryptophan (trp⁻). The researcher suspects that some cells in the population have undergone a reversion mutation, becoming prototrophic (trp⁺). Which of the following plating strategies would most effectively isolate these rare revertant colonies?

  1. Plate the culture on a complete medium agar containing a high concentration of tryptophan.
  2. Plate the culture on a minimal medium agar supplemented with all 20 amino acids.
  3. Plate the culture on a minimal medium agar lacking any added tryptophan. (correct answer)
  4. Plate the culture on a medium containing an antibiotic to which the original trp⁻ strain is resistant.
Explanation: Correct: This is a selection strategy. A minimal medium provides only the essential salts and a carbon source needed for a prototroph to grow. The trp⁻ auxotrophs cannot synthesize their own tryptophan and will be unable to grow on this medium. Only the rare trp⁺ revertants, which have regained the ability to synthesize tryptophan, will be able to form colonies. This allows for the effective isolation of the revertants from the majority population. A: Both trp⁻ and trp⁺ cells will grow on a complete medium, making it impossible to distinguish them. B: This is another form of complete medium where both cell types would grow. D: This selects for antibiotic resistance, which is an unrelated genetic trait.

Question 6

A clinical isolate is found to be positive for superoxide dismutase (SOD) but negative for catalase. The isolate is inoculated into a tube of fluid thioglycollate medium. Which growth pattern is expected after 24 hours of incubation?

  1. Growth is concentrated at the surface and is absent in the lower portion of the tube.
  2. Growth is concentrated in a narrow band slightly below the surface.
  3. Growth is concentrated at the bottom of the tube and is absent from the surface.
  4. Growth occurs evenly throughout the tube, without a specific concentration at any level. (correct answer)
Explanation: Correct: The presence of superoxide dismutase (SOD) allows the organism to detoxify the O₂⁻ radical, meaning it can survive in the presence of oxygen. The absence of catalase indicates it cannot easily break down hydrogen peroxide (H₂O₂), a byproduct of aerobic respiration. This enzymatic profile is characteristic of an aerotolerant anaerobe, which carries out fermentation and is not harmed by oxygen, thus growing evenly throughout a thioglycollate tube. A: This pattern describes an obligate aerobe, which would be both SOD-positive and catalase-positive. B: This pattern describes a microaerophile, which requires low levels of oxygen and would likely have SOD and potentially low levels of catalase/peroxidase. C: This pattern describes an obligate anaerobe, which would typically lack both SOD and catalase.

Question 7

A facultative anaerobe is being cultured in a liquid medium in a flask open to the atmosphere and incubated on a shaker for aeration. The incubator temperature is increased from 30°C to 45°C, a change that is still within the organism's optimal range for growth. Assuming no other factor is limiting, what is the most likely effect on the organism's metabolism?

  1. A significant increase in the rate of aerobic respiration due to higher enzyme activity.
  2. A shift towards a more fermentative metabolism despite the constant aeration. (correct answer)
  3. A complete cessation of growth due to the accumulation of toxic oxygen species.
  4. A shift to using alternative inorganic electron acceptors like nitrate present in the medium.
Explanation: Correct: This question requires integrating two environmental factors. As temperature increases, the solubility of gases, including oxygen, in the liquid medium decreases. Even though the flask is being aerated, the amount of dissolved oxygen available to the cells will be lower at 45°C than at 30°C. As a facultative anaerobe, the organism will compensate for the reduced oxygen availability by increasing its reliance on anaerobic pathways like fermentation. A: While enzymatic rates increase with temperature, this effect is nullified if the terminal electron acceptor for aerobic respiration (oxygen) becomes more limited. C: Facultative anaerobes possess enzymes to detoxify reactive oxygen species, so this is unlikely. D: While a possibility in some media, the most direct and universal consequence of decreased oxygen solubility is a shift away from aerobic respiration towards fermentation.

Question 8

Two cultures of a mesophilic bacterium are grown to stationary phase in identical media. Culture A is incubated at its optimal temperature of 37°C, while Culture B is incubated at a suboptimal temperature of 25°C. How will the physiology of the cells entering the death phase likely differ between the two cultures?

