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Quizzes > Science

The term facultative refers to what? Microbiology quiz

Quick, free quiz on facultative meaning in microbiology. Instant results.

Editorial: Review CompletedCreated By: Miss FallonUpdated Aug 24, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art microbes and growth curve icons on golden yellow background for facultative anaerobes and growth phases quiz

Use this quiz to check your understanding of the term facultative in microbiology and how facultative anaerobes grow in oxygen and without it through lag, log, stationary, and death phases. Keep learning with fastidious meaning in microbiology, brush up on cellular respiration basics, or test yourself with a clinical microbiology quiz.

What best describes a facultative anaerobe?
An organism that can grow with or without oxygen
An organism that only grows in the presence of oxygen
An organism that requires low levels of oxygen
An organism that only grows in the absence of oxygen
Facultative anaerobes are organisms capable of growing in both the presence and absence of oxygen, switching between aerobic respiration and anaerobic pathways as needed. They prefer oxygen because it yields more ATP but can ferment or respire anaerobically when oxygen is limited. This versatility differentiates them from obligate aerobes or anaerobes.
Which of the following bacteria is a well-known facultative anaerobe?
Pseudomonas aeruginosa
Bacteroides fragilis
Clostridium botulinum
Escherichia coli
Escherichia coli is a classic example of a facultative anaerobe that grows via aerobic respiration when oxygen is available and switches to fermentation or anaerobic respiration when it is not. Clostridium species are obligate anaerobes, Bacteroides are mostly strict anaerobes, and Pseudomonas is an obligate aerobe.
When oxygen is present, facultative anaerobes preferentially carry out which metabolic process?
Photosynthesis
Anaerobic respiration
Fermentation
Aerobic respiration
Facultative anaerobes preferentially use aerobic respiration when oxygen is available because it produces more ATP per glucose molecule. Fermentation and anaerobic respiration are used when oxygen is limited or absent. Photosynthesis is not a metabolic pathway used by these heterotrophic bacteria.
Under anaerobic conditions, facultative anaerobes most commonly switch to:
Oxidative phosphorylation
Chemolithotrophy
Photoautotrophy
Fermentation
When oxygen is absent, facultative anaerobes often resort to fermentation to regenerate NAD+ for glycolysis, producing byproducts like lactic acid, ethanol, or mixed acids. Oxidative phosphorylation requires a terminal electron acceptor such as oxygen. Photoautotrophy and chemolithotrophy are not typical fallback pathways for facultative anaerobes.
Which of the following best describes the term "anaerobe"?
An organism that does not require oxygen for growth
An organism that grows only at high oxygen concentrations
An organism that requires oxygen for growth
An organism that cannot survive in oxygen
An anaerobe is any organism that does not require oxygen for growth and may even be inhibited or killed by its presence. Obligate anaerobes cannot tolerate oxygen, while aerotolerant anaerobes tolerate but do not use oxygen. Facultative anaerobes are a subgroup that can grow with or without oxygen.
In thioglycollate broth, a facultative anaerobe will typically show:
Growth only at the top of the tube
Growth only at the bottom of the tube
Uniform growth throughout the tube
Growth predominantly at the surface with some throughout
Thioglycollate broth creates an oxygen gradient; facultative anaerobes grow throughout but are denser at the oxygen-rich surface where aerobic respiration yields more energy. Obligate aerobes remain at the top, and obligate anaerobes at the bottom.
What is the approximate ATP yield per glucose molecule in fermentation by facultative anaerobes like E. coli?
4 ATP
38 ATP
36 ATP
2 ATP
Fermentation yields only 2 ATP per glucose through substrate-level phosphorylation during glycolysis. Aerobic respiration can yield up to 38 ATP per glucose in prokaryotes. The low yield is why facultative anaerobes prefer oxygen when available.
During which growth phase do facultative anaerobes typically induce genes for anaerobic metabolism after oxygen depletion?
Exponential (log) phase
Death phase
Lag phase
Stationary phase
When facultative anaerobes face a drop in oxygen, they enter an extended lag phase to synthesize enzymes and regulators for anaerobic metabolism before exponential growth resumes. The log phase follows once metabolic adjustments are complete.
Which global regulator protein activates anaerobic respiration genes in Escherichia coli when oxygen is limited?
LacI
Sigma 32
CRP
FNR
FNR (fumarate and nitrate reduction regulator) senses oxygen levels via an iron-sulfur cluster and activates anaerobic respiration genes under low oxygen. CRP responds to cAMP and catabolite repression, LacI controls lactose metabolism, and Sigma 32 is a heat-shock sigma factor.
In the presence of nitrate as an electron acceptor, facultative anaerobes can perform:
Nitrogen fixation
Sulfur oxidation
Oxygenic photosynthesis
Denitrification
Facultative anaerobes can switch to anaerobic respiration using nitrate as a terminal electron acceptor, reducing it to nitrite or further to nitrogenous gases (denitrification). Oxygenic photosynthesis, sulfur oxidation, and nitrogen fixation are different processes not typically performed by these bacteria.
What does the Pasteur effect describe in facultative anaerobes?
Switch from fermentation to photosynthesis
Stimulation of fermentation by oxygen
Inhibition of fermentation by oxygen
Production of ethanol under aerobic conditions
The Pasteur effect is the inhibition of fermentation pathways by oxygen; facultative anaerobes slow down or stop fermentative metabolism when oxygen is present to favor more efficient aerobic respiration.
