Bacteria able to perform the NH4+ + NO2− → N2 + 2H2O reaction have been discovered in laboratory bioreactors and wastewater treatment systems. Researchers predicted that these bacteria should exist in oceans. They measured the concentration of NH4+, NO2−, NO3−, and O2 in the Black Sea as a function of water depth (M. Kuypers et al. 2003 Anaerobic ammonium oxidation by anammox bacteria in the Black Sea. Nature 422:608-11) to determine where in the sea the bacteria might live. By analyzing data presented in the accompanying figure, at what depth would you expect to find the bacteria? (Note: In the figure, different scales are used to show concentrations of NH4+, NO2−, NO3−, and O2.)
A) in the top 5 meters
B) in the top 50 meters
C) at a depth of 75 meters
D) at a depth of 92 meters
E) below 100 meters

Question

Bacteria able to perform the NH4+ + NO2− → N2 + 2H2O reaction have been discovered in laboratory bioreactors and wastewater treatment systems. Researchers predicted that these bacteria should exist in oceans. They measured the concentration of NH4+, NO2−, NO3−, and O2 in the Black Sea as a function of water depth (M. Kuypers et al. 2003 Anaerobic ammonium oxidation by anammox bacteria in the Black Sea. Nature 422:608-11) to determine where in the sea the bacteria might live. By analyzing data presented in the accompanying figure, at what depth would you expect to find the bacteria? (Note: In the figure, different scales are used to show concentrations of NH4+, NO2−, NO3−, and O2.)
A) in the top 5 meters 
B) in the top 50 meters 
C) at a depth of 75 meters 
D) at a depth of 92 meters 
E) below 100 meters

Quizplus · Accepted Answer

In the figure, we can see that the concentration of both NH4+ and NO2− decreases rapidly at a depth of around 80 meters. This suggests that these substances are being consumed by bacteria (such as anammox bacteria) at this depth. Therefore, we would expect to find the bacteria performing the NH4+ + NO2− → N2 + 2H2O reaction at a depth of around 80 meters, which corresponds to answer choice D (at a depth of 92 meters).

Bacteria Able to Perform the NH4+ + NO2− → N2