Nitrogen Cycle

“Air is rich in nitrogen, but most organisms cannot use it until other organisms transform it.”

01 / PLAINLY

What it means, plainly

The cycle moves nitrogen among atmosphere, soil, water, and living things through chemical transformations.

02 / CONTEXT

A little more

Microbes fix N₂ into reactive forms, while others turn ammonium into nitrate or return nitrogen to the atmosphere. Plants assimilate compounds and food webs redistribute them.

03 / WHY IT MATTERS

Why it matters

Nitrogen limits growth and connects agriculture, water pollution, atmospheric gases, and microbial communities.

04 / EXAMPLE

A familiar example

Bacteria in legume nodules fix nitrogen and receive carbon, increasing available forms within the system.

05 / LIMIT

What it does not mean

Abundant atmospheric N₂ does not mean plants and animals can incorporate it directly.

06 / NOTICE

Notice it in your day

Draw the cycle with N₂, ammonium, and nitrate; assign an organism or process to each conversion.

FINAL NOTE

The idea worth keeping

Name the chemical form and process—fixation, nitrification, assimilation, or denitrification—at each arrow.

QUESTIONS / 02

Questions people still have

Do only lightning bolts fix nitrogen?

No. Microbes perform much natural fixation, and industry also produces reactive nitrogen compounds.

Does more fertilizer always help an ecosystem?

No. Excess can pollute water, favor blooms, alter communities, and escape into the atmosphere.