Which major end product is produced by lactic acid bacteria during fermentation?
Butyric acid
Lactic acid
Acetic acid
Ethanol
Lactic acid bacteria convert sugars predominantly into lactic acid via homolactic or heterolactic fermentation pathways. Acetic acid and ethanol are produced by other fermenters, and butyric acid is typical of Clostridium species.
A facultative anaerobe with a doubling time of 20 minutes will increase from 1 to how many cells in one hour during exponential growth?
16
8
4
6
In one hour (60 minutes), 20-minute doubling yields three generations: 2^3 = 8 cells starting from one. Each doubling multiplies the population by two.
Which enzyme catalyzes the conversion of pyruvate to lactate in facultative anaerobes?
Pyruvate decarboxylase
Pyruvate oxidase
Lactate dehydrogenase
Alcohol dehydrogenase
Lactate dehydrogenase reduces pyruvate to lactate under anaerobic conditions, regenerating NAD+ for glycolysis. Pyruvate decarboxylase and alcohol dehydrogenase are involved in ethanol fermentation, while pyruvate oxidase functions aerobically.
How does midpoint redox potential (E°') influence electron acceptor usage in facultative anaerobes?
Midpoint potential has no effect on respiratory choice
Higher potential acceptors yield less ATP
Acceptors with higher E°' are preferred under aerobic conditions
Only low potential acceptors can be used
Electron acceptors with higher redox potentials (like oxygen) yield more energy per electron transferred and are preferentially used when available. Under anaerobic conditions, facultative anaerobes resort to acceptors with lower E°' such as nitrate or sulfur compounds.
What is the primary role of the ArcA regulator in E. coli under anaerobic conditions?
Bind lactose operon promoter
Activate TCA cycle genes
Increase cyclic AMP levels
Repress aerobic respiration genes
ArcA, part of the ArcAB two-component system, is phosphorylated under low oxygen and represses genes involved in aerobic respiration, shifting metabolism to anaerobic pathways. It also activates some fermentative genes.
In fermentative metabolism, a high NAD+/NADH ratio indicates:
Overflow of NADH
Unbalanced ATP production
Complete inhibition of glycolysis
Efficient NADH oxidation
A high NAD+/NADH ratio means NADH is being oxidized back to NAD+ efficiently, allowing glycolysis to continue under fermentative conditions. If NADH accumulates, the ratio drops and glycolysis stalls.
What causes diauxic growth when a facultative anaerobe is grown in medium with glucose and lactose?
Protein denaturation in mid-exponential phase
pH drop inhibiting enzyme function
Oxygen depletion halfway through growth
Sequential sugar utilization due to catabolite repression
Diauxic growth occurs because glucose is consumed first, and only after its depletion is the lac operon derepressed to allow lactose metabolism. This sequential utilization is regulated by catabolite repression via cAMP-CRP.
Which technique measures real-time oxygen consumption rates in facultative anaerobic cultures?
Spectrophotometry at 600 nm
qPCR of respiratory genes
Mass spectrometry of CO2
Clark-type oxygen electrode
A Clark-type oxygen electrode directly measures dissolved oxygen consumption by cells in real time, allowing calculation of respiratory rates. Spectrophotometry tracks cell density, qPCR measures gene expression, and CO2 measurement doesn't directly indicate O2 usage.
How does the P/O ratio of ATP production change when facultative anaerobes perform anaerobic respiration compared to aerobic respiration?
It remains the same
It decreases during anaerobic respiration
It increases during anaerobic respiration
It drops to zero
The P/O ratio (ATP per oxygen atom) is lower in anaerobic respiration because alternative electron acceptors yield less proton motive force than oxygen. Thus, fewer ATP molecules are synthesized per electron transferred.
Which sigma factor is upregulated in facultative anaerobes during stationary phase to promote stress survival?
Sigma 70
Sigma 32
Sigma S (RpoS)
Sigma 54
Sigma S (RpoS) is a stress-response sigma factor that directs RNA polymerase to genes needed for stationary-phase survival and general stress resistance in many bacteria, including facultative anaerobes. Sigma 70 is the housekeeping factor, Sigma 32 responds to heat shock, and Sigma 54 regulates nitrogen metabolism.
At low oxygen tensions, which cytochrome oxidase is primarily used by E. coli?
Cytochrome bd oxidase
Cytochrome aa3 oxidase
Cytochrome bo3 oxidase
Cytochrome c oxidase
E. coli expresses cytochrome bd oxidase under microaerobic or low-oxygen conditions because it has higher affinity for oxygen, allowing respiration even when O2 is scarce. Cytochrome bo3 functions at higher oxygen levels.
Which small regulatory RNA in E. coli fine-tunes anaerobic gene expression by targeting fnr mRNA?
OmrA
FnrS
RyhB
Spot42
FnrS is a small RNA activated by FNR under anaerobic conditions and modulates the expression of numerous target mRNAs to fine-tune anaerobic metabolism. Spot42, RyhB, and OmrA regulate different stress responses or metabolic pathways.
In genome-scale flux balance analysis of facultative anaerobes under anaerobic simulations, which uptake rate is usually constrained to zero?
Nitrate uptake rate
Ammonia uptake rate
Glucose uptake rate
Oxygen uptake rate
To simulate anaerobic growth in flux balance analysis, the oxygen uptake rate is constrained to zero, representing the absence of molecular oxygen. Other nutrient uptakes like glucose or ammonia remain unconstrained to allow growth predictions.
Which cofactor is essential for activation of pyruvate formate lyase (PFL) during fermentation in E. coli?
NAD+
Thiamine pyrophosphate
[4Fe-4S] cluster
Biotin
Activation of pyruvate formate lyase requires a specialized activating enzyme that uses S-adenosylmethionine to generate a glycyl radical, supported by a [4Fe-4S] cluster. This radical is critical for PFL's catalytic mechanism under anaerobic conditions.
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Study Outcomes

