Refer to the figure. Based on the diagram, the process most responsible for returning nitrogen to the atmosphere as a gas is
A) bacterial nitrogen fixation.
B) nitrification.
C) nitrate reduction.
D) denitrification.
E) industrial nitrogen fixation.

Question

Refer to the figure.  Based on the diagram, the process most responsible for returning nitrogen to the atmosphere as a gas is
A) bacterial nitrogen fixation. 
B) nitrification. 
C) nitrate reduction. 
D) denitrification. 
E) industrial nitrogen fixation.

Quizplus · Accepted Answer

The process most responsible for returning nitrogen to the atmosphere as a gas is denitrification, which is shown in the figure as step 4. Denitrification is carried out by denitrifying bacteria that convert nitrate (NO3-) into nitrogen gas (N2) which is released into the atmosphere. Bacterial nitrogen fixation (choice A) and industrial nitrogen fixation (choice E) add nitrogen to the ecosystem, while nitrification (choice B) and nitrate reduction (choice C) convert nitrogen into forms that can be used by plants but do not release nitrogen as a gas into the atmosphere.

Refer to the Figure