5.4 Nutrient Cycles Flashcards
Name the 5 stages of the phosphorus cycle.
Weathering
Runoff
Assimilation
Decomposition
Uplift
Why is the phosphorus cycle slow?
Stored as PO₄³⁻
Phosphorus has no gas phase so no atmospheric cycle
What happens during weathering and runoff?
Phosphate compounds from sedimentary rocks leach into surface water and soil
Explain the significance of phosphorus to living organisms.
Converted from inorganic phosphate into biological molecules e.g. DNA, ATP, NADP
What happens during uplift?
Sedimentary layers from oceans formed by bodies of aquatic organisms are brought up to land over many years
How does mining affect the phosphorus cycle?
Speeds up uplift
Name the 4 main stages of the nitrogen cycle.
Nitrogen fixation
Ammonification
Nitrification
Denitrification
Why can’t organisms use nitrogen directly from the atmosphere?
N₂ is very stable due to strong covalent triple bond
What happens during atmospheric fixation of nitrogen?
High energy of lightning breaks N₂ into N
N reacts with oxygen to form NO₂⁻
NO₂⁻ dissolves in water to form NO₃⁻
Outline the role of bacteria in nitrogen fixation.
Nitrogen-fixing bacteria in nodules of legumes & free-living bacteria in soil
Use enzyme nitrogenase to reduce gaseous nitrogen into ammonia
Outline the role of bacteria in ammonification.
Saprobionts feed on and decompose organic waste containing nitrogen (e.g. urea, proteins, nucleic acids etc)
NH₃ released
NH₃ dissolves in water in soil to form NH₄⁺
Outline the role of bacteria in nitrification.
2-step process carried out by saprobionts in aerobic conditions:
2NH₄⁺ + 3O₂ -> 2NO₂⁻ + H₂O + 4H⁺
2NO₂⁻ + O₂ -> 2NO₃⁻
What are saprobionts?
Decomposers that digest their material externally by secreting enzymes onto dead organisms and waste material
Outline the role of bacteria in denitrification.
Anaerobic denitrifying bacteria convert soil nitrates back into gaseous nitrogen
Explain the significance of nitrogen to living organisms.
Plant roots uptake nitrates via active transport & use them to make biological compounds e.g. amino acids, NAD/NADP, nucleic acids