Final answer:
The names of the two main processes that change atmospheric nitrogen into usable forms for other organisms are nitrogen fixation and denitrification. Nitrogen fixation is carried out by certain microorganisms that convert nitrogen gas into ammonia. Denitrification is the process that converts nitrates back into nitrogen gas.
Step-by-step explanation:
The Processes that Change Nitrogen into Usable Forms
The two main processes that transform atmospheric nitrogen into forms usable by other organisms in the nitrogen cycle are called nitrogen fixation and denitrification. During nitrogen fixation, certain microorganisms convert nitrogen gas (N2) from the atmosphere into ammonia (NH3), which can then be further processed into nitrates and nitrites that plants can absorb. In contrast, denitrification involves different microbes converting nitrates back into nitrogen gas, thus releasing it back into the atmosphere. This nitrogen gas can then continue the nitrogen cycle. Additionally, the process of nitrification, which converts ammonia into nitrites and nitrates, plays a crucial role in making nitrogen available to plants after nitrogen fixation has occurred.