Exercises: The stages of the nitrogen cycle

Explain why plants cannot use nitrogen gas (N₂) from the atmosphere even though it is very abundant, and name the organisms that "fix" it by turning it into compounds that roots can absorb.

Order the following stages of the nitrogen cycle into a logical sequence and explain what happens in each one: denitrification, fixation, absorption by plants, decomposition of remains, nitrification.

In the Mexican milpa, corn, beans, and squash have been planted together for centuries. Beans, like other legumes, host nitrogen-fixing bacteria in their roots. Explain, using what you know about the nitrogen cycle, why corn grows better when planted next to beans.