AP BIOLOGY

Detailed explanation-1: -Denitrifying bacteria convert the nitrate back into nitrogen gas, which reenters the atmosphere. Nitrogen from runoff and fertilizers enters the ocean, where it enters marine food webs. Some organic nitrogen falls to the ocean floor as sediment.

Detailed explanation-2: -Nitrogen is returned to the atmosphere by the activity of organisms known as decomposers. Some bacteria are decomposers and break down the complex nitrogen compounds in dead organisms and animal wastes.

Detailed explanation-3: -Denitrifying bacteria use all three energy sources available to bacteria including organic carbon compounds (organotrophs), inorganic compounds (lithotrophs), and light (phototrophs). The dominant populations of denitrifiers appear to be organotrophs such as Pseudomonas and Alcaligenes.

Detailed explanation-4: -Denitrifiers are chemoorganotrophs and thus must also be supplied with some form of organic carbon. Denitrification is important in that it removes fixed nitrogen (i.e., nitrate) from the ecosystem and returns it to the atmosphere in a biologically inert form (N2).

Detailed explanation-5: -denitrifying bacteria, microorganisms whose action results in the conversion of nitrates in soil to free atmospheric nitrogen, thus depleting soil fertility and reducing agricultural productivity.