AP Environmental Science · Unit 1 The Living World
Learning Objectives
Fixation: Bacteria convert inert N₂ gas into Ammonia (NH₃/NH₄⁺).
Nitrification: Soil bacteria convert Ammonia into Nitrites (NO₂⁻) then Nitrates (NO₃⁻).
Assimilation: Plants absorb NO₃⁻ or NH₄⁺ through roots to build proteins/DNA.
Denitrification: Bacteria in anaerobic conditions convert NO₃⁻ back to N₂ gas.
Tags
NitrogenBacteriaMacromoleculesAgriculture
The 5 Steps of the Cycle (FNAAD)
Nitrogen Fixation
N₂ gas from the atmosphere is biologically "fixed" by Rhizobium bacteria living in the root nodules of legumes (or lightning). It is converted into Ammonia (NH₃), which quickly reacts with water to form Ammonium (NH₄⁺).
N₂ → NH₃ / NH₄⁺
Human Impact (Haber-Bosch)
Humans artificially fix N₂ into synthetic fertilizers. Excess fertilizer run-off causes Eutrophication in water bodies (algal blooms, dead zones).