Question 1

Which of the following statements best describes the main ecological role of Pelagibacter in marine environments?

Accepted Answer

It is an extremely small, abundant microorganism that plays a significant role in the Earth's carbon cycle.

Question 2

Which of the following bacteria is responsible for converting ammonium ions ($$NH_4$$^+$$) to nitrite (NO_2$^-) in $$the nitrogen cycle?

Accepted Answer

Nitrosomonas

Question 3

A patient presents with a high fever, muscle aches, and a dry cough after working with livestock. Which bacterium is most likely responsible for these symptoms, and how is it typically transmitted?

Accepted Answer

Coxiella burnetii; transmitted via aerosols or milk from infected animals

Question 4

Which of the following best explains why Chlamydia species are considered obligate intracellular pathogens?

Accepted Answer

They require host cell machinery to reproduce and form infectious elementary bodies.

Question 5

Which of the following bacteria is associated with the formation of crown gall tumors in plants, and what is the mechanism?

Accepted Answer

Agrobacterium; inserts a plasmid into plant cells, inducing tumor formation

Question 6

Which of the following is a distinguishing feature of Spirochaetes, such as Treponema pallidum?

Accepted Answer

They move using axial filaments that create a corkscrew motion.

Question 7

Which of the following equations correctly represents the oxidation of hydrogen sulfide by Acidithiobacillus?

Accepted Answer

$$H_2S + 2O_2 \rightarrow SO_4$^{2-} + 2H^+$$

Question 8

Which of the following best describes the difference between oxygenic and anoxygenic photosynthetic bacteria?

Accepted Answer

Oxygenic bacteria use $$H_2O as an $$electron donor and produce $$O_2$$; anoxygenic bacteria use compounds like $$H_2S$$ and do not produce $$O_2.$$

Question 9

A hospital outbreak of urinary tract infections is traced to a bacterium with peritrichous flagella and swarming motility. Which genus is most likely responsible?

Accepted Answer

Proteus

Question 10

Which of the following is a unique characteristic of Archaea compared to Bacteria?

Accepted Answer

Archaea can thrive in extreme environments such as high salt, high temperature, or low pH.

Question 11

Which of the following bacteria is most likely to be found in the human colon and is important for degrading cellulose and chitin?

Accepted Answer

Bacteroides

Question 12

Which of the following best explains why Streptococcus and Clostridium are classified as low G+C Gram-positive bacteria?

Accepted Answer

Their DNA contains a low percentage of guanine and cytosine bases.

Question 13

Which of the following bacteria is responsible for causing whooping cough, and what is a distinguishing feature?

Accepted Answer

Bordetella pertussis; nonmotile rod

Question 14

Which of the following is a correct description of the life cycle of Chlamydia?

Accepted Answer

The elementary body is the infectious form that is released from host cells.

Question 15

Which of the following bacteria is most likely to cause peptic ulcers and stomach cancer, and what is a key feature of its motility?

Accepted Answer

Helicobacter pylori; multiple flagella

Question 16

Which of the following is a plausible method for detecting bacteria that cannot be cultured in the laboratory?

Accepted Answer

Using molecular techniques such as PCR to detect bacterial DNA sequences.

Question 17

Which of the following bacteria is a common cause of nosocomial infections and produces a characteristic red pigment?

Accepted Answer

Serratia marcescens

Question 18

Which of the following best describes the role of methanogenic archaea in the human microbiota?

Accepted Answer

They produce methane as a metabolic byproduct in anaerobic environments such as the colon.

Question 19

Which of the following bacteria is transmitted by fleas and is responsible for causing plague?

Accepted Answer

Yersinia pestis

Question 20

Which of the following is a correct pairing of a bacterium and the disease it causes?

Accepted Answer

Treponema pallidum – syphilis

The Prokaryotes: Domains Bacteria and Archaea – Classification, Structure, and Diversity

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