Lesson 5 ·Class 9 · Economic Importance of Bacteria and Fungi · Flow Lab
Bacteria and the Nitrogen Cycle
Air is 78% nitrogen — and plants cannot use any of it.
Nitrogen gas is useless to a plant until bacteria change it. Follow one atom around the cycle.
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💨 Step 1 of 6 · Nitrogen in the air
Nitrogen gas makes up most of the air, but its triple bond makes it inert — plants cannot absorb it.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Fixation makes nitrogen available; denitrification sends it back to the air. Bacteria run both ends.
What this lesson covers
Challenges to clear
- Advance to the step that makes nitrogen usable in the first place.
- Reach the step that produces the nitrates roots absorb.
- Go all the way round the cycle.
The task
Nitrogen gas is useless to a plant until bacteria change it. Follow one atom around the cycle.
What this lesson covers
- Nitrogen in the air — Nitrogen gas makes up most of the air, but its triple bond makes it inert — plants cannot absorb it.
- Nitrogen fixation — Rhizobium in root nodules and free-living Azotobacter convert nitrogen gas into ammonia.
- Nitrification — Nitrosomonas turns ammonia into nitrites; Nitrobacter turns nitrites into nitrates — the form roots absorb.
- Plants take up nitrates — Roots absorb nitrates and build them into amino acids and proteins. Animals get their nitrogen by eating plants.
- Ammonification — When organisms die or excrete, decomposing bacteria break the proteins back down to ammonia.
- Denitrification — Pseudomonas and other denitrifying bacteria return nitrates to nitrogen gas, closing the cycle.
Hint
Fixation makes nitrogen available; denitrification sends it back to the air. Bacteria run both ends.