why are bacteria a necessary part of the nitrogen cycle?\nother living things cannot use atmospheric…

Answer:

Other living things cannot use atmospheric nitrogen.

Brief Explanations:

In the nitrogen cycle, bacteria play a crucial role. Atmospheric nitrogen ($N_2$) is abundant but most organisms (like plants, animals) cannot directly use it. Bacteria, such as nitrogen - fixing bacteria, convert $N_2$ into ammonia ($NH_3$) or other forms (nitrification by other bacteria further converts ammonia to nitrates) that plants can absorb. Other options are incorrect: plants get nitrogen from soil (after bacterial conversion), the main nitrogen reservoir is the atmosphere, and bacteria are not nitrogen transpirators (transpiration is related to water loss in plants).