Download Chemistry of the Cycles

Chemistry of the Cycles
Sulfur Cycle
• Sulfur is one of the constituents of many proteins, vitamins,
and hormones. It recycles like other biogeochemical cycles
• The essential steps of the sulfur cycle are:
• Mineralization of organic sulfur to the inorganic form, hydrogen
sulfide: (H2S).
• Oxidation of sulfide (s2-) and elemental sulfur (S) and related
compounds to sulfate, (SO42-).
• Conversion of sulfate (SO42-) to sulfide (s2-).
• Microbial immobilization of the sulfur compounds and subsequent
incorporation into the organic form of sulfur
Sulfur Cycle
• The Chemistry:
• Sulfate (SO42-) is reduced to organic sulfhydryl groups (R-SH) by
plants, fungi, and various prokaryotes.
• Organic molecules containing sulfur can be desulfurated, producing
hydrogen sulfide gas (H2S)
• Hydrogen sulfide, (H2S) is broken down producing elemental sulfur
(So), This reaction is done by the photosynthetic green and purple
sulfur bacteria and some chemolithotrophs (organisms using inorganic
compounds for ATP production).
• Further oxidation of elemental sulfur by sulfur oxidizers produces
sulfate, (SO42-)
• Elemental sulfur can be converted to hydrogen sulfide, (H2S)
• Sulfate reducers generate hydrogen sulfide, (H2S) from sulfate, (SO42-)
Phosphorus Cycle
•
The phosphorus cycle process is as follows:
• The phosphorus enters the soil and water as phosphate ions , (PO4)3- through the
weathering of rocks.
• Plants take in these phosphate ions from the soil.
• The phosphates, (PO4)3- are then transferred from plants to herbivores animals.
• These herbivores animals are eaten by carnivores.
• The phosphates that are absorbed by the animals are returned to the soil through
excretion and from decomposition of plants and dead material by microbes.
• The dead plant materials and other waste products are decayed through the action of
bacteria.
• The phosphate is released out to the environment by this process.
• The phosphate in the soil is leached out or eroded into water.
• The water is again utilized by algae and plants as nutrients.
Phosphorus cycle
• The phosphorus cycle differs from the other major
biogeochemical cycles in that it does not include a gas phase;
although small amounts of phosphoric acid (H3PO4) may
make their way into the atmosphere, contributing—in some
cases—to acid rain.
Nitrogen Cycle
• Fixation by Lightning
The energy from lightning causes nitrogen (N2) and water (H2O)
to combine to form ammonia (NH3) and nitrates (NO3).
Precipitation carries the ammonia and nitrates to the ground,
where they can be assimilated by plants.
• Biological Fixation
About 90% of nitrogen fixation is done by bacteria. Cyanobacteria
convert nitrogen into ammonia and ammonium.
N2 + 3 H2 → 2 NH3
• Ammonia (NH3) can be used by plants directly. Ammonia and
ammonium may be further reacted in the nitrification process.
Nitrification
• Nitrification occurs by the following reactions:
• 2 NH3 + 3 O2 → 2 NO2 + 2 H+ + 2 H2O
2 NO2- + O2 → 2 NO3-
• Aerobic bacteria use oxygen to convert ammonia (NH3) and
ammonium (NH4)1+
• Nitrosomonas bacteria convert nitrogen (N2) into nitrite (NO2-)
and then nitrobacteria convert nitrite (NO2-) to nitrate (NO3-).
• Some bacteria exist in a symbiotic relationship with plants
(legumes and some root-nodule species). Plants utilize the nitrate
as a nutrient. Animals obtain nitrogen by eating plants or planteating animals.
Ammonification
• When plants and animals die, bacteria convert nitrogen
nutrients back into ammonium salts and ammonia. This
conversion process is called ammonification. Anaerobic
bacteria can convert ammonia into nitrogen gas through the
process of denitrification:
• NO3- + CH2O + H+ → ½ N2O + CO2 + 1½ H2O
• Denitrification returns nitrogen to the atmosphere,
completing the cycle.
Nitrogen Cycle
Carbon Cycle
• Key Concepts
• Carbon is constantly being used and reused by living things
• The original energy source is the sun
• Chlorophyll is green plants absorbs energy from the sun and converts
it to chemical energy through photosynthesis
• Photosynthesis converts atmospheric CO2 into glucose, C6H12O6
• In the cells of living things energy is released during respiration
• Respiration converts glucose C6H12O6 into CO2
• Carbonates CO32- is leached out of sedimentary rocks into ground and
groundwater then converted into CO2
Chemistry of Carbon Cycle
•
Photosynthesis:
•
6CO2 + 6 H2O  C6H12O6 + 6O2
•
Animals eat plants or other animals that have eaten plants and incorporate the C atoms
into their cells.
•
Plant and animals respire converting glucose into CO2
•
C6H12O6 + 6 O2  CO2 + 6H2O
•
During decomposition carbon containing molecules are converted into elemental C
•
Carbonate ion contained in sedimentary rock is leached out and converted to CO2 by the
following process:
Chemistry of Carbon Cycle
• Humans burn fossil fuels converting elemental C into CO2
• C + O2  CO2
• CH4 + O2  CO2 + 2H2O