1. Carbon Cycling
4.3

2. Carbon Fixation
Autotrophs are responsible for taking CO2 out of the atmosphere and converting it into carbohydrates.
Keeps atmospheric concentration steady.

3. CO2 in Solution Soluble in water.
Can be dissolved gas or as carbonic acid(H2CO3).
Can be absorbed by plants.

4. Absorption of CO2
Autotrophs use CO2 to make C compounds, reducing concentration inside.
Creates a concentration gradient, allowing CO2 to diffuse in from atmosphere.

5. Release of CO2 CO2 is waste product of cellular respiration.
Diffuses out of the cells into atmosphere or water.

6. Methanogenesis Production of methane gas by anaerobic bacteria.
Bacteria that make methane are methanogenic and exist in various anaerobic environments.
Some methane is released into the atmosphere, some is kept by organisms and used for food.

7. Oxidation of Methane
Methane is naturally oxidized in the atmosphere by monatomic O and highly reactive hydroxyl radicals (OH·)

8. Peat
Happens in anaerobic environment when organic matter is not fully decomposed.
Water logged soils prevent air from permeating, creating acidic conditions.

9. Fossilized Organic Matter
If peat is heated and pressed, it can form coal.
At the bottom of bodies of water, mud can create anaerobic conditions.
As more mud and sediments deposit, the liquid material can form crude oil.

10. Combustion
CO2 is released into the atmosphere by burning of biomass (living tissues) in presence of O2.
Can naturally occur, but most combustion occurs due to human activities.

11. Limestone Some animals use CaCO3 to make body parts or build reefs.
In right situations, CaCO3 can be stored as limestone.