Increasing atmospheric carbon dioxide is
A) increasing sedimentation of C, Ca, and Si.
B) increasing the effect of the biological pump.
C) fueling increased primary production in ocean waters.
D) acidifying the ocean and decreasing the rate of formation of calcareous shells.
Coccolithophores and foraminiferans both use ________ to form their exoskeletons.
A) Si4+
B) Fe3+
C) Ca2+
D) HPO4-
Studying the redox cycling of Fe in the environment has led to the discovery
A) of bacteria that transfer electrons long distances and generate electric currents.
B) of bacteria that destroy toxic metal ions.
C) of archaea that have Fe in their cell walls.
D) that Fe limits primary production in terrestrial ecosystems.
Nitrogen fixation results in the
A) loss of biologically available N from an ecosystem.
B) formation of nitrogen gas.
C) direct formation of nitrate.
D) addition of biologically available N to an ecosystem.
Sulfide is toxic to respiring organisms, because it can combine with metals present in ________ that serve a critical function in respiration.
A) glycolysis enzymes
B) oxidases
C) NADH
D) cytochromes
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