Question

Which of the following locations is the main reservoir for nitrogen in Earth's nitrogen cycle?

-plant and animal biomass
-sedimentary bedrock
-fossilized plant and animal remains (coal, oil, and natural gas)
-atmosphere
-soil

Answer 1

The main reservoir for nitrogen in Earth's nitrogen cycle is the atmosphere. Air contains about 79% nitrogen gas (N2), but most organisms cannot use nitrogen in this form.

Step-by-step explanation:

The main reservoir for nitrogen in Earth's nitrogen cycle is the atmosphere.

Air contains about 79% nitrogen gas (N2), making it the largest pool of available nitrogen in terrestrial ecosystems. However, most organisms cannot use nitrogen in this form. Plants, for example, need to obtain nitrogen in fixed forms such as nitrate ions (NO3-) and ammonium ions (NH4+).

Therefore, while the atmosphere is the main reservoir for nitrogen, it must be converted into usable forms by nitrogen-fixing bacteria before it can be incorporated into the food webs of plants and animals.