Bio 130 Nitrogen cycle
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Why is nitrogen essential for life?. It is a key component of amino acids
proteins
What percentage of Earth’s atmosphere is nitrogen gas (N₂)?
~78%
Why can’t most organisms use atmospheric N₂ directly?
The triple bond in N₂ is very strong and requires a lot of energy to break
Which organisms can convert atmospheric N₂ into usable forms?
Certain prokaryotes (bacteria)
What is bioavailable nitrogen?
Nitrogen in chemical forms organisms can use (NH₄⁺ or NO₃⁻)
Why is nitrogen often a limiting nutrient?
Most nitrogen is locked in atmospheric N₂
How does nitrogen availability affect ecosystems?
It controls productivity
What are the five major processes in the nitrogen cycle?.
Nitrogen fixation
Which nitrogen cycle process does NOT require bacteria?
Assimilation
What is nitrogen fixation?
Conversion of N₂ gas into ammonia (NH₃) or nitrate (NO₃⁻)
What are the three types of nitrogen fixation?
Lightning
How does lightning fix nitrogen?
Energy breaks N₂ bonds
What is biological nitrogen fixation (BNF)?
Nitrogen fixation carried out by bacteria using the enzyme nitrogenase
What is nitrogenase?
An enzyme that breaks the N₂ triple bond
What bacteria live in legume root nodules?.
Rhizobia
What do plants provide rhizobia in symbiosis?
Sugars from photosynthesis
What do rhizobia provide plants?.
Ammonium (NH₄⁺)
What is the Haber process?
Industrial nitrogen fixation producing ammonia using heat
What is assimilation?.
Uptake of NH₄⁺ or NO₃⁻ by plants and incorporation into organic molecules
How do animals assimilate nitrogen?
By eating plants or other animals
What is ammonification?
Conversion of organic nitrogen into ammonium (NH₄⁺)
What organisms carry out ammonification?
Decomposer bacteria and fungi
What is nitrification?
Conversion of NH₄⁺ to NO₃⁻
What organisms carry out nitrification?
Nitrifying bacteria
Why is nitrification important for plants?
Most plants prefer nitrate (NO₃⁻)
What is denitrification?
Conversion of NO₃⁻ into N₂ gas
What organisms perform denitrification?
Anaerobic bacteria
Why can denitrification reduce ecosystem productivity?
It removes bioavailable nitrogen from the system
What greenhouse gas can be released during denitrification?
Nitrous oxide (N₂O)
How have humans changed the nitrogen cycle?
Doubled nitrogen fixation through fertilizers
Why was increased nitrogen fixation beneficial?
It increased crop productivity and food supply
Why is excess nitrogen harmful?
The nitrogen cycle is “leaky
How does nitrogen contribute to air pollution?
NOx emissions from fossil fuels cause smog and acid rain
What is acid rain made of in the nitrogen cycle?
Dilute nitric acid
Why is nitrous oxide (N₂O) dangerous?
It is a greenhouse gas and destroys ozone
How does nitrate leaching affect soils?
It removes important cations (Ca²⁺
Why does nitrate leach easily?
Soil particles do not hold negatively charged nitrate well
How does ammonium fertilizer increase soil acidity?
It increases nitrification rates
What is eutrophication?
Excess nutrients cause excessive plant growth in water
What happens after eutrophication?
Decomposition depletes oxygen
What is hypoxia?
Low oxygen conditions that kill aquatic organisms
What major ecosystem has a nitrogen-driven dead zone?
The Gulf of Mexico
What is methemoglobinemia (“blue baby syndrome”)?
Nitrate contamination prevents oxygen transport in infants
What is nitrogen saturation?
When ecosystems receive more nitrogen than they can retain
How does nitrogen saturation affect biodiversity?
Species adapted to low nitrogen are outcompeted
What happens to nitrogen in Sewanee’s wastewater?
It is converted back to atmospheric N₂
What nitrogen cycle processes occur at SUD?
Ammonification
Why are algae important in the lagoons?
They assimilate nitrate and provide carbon for denitrifiers
What happens to nitrate after 40 days in lagoons?
It drops below detectable limits
What happens to treated wastewater in Sewanee?
It is sprayed onto forest land
What is a constructed wetland?
A human-designed system that mimics natural wetlands for water treatment
What do constructed wetlands remove?
Nutrients (N
What are PPCPs?
Pharmaceuticals and personal care products
Why are PPCPs concerning?
They affect aquatic organisms and are not EPA-regulated
What role do bacteria play in the nitrogen cycle?
They mediate nearly all nitrogen transformations
Why is the nitrogen cycle closely linked to human health?
It affects air quality