Question 1

Which of the following best describes an oligotrophic environment?

Accepted Answer

An environment with low nutrient levels, where most microbes inhabit.

Question 2

What is the primary function of morphological changes such as endospore formation in microbes?

Accepted Answer

To survive starvation and environmental stress.

Question 3

Which of the following is NOT a consequence of biofilm formation?

Accepted Answer

Increased susceptibility to antibiotics.

Question 4

During biofilm formation, what is the role of the extracellular matrix?

Accepted Answer

It acts as a barrier to protect microbes from environmental stress.

Question 5

Quorum sensing in bacteria is best described as:

Accepted Answer

A process where bacteria communicate based on population density.

Question 6

Which molecule is the primary autoinducer in Gram-negative quorum sensing?

Accepted Answer

N-acyl homoserine lactone (AHL)

Question 7

In the symbiotic relationship between Rhizobium and legumes, what does the plant provide to the bacteria?

Accepted Answer

Sugars and nutrients

Question 8

Which equation correctly represents the nitrogen fixation reaction catalyzed by nitrogenase?

Accepted Answer

$$N_2 + 3H_2$$ \rightarrow 2NH_3$$

Question 9

Why is leghemoglobin important in root nodules?

Accepted Answer

It binds oxygen, protecting nitrogenase from inactivation.

Question 10

Which of the following statements about nitrogenase is TRUE?

Accepted Answer

It catalyzes the reduction of $$N_2 to$$ $$NH_3.$$

Question 11

How do free-living nitrogen-fixing bacteria like Azotobacter protect nitrogenase from oxygen?

Accepted Answer

By having a high rate of respiration to reduce oxygen levels.

Question 12

Which process is regulated by quorum sensing in Vibrio fischeri within the bobtail squid?

Accepted Answer

Bioluminescence

Question 13

What triggers the activation of nod genes in Rhizobium during nodule formation?

Accepted Answer

Release of flavonoids by root cells

Question 14

Which of the following is a mutualistic symbiotic interaction?

Accepted Answer

Rhizobium fixing nitrogen for legumes and receiving sugars in return

Question 15

Which of the following best explains why biofilms are more resistant to antibiotics than planktonic cells?

Accepted Answer

The extracellular matrix limits antibiotic penetration and facilitates gene exchange.

Question 16

A patient with a hip implant develops a persistent infection. Which microbial property is most likely responsible?

Accepted Answer

Formation of a biofilm on the implant surface

Question 17

Which of the following is a key feature of competent cells in Streptococcus pneumoniae?

Accepted Answer

Ability to take up DNA from the environment

Question 18

Which of the following is NOT a free-living nitrogen-fixing bacterium?

Accepted Answer

Rhizobium

Question 19

Which step in biofilm formation involves cell-to-cell signaling and onset of exopolymer production?

Accepted Answer

Cell-to-cell signaling and exopolymer production

Question 20

Why do microbes in stationary phase reduce in size and increase their surface area to volume ratio?

Accepted Answer

To become more efficient at nutrient transport under starvation

Microbial Growth in Natural Environments: Biofilms and Symbiotic Nitrogen Fixation

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