  1. Define facultative anaerobe -

    Explain that the term facultative anaerobe refers to an organism that can grow in both the presence and absence of oxygen.

  2. Distinguish anaerobic vs aerobic bacteria -

    Compare and contrast bacterial growth requirements under oxygen-rich and oxygen-depleted conditions.

  3. Describe microbial growth phases -

    Outline the lag, log, stationary, and death phases to understand bacterial population dynamics.

  4. Assess bacterial growth conditions -

    Apply knowledge of environmental factors to predict optimal growth scenarios for different microbes.

  5. Analyze quiz results -

    Interpret your score to identify strengths and areas for further study in microbial growth concepts.

Cheat Sheet

  1. Facultative Anaerobe Definition -

    the term facultative anaerobe refers to an organism that can thrive with or without oxygen by toggling between aerobic respiration and anaerobic fermentation. This metabolic flexibility sets facultative anaerobes apart from strict aerobes or anaerobes (ASM Microbe Library).

  2. Metabolic Pathways -

    Facultative anaerobes use the electron transport chain when O₂ is present and switch to pathways like lactic acid or ethanol fermentation under anaerobic conditions (Journal of Bacteriology). Remember "F for Flexible" to recall their dual pathways.

  3. Microbial Growth Phases -

    In a microbial growth phases quiz, you'll identify lag, exponential, stationary, and death phases. The formula Nt = N₀×2❿ helps calculate cell numbers during log phase - key for understanding how facultative anaerobes ramp up population under ideal conditions (Microbiology Society).

  4. Aerobic vs Anaerobic Bacteria -

    Comparing anaerobic vs aerobic bacteria, facultative anaerobes bridge both worlds: they can detoxify reactive oxygen species like aerobes yet ferment like anaerobes. This dual nature influences their preferred bacterial growth conditions, from oxygen-rich skin surfaces to oxygen-poor gut environments (CDC).

  5. Clinical and Environmental Relevance -

    Many pathogens like E. coli and Salmonella are facultative anaerobes, exploiting both niches during infection. Their adaptability under varying oxygen tensions makes them robust in diverse settings - from water treatment to the human intestine.

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