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.
What a learner can do afterwards
- 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.
1 · Read
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.
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.
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.
Fixation, ammonification, and nitrification feed plants, while denitrification returns nitrogen to the air and energy only passes through.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.