Biogeochemical Cycles
What Sustains Life on Earth?
Solar energy, the cycling of matter, and gravity sustain the earth’s life.
A cycle is a series of change which comes back to the starting point and which can be repeated.
Cycling of substances is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.
The term “biogeochemical” tells us that biological, geological and chemical factors are all involved.
The circulation of chemical nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc. through the biological and physical world are known as biogeochemical cycles.
Biogeochemical Cycles describe the flow of essential elements from the environment through living organisms and back into the environment.
Hydrological Cycle (water cycle)
1. Reservoir – oceans, air (as water vapor), groundwater, lakes and glaciers; evaporation, wind and precipitation (rain) move water from oceans to land
2. Assimilation – plants absorb water from the ground, animals drink water or eat other organisms which are composed mostly of water
3. Release – plants transpire, animals breathe and expel liquid wastes
Carbon Cycle (carbon is required for building organic compounds)
1. Reservoir – atmosphere (as CO2), fossil fuels (oil, coal), durable organic materials (for example: cellulose).
2. Assimilation – plants use CO2 in photosynthesis; animals consume plants.
3. Release – plants and animals release CO2 through respiration and decomposition; CO2 is released as wood and fossil fuels are burned.
Nitrogen Cycle (Nitrogen is required for the manufacture of amino acids and nucleic acids)
1. Reservoir – atmosphere (as N2); soil (as NH4+ or ammonium, NH3 or ammonia, N02- or nitrite, N03- or nitrate
2. Assimilation – plants absorb nitrogen as either NH4+ or as N03-, animals obtain nitrogen by eating plants and other animals. The stages in the assimilation of nitrogen are as follows:
Nitrogen Fixation: N2 to NH4+ by nitrogen-fixing bacteria (prokaryotes in the soil and root nodules), N2 to N03- by lightning and UV radiation.
Nitrification: NH4+ to N02- and N02- to N03- by various nitrifying bacteria.
3. Release – Denitrifying bacteria convert N03- back to N2 (denitrification); detrivorous bacteria convert organic compounds back to NH4+ (ammonification); animals excrete NH4+ (or NH3) urea, or uric acid.
Phosphorus Cycle (Phosphorus is required for the manufacture of ATP and all nucleic acids)
1. Reservoir – erosion transfers phosphorus to water and soil; sediments and rocks that accumulate on ocean floors return to the surface as a result of uplifting by geological processes
2. Assimilation – plants absorb inorganic PO43- (phosphate) from soils; animals obtain organic phosphorus when they plants and other animals
3. Release – plants and animals release phosphorus when they decompose; animals excrete phosphorus in their waste products
Biogeochemical cycles of other minerals, such as calcium and magnesium, are similar to the phosphorus cycle.
What Sustains Life on Earth?
Solar energy, the cycling of matter, and gravity sustain the earth’s life.
A cycle is a series of change which comes back to the starting point and which can be repeated.
Cycling of substances is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.
The term “biogeochemical” tells us that biological, geological and chemical factors are all involved.
The circulation of chemical nutrients like carbon, oxygen, nitrogen, phosphorus, calcium, and water etc. through the biological and physical world are known as biogeochemical cycles.
Biogeochemical Cycles describe the flow of essential elements from the environment through living organisms and back into the environment.
Hydrological Cycle (water cycle)
1. Reservoir – oceans, air (as water vapor), groundwater, lakes and glaciers; evaporation, wind and precipitation (rain) move water from oceans to land
2. Assimilation – plants absorb water from the ground, animals drink water or eat other organisms which are composed mostly of water
3. Release – plants transpire, animals breathe and expel liquid wastes
Carbon Cycle (carbon is required for building organic compounds)
1. Reservoir – atmosphere (as CO2), fossil fuels (oil, coal), durable organic materials (for example: cellulose).
2. Assimilation – plants use CO2 in photosynthesis; animals consume plants.
3. Release – plants and animals release CO2 through respiration and decomposition; CO2 is released as wood and fossil fuels are burned.
Nitrogen Cycle (Nitrogen is required for the manufacture of amino acids and nucleic acids)
1. Reservoir – atmosphere (as N2); soil (as NH4+ or ammonium, NH3 or ammonia, N02- or nitrite, N03- or nitrate
2. Assimilation – plants absorb nitrogen as either NH4+ or as N03-, animals obtain nitrogen by eating plants and other animals. The stages in the assimilation of nitrogen are as follows:
Nitrogen Fixation: N2 to NH4+ by nitrogen-fixing bacteria (prokaryotes in the soil and root nodules), N2 to N03- by lightning and UV radiation.
Nitrification: NH4+ to N02- and N02- to N03- by various nitrifying bacteria.
3. Release – Denitrifying bacteria convert N03- back to N2 (denitrification); detrivorous bacteria convert organic compounds back to NH4+ (ammonification); animals excrete NH4+ (or NH3) urea, or uric acid.
Phosphorus Cycle (Phosphorus is required for the manufacture of ATP and all nucleic acids)
1. Reservoir – erosion transfers phosphorus to water and soil; sediments and rocks that accumulate on ocean floors return to the surface as a result of uplifting by geological processes
2. Assimilation – plants absorb inorganic PO43- (phosphate) from soils; animals obtain organic phosphorus when they plants and other animals
3. Release – plants and animals release phosphorus when they decompose; animals excrete phosphorus in their waste products
Biogeochemical cycles of other minerals, such as calcium and magnesium, are similar to the phosphorus cycle.
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