Nitrogen moves from the atmosphere, to organisms, and back to the atmosphere in the nitrogen cycle. 21 __ is the process by which bacteria turn nitrogen gas nds plants can use.

<p> The question refers to the portion of the nitrogen cycle where nitrogen is made usable for other organisms. Specifically, it is asking about the process in which bacteria convert gaseous nitrogen into nitrogen compounds that can be absorbed and used by plants. This is a basic principle in biology, found especially within the scope of ecosystem interactions and nutrient cycles. The process is crucial for life because nitrogen in its gaseous form (N2) is unusable for most living organisms, but when it's transformed into compounds such as ammonia (NH3) or nitrate (NO3-), it can be utilized by plants and subsequently enter the food chain.</p>