NITROGEN CYCLE

1. The Nitrogen Cycle
How Nitrogen Moves Through
Ecosystems

2. Introduction to Nitrogen
• Essential element for life (proteins, DNA)
• 78% of the atmosphere is nitrogen gas (N₂)
• Not usable by most organisms in its
atmospheric form

3. Key Steps in the Nitrogen Cycle
• Nitrogen fixation
• Nitrification
• Assimilation
• Ammonification
• Denitrification

4. Nitrogen Fixation
• Conversion of N₂ into ammonia (NH₃)
• Carried out by lightning and nitrogen-fixing
bacteria (e.g., in legume roots)

5. Nitrification and Assimilation
• Nitrification: Ammonia → nitrites → nitrates
by bacteria
• Assimilation: Plants absorb nitrates; animals
get nitrogen by eating plants

6. Ammonification and Denitrification
• Ammonification: Decomposers convert
waste/dead organisms into ammonia
• Denitrification: Bacteria return nitrogen to the
atmosphere as N₂ gas

7. Human Impact
• Use of fertilizers → nitrogen runoff →
eutrophication
• Air pollution from burning fossil fuels
• Disruption of ecosystems

8. Importance of the Nitrogen Cycle
• Enables production of proteins and nucleic
acids
• Maintains ecosystem balance

9. Quiz / Recap Questions
• What organisms fix atmospheric nitrogen?
• What is the final step in the nitrogen cycle?
• Name one human impact on the nitrogen
cycle