---
title: "The Nitrogen Cycle and the Microbes That Drive It"
description: "Nitrogen moves between air, soil and organisms through fixation, ammonification, nitrification and denitrification, each run by particular bacteria. Unlike energy, the atoms get used again and again."
canonical: https://lightmysky.com/learn/science/the-nitrogen-cycle-and-the-microbes-that-drive-it-mt__K1J47NhWj
source: https://lightmysky.com/learn/science/the-nitrogen-cycle-and-the-microbes-that-drive-it-mt__K1J47NhWj.md
retrieved: 2026-09-12
---

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# The Nitrogen Cycle and the Microbes That Drive It

Nitrogen moves between air, soil and organisms through fixation, ammonification, nitrification and denitrification, each run by particular bacteria. Unlike energy, the atoms get used again and again.

Subject: Science · Area: Organisms & Life Processes · Ages 17 to 18
Page: https://lightmysky.com/learn/science/the-nitrogen-cycle-and-the-microbes-that-drive-it-mt__K1J47NhWj

## Ready when they can

- Names the process at each arrow of the cycle and the type of microbe that runs it.
- Contrasts a nutrient that cycles with the one-way flow of energy.
- Explains what waterlogged soil does to the balance between nitrification and denitrification.

## Lesson: The Nitrogen Roundabout

Crops need nitrogen to grow, yet plants cannot touch the nitrogen gas that fills most of the air. Fixing bacteria convert it to ammonia and ammonium, some free in soil and some in legume root nodules. Lightning fixes a little too.

Ammonifying bacteria release ammonium from dead matter and urea. Nitrifying bacteria oxidise ammonium to nitrites and then nitrates, which plants absorb best. Denitrifying bacteria reduce nitrates back to nitrogen gas, closing the loop, fastest where oxygen runs short. Unlike energy, which leaves as heat, these nitrogen atoms cycle round for reuse.

**Example.** Waterlogged fields lose their nitrates to the air. Nitrifiers need oxygen and stall in mud, while denitrifiers multiply where oxygen runs out. Draining a field flips the balance back toward nitrification.

**Tip.** Hold the big contrast ready: nitrogen compounds cycle between air, soil, and living things, while energy flows one way and leaves as heat. Name the microbe at each arrow and the pattern sticks.

**Recap.** Fixation, ammonification, and nitrification feed plants, while denitrification returns nitrogen to the air and energy only passes through.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Decomposers and the Rate of Decay](https://lightmysky.com/learn/science/decomposers-and-the-rate-of-decay-mt_4152TrzD6A)
- [Ecosystem Energy Budgets: GPP, NPP and Transfer Efficiency](https://lightmysky.com/learn/science/ecosystem-energy-budgets-gpp-npp-and-transfer-efficiency-mt_D81CKcOdBI)

## Opens up

- [Population Growth Curves and Carrying Capacity](https://lightmysky.com/learn/science/population-growth-curves-and-carrying-capacity-mt_KX6rhHF5kj)
- [Productivity, Nutrient Limitation and Ecosystem Stoichiometry](https://lightmysky.com/learn/science/productivity-nutrient-limitation-and-ecosystem-stoichiometry-mt_QWdZj1G9iT)
- [Applied Microbiology: Fermentation, Bioremediation and Host Microbiomes](https://lightmysky.com/learn/science/applied-microbiology-fermentation-bioremediation-and-host-microbiomes-mt_WcfGvV_dD9)