35. Soil

Why do plants need nitrogen?

Which of the following is one of the key components of the nitrogen cycle?

In the context of nitrogen fixation, where is the majority of nitrogen stored in the Earth's ecosystem?

Which of the following is most directly responsible for nitrogen fixation?

Which of the following is primarily responsible for converting atmospheric nitrogen ($N_2$) into a form usable by plants and animals?

Why is nitrogen fixation an essential process in ecosystems?

Why do plants require assistance in converting atmospheric $\mathrm{N_2}$ into a usable form, and which organisms typically provide this help?

What is the primary use of nitrogen in living things?

Why is nitrogen fixation necessary for most living organisms?

How must carnivores obtain their nitrogen?

Which organisms are most critical in the nitrogen cycle due to their ability to fix atmospheric nitrogen?

Which of the following pathways indicates how nitrogen is added to the largest nitrogen reservoir (the atmosphere)?

How do animals and humans obtain usable nitrogen for their bodies?

Nitrogen gas ($N_2$) becomes converted into biologically usable chemical forms by what type of organism?

What role can lightning play in the nitrogen cycle?