The Carbon Cycle

Carbon is an essential element in all organic molecules. It forms four covalent bonds which allows it to be the backbone of all organic molecules.

Carbon Dioxide in the atmosphere is the most easily accessible abiotic reservoir
- Photosynthesis takes carbon dioxide in
- Respiration releases carbon dioxide
Carbon from dead organisms can also form reservoirs in the geosphere
Human activities can disrupt the carbon cycle by increasing the amount of carbon dioxide in the atmosphere.

The Movement of Carbon

Carbon Dioxide is the main source of carbon in the abiotic environment, but most of the accessible carbon on earth is in the biosphere - living things.

Autotrophs fix carbon dioxide from the air during photosynthesis and make organic molecules such as glucose.
- Glucose can be used for respiration, which gives off carbon dioxide back to the atmosphere.
- Glucose can also be converted to other organic molecules like starch, lipids, proteins and nucleic acids.
Heterotrophs eat food (organic molecules) and use it for respiration and making their own molecules.
When organisms die, the carbon in their bodies is released.
- Decomposers use it for their own respiration and release carbon dioxide
- Some dead organisms become part of the soil and eventually rock like limestone
- Over time, some buried carbon molecules are transformed into fossil fuels (coal, oil, natural gas)

Disruptions to the Carbon Cycle

The buildup of carbon dioxide in the atmosphere can have many negative effects on the ecosystem.

Human activities cause carbon dioxide to increase.
- Burning fossil fuels releases carbon into the atmosphere that had been stored underground for millions of years.
- Clear-cutting forests reduces the amount of autotrophs that can take carbon dioxide out of the atmosphere, and often, the trees are burned which releases even more CO2.

The increase in atmospheric CO2 can cause different kinds of damage.
- Carbon Dioxide is a greenhouse gas. It traps heat from the sun that would have otherwise escaped into space (global warming).
- It also diffuses into the water creating carbonic acid.
  - Carbonic acid can prevent crustaceans, mollusks and other marine life from making protective shells.