1.5 The Nitrogen Cycle

Denitrification

Denitrifying bacteria change nitrate (NO3) into atmospheric nitrogen (N2) that returns to the atmosphere in a process called denitrification. The overall effect of denitrification is to return nitrogen to the atmosphere.

Sedimentation

In oceans, cyanobacteria change atmospheric nitrogen (N2) into ammonium (NH4) and then the ammonium can settle into sediments at the bottom of the ocean. This process is called sedimentation. The overall effect of sedimentation is to remove nitrogen from the cycle.

Nitrification

Lightning in the atmosphere can change atmospheric nitrogen (N2) directly into nitrate (N3) in a process called nitrification. The overall effect of nitrification is to change nitrogen into a form that is useable by plants.

Nitrogen Fixation

Nitrogen-fixing bacteria change atmospheric nitrogen (N2) into ammonium (NH4) in a process called nitrogen fixation. Nitrifying bacteria continue the nitrogen fixation process by turning the ammonium (NH4) into nitrous oxide (NO2) which then transforms into nitrate (NO3). The overall effect of nitrogen fixation is the removal of nitrogen from the atmosphere.

Excretion

Some nitrogen-based compounds are released back into the environment as waste products during excretion. The overall effect of excretion is to return nitrogen to the cycle.

Uptake

The process by which plants absorb nitrate (NO3) formed through either nitrogen fixation or nitrification to be used in their biological processes. Plants then use the nitrogen to create proteins and nucleic acids. Animals then eat the plants to get nitrogen for their bodies.

Decomposition

When organisms die, bacteria break down their bodies into compounds to return to the environment in a process called decomposition. The overall effect of decomposition is to return nitrogen to the cycle.