3.5.4 Nutrient Cycles Flashcards
General stages of phosphorus cycle
Weathering
Runoff
Assimilation
Decomposition
Uplift
Why is phosphorus cycle slow
No gas phase- no atmospheric cycle
Most stored as PO4^3- in rocks
What happens during weathering and runoff
Phosphate compounds from sedimentary rocks leach into surface water and soil
What happens during uplift
Sedimentary layers from oceans brought up land over many years
How does mining affect phosphorus cycle
Speeds up uplift
4 main stages of nitrogen cycle
Nitrogen fixation
Ammonification
Nitrification
Denitrification
Why can’t organisms use nitrogen directly from atmosphere
N2 very stable due to strong covalent triple bond
What happens during atmospheric fixation of nitrogen
High energy of lightening breaks N2 into N
N reacts with oxygen to form NO2^-
NO2^- dissolves in water to form NO3^-
Role of bacteria in nitrogen fixation
Mutualistic nitrogen fixing bacteria in nodules of legumes and free living bacteria in soil
Use enzyme nitrogenase to reduce gaseous nitrogen into ammonia
Role of bacteria in Ammonification
Saprobionts feed on and decompose organic waste containing nitrogen (urea, proteins, nucleic acids)
NH3 released
NH3 dissolves in water in soil to form NH4^+
Role of bacteria in Nitrification
2 step process carried out by saprobionts in aerobic conditions
Ammonium ions converted into NO2^- and then NO3^-
Role of bacteria in denitrification
Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen
3 benefits of planting different crop on same field each year
Nitrogen-fixing crops make soil fertile by increasing soil nitrate content
Different pathogens
Different proportions of ions used
What is organic fertiliser
Decaying organic matter and animal waste
What is inorganic fertiliser
Minerals from rocks