  1. Cells from Culture B will have a lower endogenous metabolic rate and will remain viable for a longer period. (correct answer)
  2. Cells from Culture A will enter the death phase later due to a more efficient accumulation of storage granules.
  3. Both cultures will have identical rates of viability loss, as cell death is primarily caused by nutrient depletion.
  4. Cells from Culture B will lyse more quickly due to prolonged exposure to suboptimal cold temperatures.
Explanation: Correct: The death phase is characterized by a net loss of viable cells, often due to the depletion of internal energy reserves (endogenous metabolism) and accumulation of toxic byproducts. At a lower temperature (25°C), all metabolic reactions, including these self-destructive ones, proceed more slowly. This lower metabolic rate conserves energy and prolongs the period of viability compared to cells at the optimal temperature (37°C), where reserves are consumed much more quickly. B: Cells at the optimal temperature will deplete resources and reach the death phase faster. C: The rate of viability loss is temperature-dependent. D: 25°C is suboptimal for a mesophile, but it is not a lethal cold shock temperature; it will slow down, not accelerate, cell death.

Question 9

A microbiologist prepares a liquid medium to grow Lactobacillus, a bacterium that produces lactic acid as a primary fermentation product. The initial pH of the medium is 7.0. If the medium is prepared without a buffering agent (e.g., phosphate buffer), what is the most likely consequence for bacterial growth?

  1. The culture will grow to a much higher density than in a buffered medium.
  2. The culture will not grow at all because Lactobacillus requires an acidic environment.
  3. The culture will grow initially, but growth will cease prematurely as end products acidify the medium. (correct answer)
  4. The pH of the medium will gradually increase as the bacteria catabolize proteins.
Explanation: Correct: As Lactobacillus ferments sugars, it produces lactic acid, which is released into the medium. In an unbuffered medium, this acid accumulation will rapidly decrease the pH. Even though Lactobacillus is acid-tolerant, the pH will eventually drop below the minimum required for growth, inhibiting the cell's own enzymes and halting growth long before nutrients are depleted. This phenomenon is known as self-limiting growth. A: The opposite is true; the lack of a buffer will limit the final density. B: While tolerant of acid, Lactobacillus can typically initiate growth at neutral pH. D: The primary metabolism is fermentation of carbohydrates to acid, which will decrease, not increase, the pH.

Question 10

A microbiologist isolates a bacterium from a salt flat that grows optimally in a medium containing 20% NaCl. What is the most likely immediate outcome if this bacterium is transferred to a standard nutrient broth with 0.5% NaCl?

  1. The cell will shrivel (plasmolyze) due to a rapid efflux of water.
  2. The cell will swell and lyse due to a rapid influx of water. (correct answer)
  3. The cell will grow more rapidly due to reduced energetic cost of osmoregulation.
  4. The cell will remain metabolically active but will be unable to divide.
Explanation: Correct: The organism is an extreme halophile. Its cytoplasm has a very high solute concentration to balance the 20% NaCl environment. When transferred to a medium with a much lower solute concentration (0.5% NaCl), the external environment becomes strongly hypotonic relative to the cell's cytoplasm. Water will rush into the cell via osmosis, increasing turgor pressure beyond what the cell wall can withstand, causing it to lyse. A: Plasmolysis (shriveling) occurs when a cell is moved to a hypertonic environment, the opposite of this scenario. C: The enzymes and transport systems of an extreme halophile are adapted to and often require high salt concentrations to maintain their structure and function; they would not function properly in a low-salt medium. D: The osmotic shock is typically too severe and rapid for the cell to simply enter a static state; lysis is the most probable immediate outcome.

Question 11

Many pathogenic bacteria, when invading a human host, face an environment that is rich in most nutrients but extremely limited in free ferric iron (Fe³⁺). Which of the following adaptations is most critical for these bacteria to acquire enough iron to grow and establish an infection?

