Carbon Cycle

Nitrogen Cycle

Sulfur Cycle

Basic ecology
primary producers are autotrophs that convert inorganic carbon (CO₂) into organic carbon (sugars, amino acids, etc.)
This conversion requires energy
Different autotrophs use different energy sources
Photosynthetic organisms use the energy in sunlight
other microbes using the reducing power of H₂
other microbes use minerals - eg., converting Fe_reduced to Fe_oxidized
primary consumers eat autotrophs
these organisms are herbivores, like cows
secondary consumers eat the primary consumers
these organisms are flesh-eaters, like man
Man eats cows and cows eat plants and plants make food with sunlight
Analogously, Nematodes eat protozoa and protozoa eat algae and algae make food with sunlight
Decomposers break is all back down to simpler molecules

Carbon chemistry
carbon has four bonds
Important carbon molecules - CO₂ (carbon dioxide), CH₄ (methane), HCO₃^- (bicarbonate), CaCO₃ (calcium carbonate), CH₂O (carbohydrate)
Carbon dioxide and methane are gases (atmospheric)
Bicarbonate is found in waters (oceanic)
Calcium carbonate is found in rocks (terrestrial)
Carbohydrates and like molecules are organics and found in living things

Redox chemistry is the key to global carbon cycles
adding oxygens is oxidation
adding hydrogens (electrons) is reduction
CH₄ to CO₂ is an oxidation
CO₂ to CH₄ is a reduction
CO₂ to CH₂O is a reduction (photosynthesis)
CH₂O to CO₂ is an oxidation (respiration)

The Carbon Cycle
Showed how each of these reactions fits into the scheme
Emphasized how Redox chemistry is the key process
discussed aerobic versus anaerobic arms of the cycle

Global carbon cycles and global warming
Burning fossil fuels is and oxidation
Fossils fuels locked in Earth for eons now suddenly oxidized
Causes excess CO₂ in atmosphere
Beyond the ability of the oceans to buffer
Carbon dioxide is a greenhouse gas since it causes heat energy to be retained in the atmosphere
This leads to global warming
This may eventually melt the ice caps and change the types of organisms that are successful and which predominate on Earth

Nitrogen Chemistry
Analogous to carbon chemistry - Redox reactions
nitrogen has 3 bonds
important nitrogen compounds - N₂ (dinitrogen), NH₃, NO₂^-1 (nitrite), NO₃^-3 (nitrate), N₂O (nitrous oxide; laughing gas)
N₂ to NH₃ is a reduction
NH₃ to NO₂^-1 to NO₃^-3 to N₂ are oxidations
Each of these oxidations provide energy (a slow burn)
Certain microbes make their entire living from just one of these reactions
N₂ to NH₃ is called nitrogen fixation
this is a very expensive reaction

The Nitrogen cycle
Point out the different reactions in the cycle
discuss aerobic vs. anaerobic arms of the cycle
Point out the interdependence of organisms
Nitrosofying bacteria convert ammonia to nitrite
Nitrifying bacteria convert that nitrite to nitrate
the nitrifying bacteria could not live without the nitrosofying bacteria
one bacteria eating another bacteria's waste product

Synthetic ammonia production
Haber process produces ammonia for agricultural fertilizer
Too much fixed nitrogen entering the environment is upsetting the normal balance of nitrogen and carbon cycles
excess ammonia applied to fields runs off with the rain into lakes and streams
this fixed nitrogen encourages algal grow which is naturally nitrogen limited
the algae produce a lot of biomass which is then eaten by heterotrophic bacteria
these bacteria respire and use up the available oxygen
the lake becomes essentially anaerobic
the fish die, the lake smells
the environment is degraded

Sulfur cycles
the sulfur cycle is mentioned just to show that it also runs on redox chemistry
H₂S to S⁰ to SO₄ are oxidations (a slow burn>
SO₄ is then reduced back to H₂S completing the cycle
different microbes make a living off just one of these reactions