Question 1

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

Accepted Answer

Many microbes in environmental samples do not grow under laboratory conditions, leading to plate counts that are much lower than direct microscopic counts.

Question 2

Why do microbial ecologists often seek to isolate pure cultures of microorganisms?

Accepted Answer

To enable reproducible experiments and unambiguous assignment of physiological properties to a single species.

Question 3

Which macronutrient is most commonly utilized by autotrophic microbes as an inorganic carbon source?

Accepted Answer

CO$$_2$$

Question 4

What is the primary advantage of using enrichment cultures in microbial ecology?

Accepted Answer

They select for microbes with specific metabolic traits by providing selective growth conditions.

Question 5

Which of the following is a reason why some microbes present in nature may not form colonies on laboratory plates?

Accepted Answer

They require syntrophic partners or specific growth conditions not provided in the lab.

Question 6

Which of the following statements about micronutrients in microbial nutrition is correct?

Accepted Answer

Micronutrients are typically present in the active site of enzymes or as cofactors.

Question 7

A researcher wants to isolate nitrogen-fixing bacteria from soil. Which enrichment strategy should they use?

Accepted Answer

Provide N$$_2 as $$the only nitrogen source and mannitol as the carbon source.

Question 8

Which of the following best describes a defined medium?

Accepted Answer

A medium where the exact chemical composition is known.

Question 9

What is the main purpose of using serial dilutions in microbial isolation?

Accepted Answer

To enumerate and isolate individual organisms by reducing cell density.

Question 10

Which historical figure is credited with pioneering the use of solid growth media for the isolation of pure cultures?

Accepted Answer

Robert Koch

Question 11

Which of the following is a plausible explanation for the discrepancy between plate counts and direct microscopic counts in oligotrophic environments?

Accepted Answer

Microbes in oligotrophic environments are more likely to be dormant or require specific partners for growth.

Question 12

Which of the following is NOT a typical source of nitrogen for microbial growth?

Accepted Answer

CO$$_2$$

Question 13

What is the role of agar in microbial cultivation?

Accepted Answer

It solidifies the medium, allowing for the formation of colonies from single cells.

Question 14

Which cultivation-dependent method is most suitable for isolating phototrophic bacteria from a mixed sample?

Accepted Answer

Agar shake tube technique

Question 15

Why is the use of pure cultures important for hypothesis testing in microbial ecology?

Accepted Answer

It provides a simplified system for reproducibility and experimental control.

Question 16

Which of the following is a key feature of the Winogradsky column?

Accepted Answer

It creates stratified microbial communities and microenvironments within a tube.

Question 17

Which of the following is a disadvantage of enrichment cultures?

Accepted Answer

They may introduce enrichment bias, favoring 'weeds' and not revealing the most abundant organisms.

Question 18

Which equation would you use to calculate the number of cells per mL in a dilution series if you plated 0.1 mL of a $$10^{-4}$$ dilution and counted 50 colonies?

Accepted Answer

$$\frac{	ext{Number of colonies}}{	ext{Volume plated (mL)}} 	imes 	ext{Dilution factor}$$

Question 19

Which of the following is a reason why some microbes require vitamins or growth factors from their environment?

Accepted Answer

They lack the metabolic pathways to synthesize certain essential compounds.

Question 20

Which cultivation-independent method is commonly used to analyze microbial community composition?

Accepted Answer

Genetic sequencing of environmental DNA

Cultivation-dependent Methods in Microbial Ecology: Principles, Techniques, and Applications

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