Carbon & Nitrogen Cycles
Energy flows one-way through ecosystems, but matter cycles. Learn how carbon and nitrogen move, and who moves them.
🌿 The Carbon Cycle
Plants pull CO₂ from the atmosphere and lock carbon into glucose.
Animals & plants break glucose down → release CO₂ back to air.
Decomposers (bacteria, fungi) break down dead matter → CO₂ released.
Burning fossil fuels releases stored carbon as CO₂ — fast and a lot.
🌱 The Nitrogen Cycle
Nitrogen makes up 78% of the atmosphere as N₂ — but plants & animals can't use N₂ directly. Bacteria do almost all the work.
Bacteria (in soil & on legume roots) convert N₂ → NH₃ (ammonia).
Other bacteria convert NH₃ → NO₂⁻ → NO₃⁻ (nitrates) — the form plants absorb.
Plants take in nitrates from the soil and build proteins & DNA. Animals get N by eating plants.
Decomposers break down dead organisms & waste → release NH₃ back into soil.
Bacteria convert NO₃⁻ → N₂ gas → returns to atmosphere. Cycle closes.