Question 1

Which of the following best describes the primary ecological function of biofilms in natural environments?

Accepted Answer

They allow bacteria to remain in favorable niches, resist environmental stresses, and facilitate nutrient and genetic exchange.

Question 2

A researcher is studying a freshwater lake that experiences seasonal stratification. During the summer, the bottom waters become anoxic. Which process is most likely to increase in the hypolimnion under these conditions?

Accepted Answer

Anaerobic respiration and fermentation by microorganisms

Question 3

Which of the following statements about the legume–root nodule symbiosis is correct?

Accepted Answer

Leghemoglobin in the nodule maintains low free oxygen concentrations, protecting nitrogenase from inactivation.

Question 4

A soil sample is analyzed using 16S rRNA gene sequencing. The results show a high diversity of Proteobacteria, Acidobacteria, and Actinobacteria. What does this indicate about the soil environment?

Accepted Answer

The soil contains numerous microenvironments supporting diverse metabolic types.

Question 5

Which of the following is a key adaptation that allows Pelagibacter to thrive in oligotrophic marine environments?

Accepted Answer

A high surface-to-volume ratio and numerous ABC-type transporters for efficient nutrient uptake

Question 6

Which of the following best explains why biofilm-associated bacteria are often more resistant to antibiotics than planktonic bacteria?

Accepted Answer

Biofilms slow the penetration of antibiotics and promote the expression of stress-tolerance genes.

Question 7

In the mutualistic consortium 'Chlorochromatium aggregatum', what is the primary metabolic relationship between the green sulfur bacterial epibionts and the central rod-shaped bacterium?

Accepted Answer

The epibionts perform photosynthesis and supply organic matter to the central chemotrophic bacterium.

Question 8

Which of the following statements about arbuscular mycorrhizae (AM) is correct?

Accepted Answer

AM fungi transfer inorganic nutrients such as phosphorus and nitrogen to the plant in exchange for carbohydrates.

Question 9

A scientist is using fluorescence in situ hybridization (FISH) to study a microbial community. What is the main advantage of FISH over traditional staining methods?

Accepted Answer

FISH can reveal the phylogenetic identity of microorganisms in situ.

Question 10

Which of the following best describes the role of auxiliary metabolic genes (AMGs) in marine viruses?

Accepted Answer

AMGs alter host metabolism to maximize viral replication, often supplementing host metabolic pathways.

Question 11

Which of the following is a major ecological consequence of the destruction of biological soil crusts (BSCs) in arid environments?

Accepted Answer

Increased soil erosion and reduced water infiltration

Question 12

A lake receives a large input of organic matter from agricultural runoff, resulting in a high biochemical oxygen demand (BOD). What is the most likely immediate effect on the lake's oxygen levels?

Accepted Answer

Dissolved oxygen levels will decrease due to increased microbial respiration.

Question 13

Which of the following statements about microbial mats is correct?

Accepted Answer

Microbial mats are thick, layered biofilms composed of different microbial guilds, often found in extreme environments.

Question 14

Which of the following is a defining feature of oligotrophic bacteria such as Pelagibacter in the open ocean?

Accepted Answer

They grow best at very low concentrations of nutrients and have highly efficient nutrient uptake systems.

Question 15

Which of the following best explains the ecological importance of viruses in marine environments?

Accepted Answer

They mediate the transfer of organic carbon and genes, influence microbial diversity, and regulate nutrient cycling.

Question 16

A researcher is studying a deep-sea bacterium that grows optimally at 700 atm and 6°C. Which term best describes this organism?

Accepted Answer

Hyperpiezophilic psychrophile

Question 17

Which of the following statements about the diversity of Archaea in soils is correct?

Accepted Answer

Archaeal diversity is low, but some groups, such as Thaumarchaeota, are abundant and play key roles in nitrification.

Question 18

Which of the following is a key difference between ectomycorrhizae and arbuscular mycorrhizae (AM)?

Accepted Answer

Ectomycorrhizae form a sheath around roots and penetrate only slightly, while AM fungi form arbuscules deeply embedded within root cells.

Question 19

Which of the following best describes the function of quorum sensing in bacterial biofilm formation?

Accepted Answer

It coordinates gene expression in response to cell density, regulating biofilm development and virulence.

Microbial Ecology: Diversity, Symbiosis, and Environmental Interactions

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