Question 1

Which of the following best describes the main anthropogenic (human-generated) source of sulfur pollution in the environment?

Accepted Answer

Combustion of fossil fuels

Question 2

In the sulfur cycle, which oxidation state is associated with sulfate ($$SO_4$$^{2-}$$)?

Accepted Answer

$$+6$$

Question 3

Why do oxidized forms of sulfur dominate in oxic environments, while reduced forms dominate in anoxic environments?

Accepted Answer

Because oxygen is a strong electron acceptor, favoring oxidation in oxic environments

Question 4

Which of the following is the correct sequence of intermediates in the dissimilatory sulfate reduction pathway?

Accepted Answer

Sulfate $$\rightarrow$$ APS $$\rightarrow$$ Sulfite $$\rightarrow$$ Sulfide

Question 5

A sample containing $$SO_4$$^{2-}$$ and an electron donor is incubated with a sulfate-reducing bacterium. Which of the following products would you expect to measure to confirm sulfate reduction?

Accepted Answer

Production of $$H_2S$$

Question 6

Which gene is commonly used as a biomarker for identifying sulfate-reducing bacteria in environmental samples?

Accepted Answer

dsrAB

Question 7

Which of the following best explains why most known iron-oxidizing bacteria are acidophiles?

Accepted Answer

Abiotic oxidation of $$Fe^{2+} is $$slow at low pH, allowing bacteria to compete for $$Fe^{2+} as an $$energy source

Question 8

Which of the following reactions represents the oxidation of ferrous iron ($$Fe^{2+}) by $$oxygen in acid mine drainage?

Accepted Answer

$$Fe^{2+}$$ + \frac{1}{2}$$O_2$$ + \frac{3}{2}H_2O \rightarrow FeO(OH) + 2H^+$$

Question 9

A bioremediation project aims to immobilize uranium in groundwater. Which microbial process is most relevant for this application?

Accepted Answer

Reduction of $$U^{6+} to$$ $$U^{4+} by $$iron-reducing bacteria

Question 10

Which of the following is a major reason why sulfate reducers are typically strict anaerobes?

Accepted Answer

Oxygen is a more favorable terminal electron acceptor than sulfate

Question 11

Which of the following best describes the role of ATP sulfurylase in sulfate reduction?

Accepted Answer

It activates sulfate by converting it to APS (adenosine 5'-phosphosulfate)

Question 12

In the context of sulfur-based chemolithotrophy, which of the following is a correct oxidation reaction for hydrogen sulfide ($$H_2S$$)?

Accepted Answer

$$H_2S + \frac{1}{2}O_2$ \rightarrow S^0$ + H_2O$$

Question 13

Which of the following is a key difference between assimilatory and dissimilatory sulfate reduction?

Accepted Answer

Assimilatory reduction incorporates sulfur into biomass, while dissimilatory reduction uses sulfate as a terminal electron acceptor

Question 14

Which of the following best explains why the redox state of an element affects its solubility and transport in the environment?

Accepted Answer

Different redox states have different chemical properties, influencing their solubility and mobility

Question 15

Which of the following is a correct description of the role of rusticyanin in iron-oxidizing bacteria?

Accepted Answer

It removes electrons from $$Fe^{2+}$$ and transfers them to cytochromes in the electron transport chain

Question 16

A marine sediment sample is found to contain high levels of Desulfovibrio species. Which metabolic process is most likely occurring in this environment?

Accepted Answer

Dissimilatory sulfate reduction

Question 17

Which of the following is a real-world consequence of acid mine drainage caused by microbial iron oxidation?

Accepted Answer

Formation of acidic waters and precipitation of ferric iron minerals

Question 18

Which of the following best describes the function of DMSP (dimethylsulfoniopropionate) in the marine sulfur cycle?

Accepted Answer

It is produced by marine algae and can be converted to DMS (dimethylsulfide), which enters the atmosphere

Question 19

Which of the following equations represents the reduction of ferric iron ($$Fe^{3+}) by $$acetate in anoxic conditions?

Accepted Answer

$$CH_3COO^- + 8Fe$$^{3+}$$ + 4H_2O \rightarrow 2HCO_3^- + 8Fe$$^{2+}$$ + 9H^+$$

Sulfur and Iron Biogeochemical Cycles: Microbial Roles and Environmental Impact

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