The Nitrogen Cycle — Interactive Diagram

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

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

Why it matters: Nitrogen is essential for proteins and DNA. Fixation, nitrification and denitrification are commonly tested in biology and environmental science.

The Nitrogen Cycle — Step by Step

1. FIXATION: nitrogen gas (N₂) makes up 78% of air but plants can’t use it directly. Bacteria in roots and lightning fix it into usable nitrates.
2. Plants ABSORB nitrates from the soil to build proteins. Animals get nitrogen by eating the plants.
3. DECOMPOSITION & DENITRIFICATION: when plants and animals die, decomposers return nitrogen to the soil, and some bacteria release N₂ back to the air. The cycle continues!

Quick Notes — the Exam Crux

• 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.
• Ammonification: decomposers turn dead matter and waste back into ammonia.
• Denitrification: bacteria convert nitrates back to N₂ gas, returning it to the air.

Remember It (Memory Trick)

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

Real-Life Example

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

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.

Which bacteria fix nitrogen in the roots of leguminous plants?

Rhizobium bacteria, living in the root nodules.

What does denitrification do?

Converts nitrates in the soil back into nitrogen gas, releasing it to the atmosphere.

📖 Read the full explanation of The Nitrogen Cycle →

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