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Circulation of Nutrients
Environmental Biology Unit 2 Advanced Higher Biology
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Learning Objectives Describe how organic matter is decomposed by the soil fauna Understand the importance of nutrient cycling Describe the nitrogen and phosphorous cycle
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Nutrient cycling Decomposition Provides elements for
metabolic processes Constructing organic molecules Decomposition Provides mineral and nutrients for metabolism
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Soil Composition A B C D Dynamic medium Inorganic Organic
Weathering of rocks Sand, silt, clay Organic Death, decay Air and water Bedrock Topsoil Humus Leaf Litter A B C D O Increasing mineral content Increasing Organic Content
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Soil Types
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Soil Horizons
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Soil Fauna Effect the quality of soil Fungi Bacteria Invertebrates
In soil Associated with the rhizosphere Invertebrates Earthworms, woodlice, nematodes, spiders etc
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Decomposers and Detritivores
Bacteria and fungi Absorb organic nutrients from dead organisms and waste from living organisms, converting them into inorganic molecules Detritivores Organisms living in or on the soil that feed and gain nutrients from detritus.
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Litter Humus Decomposition
Breakdown of dead organic matter with release of inorganic nutrients into surrounding soil (mineralisation) Litter decomposition Humus
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Rate of decomposition Factors Type of organic matter present
Number and types of decomposers and detritivores Environmental conditions Temperature O2 content moisture
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Comparison of soils Tropical rainforest Temperate forests
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Nutrients in environment
Nutrient cycling Nutrients in environment photosynthesis decomposition decomposers producers feeding decomposition consumers
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The carbon cycle Carbon dioxide In the air (CO2) photosynthesis
respiration Combustion (burning) feeding Carbon compounds in plants Carbon compounds in animals Fossil fuels Coal, oil, gas, peat decay
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The Nitrogen Cycle
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Energy and Ecosystems Producers Consumers Decomposers Energy losses
Community Populations Habitat Ecological niche Food chains Food webs Producers Consumers Decomposers Energy losses Pyramids Number Biomass energy
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The Nitrogen Cycle Most nutrient cycles have two components
Geochemical Biological Cycling of Nitrogen Nitrogen fixation Assimilation Ammonification Nitrification denitrification
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Nitrogen Fixation Nitrogen gas converted to nitrogen- containing compounds. Three ways – all require energy Lightning nitrogen + oxygen oxides of nitrogen Industrial processes Haber process – combine hydrogen and nitrogen to form ammonia Fixation by micro-organisms
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Fixation by microorganisms
Free-living nitrogen fixers Bacteria reduce nitrogen to ammonia Used to manufacture amino acids Nitrogen rich compounds released when die and decay. Mutualistic nitrogen fixers E.g. Rhizobium Live in root nodules of leguminous plants Nitrogenase converts N2 to NH4+ using H+ and ATP Requires anaerobic conditions (leghaemoglobin) Plant uses ammonium ions to make amino acids
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Assimilation Nitrogen assimilated in the form of ammonium ions
Nitrate ions reduced to nitrite ions and then ammonium ions. Animals assimilate nitrogen in the form of protein
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Ammonification Production of ammonium-containing compounds
E.g urea, protein, nucleic acids and vitamins Decomposers feed on these releasing ammonia
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Nitrification Two stages Oxidation of ammonium ions to nitrites
Nitrosomonas Oxidation of nitrites to nitrates Nitrobacter
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Denitrification Anaerobic denitrifying bacteria
Reduce soil nitrates into nitrogen gas NO3- NO2- N2O N2
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(aerobic and anaerobic bacteria and fungi)
Nitrogen Cycle Nitrogen in atmosphere (N2) assimilation Nitrogen-fixing bacteria in root nodules of legumes Plants Denitrifying bacteria animals Nitrates (NO3-) Decomposers (aerobic and anaerobic bacteria and fungi) Nitrifying bacteria ammonification Nitrification Nitrites (NO2-) Ammonium (NH4+) Nitrifying bacteria Nitrogen-fixing soil bacteria
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Nitrogen Cycle
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The Phosphorous Cycle
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Localised phosphate cycle
Phosphate added to the soil by the weathering of rocks Producers absorb the soil phosphate Phosphorous transferred to consumers in organic form Animal excretion and decomposition returns phosphorous to the soil.
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The Phosphorous cycle Geological uplifting rain
Weathering of phosphate from rocks plants runoff Phosphate in soil Phosphate in solution animals leaching Chemical precipitation Detritus settling to bottom decomposers sedimentation
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The Phosphorous cycle
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