  1. The ability to switch to metabolic pathways that do not require iron-sulfur cluster enzymes.
  2. Utilizing zinc or manganese as a direct substitute for iron in the heme group of cytochromes.
  3. Synthesizing and secreting high-affinity iron-chelating molecules called siderophores. (correct answer)
  4. Triggering widespread host cell lysis to release intracellular iron stores into the environment.
Explanation: Correct: The human body sequesters iron by binding it to proteins like transferrin, lactoferrin, and ferritin, making it unavailable to invading microbes. The most common bacterial strategy to overcome this is to produce siderophores. These molecules have an extremely high affinity for Fe³⁺, allowing them to strip iron from host proteins. The bacteria then have specific receptors to import the iron-siderophore complex. A: While some metabolic flexibility exists, iron is an essential cofactor for so many critical processes (like respiration) that it cannot be completely bypassed. B: While some metal substitution can occur for certain enzymes, it is not possible to substitute other metals for iron in the heme structure of cytochromes. D: While some pathogens produce toxins that cause cell lysis (hemolysins), siderophore production is a more universal and fundamental strategy for iron acquisition in host tissues.

Question 12

A clinical isolate is found to be positive for superoxide dismutase (SOD) but negative for catalase. The isolate is inoculated into a tube of fluid thioglycollate medium. Which growth pattern is expected after 24 hours of incubation?

  1. Growth is concentrated at the surface and is absent in the lower portion of the tube.
  2. Growth is concentrated in a narrow band slightly below the surface.
  3. Growth is concentrated at the bottom of the tube and is absent from the surface.
  4. Growth occurs evenly throughout the tube, without a specific concentration at any level. (correct answer)
Explanation: Correct: The presence of superoxide dismutase (SOD) allows the organism to detoxify the O₂⁻ radical, meaning it can survive in the presence of oxygen. The absence of catalase indicates it cannot easily break down hydrogen peroxide (H₂O₂), a byproduct of aerobic respiration. This enzymatic profile is characteristic of an aerotolerant anaerobe, which carries out fermentation and is not harmed by oxygen, thus growing evenly throughout a thioglycollate tube. A: This pattern describes an obligate aerobe, which would be both SOD-positive and catalase-positive. B: This pattern describes a microaerophile, which requires low levels of oxygen and would likely have SOD and potentially low levels of catalase/peroxidase. C: This pattern describes an obligate anaerobe, which would typically lack both SOD and catalase.

Question 13

Picrophilus oshimae is an archaeon that grows optimally at an external pH of 0.7. Despite this extreme environment, it maintains its intracellular pH near 7.0. Which of the following mechanisms is most critical for preventing cytoplasmic acidification in this organism?

  1. Possessing enzymes and structural proteins that have an optimal pH near 0.7.
  2. Maintaining a cell membrane with an exceptionally low permeability to protons.
  3. Actively transporting protons out of the cytoplasm using ATP-powered pumps. (correct answer)
  4. Synthesizing a large internal pool of alkaline buffering compounds.
Explanation: Correct: To maintain a pH gradient of over 6 units, the cell must constantly and actively pump protons out of the cytoplasm to counteract the massive influx driven by the concentration gradient. This energetic process is the primary mechanism for maintaining a neutral internal pH. A: This is a common misconception. While some extracellular enzymes may be acid-stable, the intracellular machinery for core processes like DNA replication and translation must operate at a near-neutral pH. B: While having a low-permeability membrane is a helpful adaptation, no membrane is completely impermeable. Passive influx of protons would still overwhelm the cell without an active export mechanism. D: Intracellular buffering can neutralize small amounts of acid but would be quickly exhausted by the continuous influx of protons from a pH 0.7 environment. It is a secondary, not primary, mechanism.

Question 14

A facultative anaerobe is being cultured in a liquid medium in a flask open to the atmosphere and incubated on a shaker for aeration. The incubator temperature is increased from 30°C to 45°C, a change that is still within the organism's optimal range for growth. Assuming no other factor is limiting, what is the most likely effect on the organism's metabolism?

