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Biogeochemical Cycles Where do macromolecules come from & Where do they go? Elements transferred between compartments (pools) Active: accessible to living things Storage: inaccessible Biogeochemical Cycle Overview What is a Biogeochemical Cycle? • Reuse of materials in ecosystem by living organisms • Biological components (biotic): – Producers – Consumers – Detritivores (scavengers & decomposers) • Geological components (abiotic): – Atmosphere (gases & water vapor) – Solid crust of the earth (minerals & chemicals) – Earth’s water (oceans, lakes & rivers) Biogeochemical Cycles • Water – needed to make CARBOHYDRATES, LIPIDS, PROTEINS THE WATER CYCLE Other Biogeochemical Cycles • Water cycle • Carbon – needed to make CARBOHYDRATES, LIPIDS, PROTEINS, & NUCLEIC ACIDS CARBON CYCLE atmosphere respiration photosynthesis biosphere CARBON CYCLE CARBON CYCLE combustion photosynthesis respiration atmosphere biosphere Other Biogeochemical Cycles • Water cycle • Carbon cycle • Nitrogen – needed to make PROTEIN & NUCLEIC ACIDS gain fixation loss atmosphere biosphere denitrification Nitrogen Cycle Nitrogen Cycle • Despite abundance in the atmosphere (77% of Earth’s atmosphere made of N2 gas) nitrogen is actually a limiting factor to plant growth • Most organisms cannot use elemental N2 and must use nitrogen present in soil minerals • N2 gas is “fixed” into these nitrogen compounds mainly by bacterial processes Stages of Nitrogen Cycle • Ammonification – Most soil nitrogen is result of decomposition of nitrogenous compounds by bacteria (amino acids, proteins, etc.) – These bacteria release excess nitrogen in the form of ammonia (NH3) or ammonium ions (NH4+) Stages of Nitrogen Cycle • Ammonification • Nitrification (by nitrogen-fixing bacteria) – Several species of bacteria able to oxidize ammonia to get energy for metabolism: 2NH3 + 3O2 2NO2- + 2H+ + 2H2O – Although nitrite (NO2-) is toxic, it is quickly changed to nitrate (NO3-) by another group of bacteria: 2NO2- + O2 2NO3- NITRATE – Most plants take up nitrogen in the form of nitrate Stages of Nitrogen Cycle • Ammonification • Nitrification • Assimilation – Requires energy expenditure to attach ammonium ions to carbon-containing compounds – Amino acids produced: Amino acids form PROTEINS Loss of Soil Nitrogen • Nitrates steadily lost from cycle by: – Harvesting plants – Soil erosion – Fire – Leaching – Denitrifying bacteria – these break down nitrate into N2 gas (in the absence of oxygen); usually takes place in poorly drained soil NITROGEN CYCLE ANIMATION Other Biogeochemical Cycles • • • • Water cycle Carbon cycle Nitrogen cycle Phosphorus – needed to make DNA & RNA (nucleic acids) as well as ATP (the energy currency of cells) PHOSPHORUS CYCLE Other Biogeochemical Cycles • • • • Water cycle Carbon cycle Phosphorus Sulfur – needed to make certain proteins SULFUR CYCLE Questions: What would happen if a biogeochemical cycle “slowed down” or “sped up?” What might cause such a thing to happen? Turn to your neighbor and explain. Then write a summary of what you both concluded.