Question 1

Which of the following best describes the 'Great Plate Count Anomaly' in microbial ecology?

Accepted Answer

The observation that most microbes in environmental samples cannot be cultured using standard laboratory techniques.

Question 2

Which cultivation-independent technique is most commonly used to assess microbial community composition and diversity?

Accepted Answer

16S rRNA gene census

Question 3

In the context of sulfate reduction, which of the following equations correctly represents lactate oxidation coupled to sulfate reduction?

Accepted Answer

$$\mathrm{C_3H_5O_3^- + 1.75\ SO_4$^{2-} \rightarrow 3HCO_3^- + 1.75\ HS^- + 0.25\ H^+}$$

Question 4

Why are 'killed' controls (e.g., formalin-treated samples) important in bulk community activity measurements?

Accepted Answer

They help distinguish biological activity from abiotic chemical reactions.

Question 5

Which method allows for the detection and quantification of specific phylogenetic groups in a microbial community using fluorescently-labeled probes?

Accepted Answer

Fluorescence in situ hybridization (FISH)

Question 6

What is the main advantage of using stable isotope probing (SIP) in microbial ecology?

Accepted Answer

It links metabolic activity to specific organisms by tracking incorporation of labeled isotopes into biomolecules.

Question 7

Which chemical assay would be most appropriate for measuring the removal of lactate during sulfate reduction in an environmental sample?

Accepted Answer

Gas chromatography (GC-FID)

Question 8

A researcher wants to measure the rate of glucose respiration in a soil sample. Which of the following approaches would best allow them to distinguish between biological and abiotic CO$$_2$$ production?

Accepted Answer

Compare CO$$_2$$ evolution in live samples and formalin-killed controls using $$^{14}C-$$glucose.

Question 9

Which equation correctly represents aerobic glucose respiration?

Accepted Answer

$$\mathrm{C_6H_{12}O_6$ + 6O_2 \rightarrow 6CO_2 + 6H_2O}$$

Question 10

Which of the following statements about Fick's First Law is correct?

Accepted Answer

It describes the diffusion flux ($$J) as $$proportional to the concentration gradient, given by $$J = -D \frac{dC}{dx}.$$

Question 11

Which technique allows for visualization of spatial relationships and calculation of cell-specific metabolic rates by combining radioisotope labeling and microscopy?

Accepted Answer

FISH-microautoradiography (FISH-MAR)

Question 12

Isotopic fractionation in microbial processes provides information about:

Accepted Answer

The metabolic pathways and enzymes involved, based on preferential use of certain isotopes.

Question 13

Which of the following is a key reason why 16S rRNA is a particularly useful biomarker in microbial ecology?

Accepted Answer

It is highly conserved across all domains of life, allowing for phylogenetic identification.

Question 14

A scientist uses a microelectrode to measure oxygen concentration at different depths in a sediment core. What is the main advantage of this approach?

Accepted Answer

It provides high spatial resolution of chemical gradients, allowing inference of microbial guild locations.

Question 15

Which of the following best describes the principle of stable isotope probing (SIP)?

Accepted Answer

Microbes incorporate a stable isotope-labeled substrate into their DNA, which can then be separated and analyzed.

Question 16

Which of the following is NOT a cultivation-independent technique for studying microbial communities?

Accepted Answer

Serial dilution plating

Question 17

In a FISH experiment, what is the role of the fluorescently-labeled oligonucleotide probe?

Accepted Answer

It binds to a complementary sequence in the 16S rRNA, allowing visualization of specific microbial groups.

Question 18

Which of the following best explains why environmental transcriptomics and proteomics do not provide direct evidence of microbial activity?

Accepted Answer

Transcription and translation are regulated and may not always reflect actual metabolic activity.

Question 19

Which of the following statements about isotopic fractionation is correct?

Accepted Answer

Different enzymes and pathways impart distinct fractionation patterns, which can be used to infer metabolic processes.

Cultivation-Independent Methods in Microbial Ecology: Microbial Activities

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