  1. A significant increase in the rate of aerobic respiration due to higher enzyme activity.
  2. A shift towards a more fermentative metabolism despite the constant aeration. (correct answer)
  3. A complete cessation of growth due to the accumulation of toxic oxygen species.
  4. A shift to using alternative inorganic electron acceptors like nitrate present in the medium.
Explanation: Correct: This question requires integrating two environmental factors. As temperature increases, the solubility of gases, including oxygen, in the liquid medium decreases. Even though the flask is being aerated, the amount of dissolved oxygen available to the cells will be lower at 45°C than at 30°C. As a facultative anaerobe, the organism will compensate for the reduced oxygen availability by increasing its reliance on anaerobic pathways like fermentation. A: While enzymatic rates increase with temperature, this effect is nullified if the terminal electron acceptor for aerobic respiration (oxygen) becomes more limited. C: Facultative anaerobes possess enzymes to detoxify reactive oxygen species, so this is unlikely. D: While a possibility in some media, the most direct and universal consequence of decreased oxygen solubility is a shift away from aerobic respiration towards fermentation.

Question 15

A neutrophilic bacterium with an optimal pH of 7.2 is inoculated into two identical culture flasks. Flask A contains a medium buffered at pH 7.2. Flask B contains a medium buffered at pH 5.5. Both are incubated at the optimal temperature. Based on the expected growth curves, which of the following is the most accurate prediction?

  1. The lag phase in Flask B will be longer, and the growth rate during log phase will be slower than in Flask A. (correct answer)
  2. The lag phase in Flask B will be shorter, and the final cell density will be the same as in Flask A.
  3. The growth rate in Flask B will be identical to Flask A, but the stationary phase will be reached sooner.
  4. The culture in Flask B will fail to grow entirely, as the pH is outside its minimum required range.
Explanation: Correct: Growth at a suboptimal pH induces cellular stress. The cells must expend energy to maintain their internal pH homeostasis. This has two major effects on the growth curve: 1) The lag phase is extended as cells adapt their physiology to the stressful condition. 2) The maximum growth rate (slope of the log phase) is reduced because metabolic energy is diverted from growth to maintenance. The final cell density is also typically lower. B: The lag phase will be longer, not shorter, due to the need for adaptation. C: The growth rate will be slower at a suboptimal pH. D: While pH 5.5 is stressful for a neutrophile, it is not typically lethal or completely inhibitory. Most neutrophiles have a growth range of approximately pH 5.5 to 8.5.

Question 16

A container of leftover stew is stored in a refrigerator at 4°C. After several days, spoilage is observed. A bacterium isolated from the stew grows optimally at 25°C but is capable of slow growth at 4°C. This organism is best classified as a:

  1. Psychrophile
  2. Psychrotroph (correct answer)
  3. Mesophile
  4. Thermophile
Explanation: Correct: This question tests the distinction between psychrophiles and psychrotrophs. A psychrophile is a true cold-loving organism with an optimal growth temperature of 15°C or lower. A psychrotroph has a mesophilic optimum (typically 20-30°C) but has adapted to also grow at refrigeration temperatures (0-7°C). Since the isolate's optimum is 25°C but it can grow at 4°C, it is a psychrotroph. These organisms are the primary cause of refrigerated food spoilage. A: A psychrophile would have a much lower optimal temperature. C: While its optimum is in the mesophilic range, 'mesophile' is a general term. 'Psychrotroph' is more specific and accurate because it describes the key characteristic of growth at cold temperatures. D: A thermophile grows at high temperatures.

Question 17

An unknown bacterium is successfully cultured in a laboratory medium containing peptone (a digest of animal protein), beef extract, and NaCl. It is incubated in the dark at 37°C. Based on this information, the bacterium's nutritional classification is most likely a:

  1. Chemoorganoheterotroph (correct answer)
  2. Chemolithoautotroph
  3. Photoheterotroph
  4. Photoautotroph
Explanation: Correct: The nutritional class can be deduced from the energy and carbon sources. Energy source: The medium contains chemicals (peptone, beef extract), not light (incubated in dark), so it is a 'chemotroph'. Electron source: The electron donors are organic molecules, so it is an 'organotroph'. Carbon source: The organism uses pre-formed organic molecules from the peptone and beef extract, not CO₂, so it is a 'heterotroph'. Combining these gives chemoorganoheterotroph. B: A chemoautotroph would use chemical energy but fix its own carbon from CO₂ and a lithotroph uses inorganic electron donors. C: A photoheterotroph uses light for energy, but the culture was in the dark. D: A photoautotroph uses light for energy and CO₂ for carbon.

