Biology · Class 8–10

The Nitrogen Cycle

See how nitrogen moves from the air into plants, animals and soil — and back to the air again.

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🧠 Remember it

The Nitrogen Cycle

Steps: Fixation → Nitrification → Assimilation → Ammonification → Denitrification. Air is 78% nitrogen, but plants can't use it directly — bacteria "fix" it into a usable form.

🌏 In real life

Farmers grow pulses like moong and gram because their root nodules host nitrogen-fixing bacteria that naturally enrich the soil — a free, living fertiliser.

📝 Quick notes

  • The atmosphere is about 78% nitrogen gas (N₂), but most organisms cannot use it directly.
  • Nitrogen fixation: bacteria (e.g. Rhizobium in legume roots) and lightning convert N₂ into nitrates/ammonia.
  • Nitrification: soil bacteria convert ammonia → nitrites → nitrates.
  • Assimilation: plants absorb nitrates to build proteins and DNA; animals get nitrogen by eating plants.

🎯 Test yourself

Why can't plants use nitrogen straight from the air?

Atmospheric N₂ is very unreactive; it must first be "fixed" into nitrates/ammonia by bacteria or lightning.

Learn it fully — free

See the animated, step-by-step The Nitrogen Cycle lesson on Syllab

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