2. BIOGEOCHEMICAL CYCLES
Sun- continuous stream of energy
Most common elements in living organisms are C, N, O, P & S
Microorganisms interact with each other,transfer nutrients
Nutrient cycling-exchange of C,N,S,Fe & Mn
Biogeochemical involves both biological & chemical processes
Nutrients are transferred and exchanged ,by oxidation-
reduction reactions
All biogeochemical cycles are linked
5. *
*Inorganic C-containing molecules organic molecules
used by orgnsms release of inorganic C molecules back
to atmosphere
*Reduced forms-CH4 and organic matter
*Oxidized forms-CO,CO2
*Producers – photosynthetic production of carbohydrates and O2
using CO2 and H2O
*Half the C on earth is fixed by cyanobacteria,prochlorococcus
and synechococcus, and diatoms
*Also fixed by chemolithoautotrophic microbes
6. *Consumers-C containing molecules are incorporated into
body,respiration,release of CO2 and H2O
*Inorganic[CO2] and organic C reduced to CH4 anaerobically,CH4 is
produced by archaea in anoxic habitats
*Decomposers-organic molecules are used as food, it's respiration
release CO2 and H2O
*Most C substrates can be degraded easily with or without O2 except
hydrocarbons and lignin
*Oxic condition-oxidized products such as nitrate, sulfate and CO2
*Anoxic-reduced end products such as ammonium ion ,sulfide and
CH4
8. *Cycling of N atoms between abiotic and biotic components and
among organisms
*N is essential in formation of proteins and nucleic acids
*N2 ~ 80% of earth’s atmosphere
*N atoms are tightly bound, plants and producers must get it as
nitrate(NO3-) or ammonia(NH3)
*N fixation is uniquely prokaryotic process; apart fixation during
lightning
*Nitrogen fixing bacteria-covert N2 into NH3
• Free-living N2-fixing bacteria
• Symbiotic N2-fixing bacteria
9. *Microbes such as Azotobacter and the cyanobacterium
Trichodesmium fix nitrogen aerobically,free-living
anaerobes Clostridium fix anaerobically
*Symbiotic N fixing- Rhizobium, α-proteobacteria and β-
proteobacteria
*Product of N2 fixation ammonia(NH3),incorporated into
organic matter as an amine
10. *Producers and consumers-plants,synthesis of proteins and
nucleic acid.Herbivores & carnivores-breakdown proteins
& nucleicacids to smaller blocks
*Decomposers
• Ammonia is released
• Nitrifying bacteria-convert ammonia to nitrite,which can be
converted by other bacteria to nitrate
• Plants use ammonia & nitrate
• Denitrifying bacteria-anaerobic conversion of nitrate to
nitrogen gas
11. *Ammonia nitrate ,called nitrification, 2 step process-
ammonium nitrite nitrate
*Nitrosomonas and Nitrosococcus in the 1st step ,Nitrobacter
and related bacteria in the 2nd step
*Nitrate can be reduced & incorporated into organic
compounds, assimilatory nitrate reduction
*Some microbes(eg,Pseudomonas denitrificans)-dissimilatory
reduction, nitrate N2 gas, denitrification
*Anammox reaction-chemolithotrophs use ammonium ion and
nitrite,which is reduced to N2 gas
12. PHOSPHORUS CYCLE
• Phosphorus – nucleic acid & cell membrane ,bones & teeth
• P cycle has no gaseous component
• Most of the processes are geological processes of erosion &
deposition
• P is present in low concentrations, locked in Earth’s crust
• P is solely derived from weathering of P-containing rocks
• Released by erosion of rock & are dissolved in water
• In soil- inorganic & organic forms
13.
14. *Organic phosphorus-biomass & humus, recycled by microbial
activity
*Inorganic phosphorus- negatively charged, complexes with
cations such as iron,aluminium, and calcium
*These compounds are relatively insoluble, dissolution is pH
dependent- available to plants & microbes between pH 6 and
7
*These organisms rapidly convert phosphate organic
form available to animals
*Animals obtain P when they consume plants & animals
*Organism dies, excretes P back to soil
*P compounds that are dissolved in water get precipitated as
mineral deposits in oceans
decomposers
16. *Much of the Earth’s sulfur is stored underground in rocks and
minerals, including sulfate salts buried deep under ocean sediments
*Sulfur enters the atmosphere from several natural sources
*H2S is released from active volcanoes & from organic matter
*S02 also comes from volcanoes
*Particles of sulfate (SO4 2-) salts enter the atmosphere from sea
spray and dust storms
*Sulfide elemental sulfur and sulfate
17. *Plant roots absorb sulfate ions & incorporate the S as an essential
component of many proteins
*When sulfate diffuses into reduced habitats,it provides an
opportunity for different groups of microorganisms (eg
Desulfovibrio) to carry out sulfate reduction
• Dissimilatory sulfate reduction results in sulfide accumulation in the
environment
• Assimilatory sulfate reductiion- the reduction of sulfate for use in
aminoacid & protein biosynthesis
*Sulfate an be reduced to sulfide by a wide variety of
microorganisms ,including Alteromonas & Clostridium
18. *Certain marine algae produce large amounts of volatile
dimethyl sulfide(DMS)
*Human activities –large amounts of sulfur dioxide into
atmosphere
*Once in atmosphere ,SO2 is converted to droplets of
sulfuric acid & particles of sulfate ,which return to the Earth
as acid deposition
20. *Oxygen cycle is the biogeochemical cycle of oxygen within
its three main reservoirs-
1. atmosphere(air)
2. total content of biological matter within the biosphere
3. Earth’s crust
21. The steps involved in the oxygen cycle are;
1.Photosynthesis-
During the day, plants take energy from the Sun ,CO2 from the
air, and H2O from the soil to make their food-glucose.O2 is
released into air as a by-product
During the night, plants take in O2 and releaseCO2,to maintain
their metabolism
2.Respiration –
O2 released by plants is used by humans ,animals ,and other
organisms for respiration and release CO2 into the air
24. Note: The complementary processes of
photosynthesis and respiration ensure that not
only oxygen, but also carbon and hydrogen
are repeatedly cycled.
Photosynthesis:
6 CO2 + 6 H2O + light ------> C6H12O6 + 6O2
Respiration:
C6H12O6 + 6O2 ------> 6CO2 + 6H2O + energy