Question 18

A microbiologist isolates a bacterium from a salt flat that grows optimally in a medium containing 20% NaCl. What is the most likely immediate outcome if this bacterium is transferred to a standard nutrient broth with 0.5% NaCl?

  1. The cell will shrivel (plasmolyze) due to a rapid efflux of water.
  2. The cell will swell and lyse due to a rapid influx of water. (correct answer)
  3. The cell will grow more rapidly due to reduced energetic cost of osmoregulation.
  4. The cell will remain metabolically active but will be unable to divide.
Explanation: Correct: The organism is an extreme halophile. Its cytoplasm has a very high solute concentration to balance the 20% NaCl environment. When transferred to a medium with a much lower solute concentration (0.5% NaCl), the external environment becomes strongly hypotonic relative to the cell's cytoplasm. Water will rush into the cell via osmosis, increasing turgor pressure beyond what the cell wall can withstand, causing it to lyse. A: Plasmolysis (shriveling) occurs when a cell is moved to a hypertonic environment, the opposite of this scenario. C: The enzymes and transport systems of an extreme halophile are adapted to and often require high salt concentrations to maintain their structure and function; they would not function properly in a low-salt medium. D: The osmotic shock is typically too severe and rapid for the cell to simply enter a static state; lysis is the most probable immediate outcome.

Question 19

A microbiologist prepares a liquid medium to grow Lactobacillus, a bacterium that produces lactic acid as a primary fermentation product. The initial pH of the medium is 7.0. If the medium is prepared without a buffering agent (e.g., phosphate buffer), what is the most likely consequence for bacterial growth?

  1. The culture will grow to a much higher density than in a buffered medium.
  2. The culture will not grow at all because Lactobacillus requires an acidic environment.
  3. The culture will grow initially, but growth will cease prematurely as end products acidify the medium. (correct answer)
  4. The pH of the medium will gradually increase as the bacteria catabolize proteins.
Explanation: Correct: As Lactobacillus ferments sugars, it produces lactic acid, which is released into the medium. In an unbuffered medium, this acid accumulation will rapidly decrease the pH. Even though Lactobacillus is acid-tolerant, the pH will eventually drop below the minimum required for growth, inhibiting the cell's own enzymes and halting growth long before nutrients are depleted. This phenomenon is known as self-limiting growth. A: The opposite is true; the lack of a buffer will limit the final density. B: While tolerant of acid, Lactobacillus can typically initiate growth at neutral pH. D: The primary metabolism is fermentation of carbohydrates to acid, which will decrease, not increase, the pH.

Question 20

Two cultures of a mesophilic bacterium are grown to stationary phase in identical media. Culture A is incubated at its optimal temperature of 37°C, while Culture B is incubated at a suboptimal temperature of 25°C. How will the physiology of the cells entering the death phase likely differ between the two cultures?

  1. Cells from Culture B will have a lower endogenous metabolic rate and will remain viable for a longer period. (correct answer)
  2. Cells from Culture A will enter the death phase later due to a more efficient accumulation of storage granules.
  3. Both cultures will have identical rates of viability loss, as cell death is primarily caused by nutrient depletion.
  4. Cells from Culture B will lyse more quickly due to prolonged exposure to suboptimal cold temperatures.
Explanation: Correct: The death phase is characterized by a net loss of viable cells, often due to the depletion of internal energy reserves (endogenous metabolism) and accumulation of toxic byproducts. At a lower temperature (25°C), all metabolic reactions, including these self-destructive ones, proceed more slowly. This lower metabolic rate conserves energy and prolongs the period of viability compared to cells at the optimal temperature (37°C), where reserves are consumed much more quickly. B: Cells at the optimal temperature will deplete resources and reach the death phase faster. C: The rate of viability loss is temperature-dependent. D: 25°C is suboptimal for a mesophile, but it is not a lethal cold shock temperature; it will slow down, not accelerate, cell death.