The carbon cycle in the biosphere is a complex process involving the continuous exchange of carbon among the atmosphere, oceans, land, and living organisms.
Here's a breakdown of the process:
1. Carbon Fixation (Photosynthesis):
Plants, algae, and some bacteria (primary producers) absorb carbon dioxide (CO2) from the atmosphere during photosynthesis. They use sunlight, water, and CO2 to create sugars (carbohydrates) and other organic compounds. This process converts inorganic carbon (CO2) into organic carbon within the biosphere.
- Equation: 6CO2 + 6H2O + Sunlight → C6H12O6 + 6O2 (Carbon dioxide + Water + Sunlight → Glucose + Oxygen)
2. Consumption and Transfer:
Animals (consumers) obtain carbon by eating plants or other animals. As they consume organic matter, they break it down through cellular respiration to obtain energy. This process releases some carbon back into the atmosphere as CO2. Carbon is thus transferred through the food web.
3. Respiration:
Both plants and animals perform cellular respiration, breaking down organic compounds to release energy. A byproduct of this process is CO2, which is released back into the atmosphere.
4. Decomposition:
When plants and animals die, their bodies decompose. Decomposers, such as bacteria and fungi, break down the organic matter in dead organisms and waste products. This process releases carbon back into the atmosphere as CO2. In some environments, decomposition occurs slowly (e.g., in peat bogs or permafrost), leading to the accumulation of carbon in the soil.
5. Storage:
Carbon can be stored in various reservoirs within the biosphere:
- Living Biomass: Trees, plants, and animals store carbon in their tissues. Forests are particularly important carbon sinks.
- Soil: Soil contains a large amount of organic carbon from decaying plant and animal matter. Permafrost regions store vast amounts of carbon in frozen organic material.
- Oceans: The ocean absorbs CO2 from the atmosphere. This carbon can be stored in dissolved form, used by marine organisms, or deposited as sediment on the ocean floor. Carbon can also exist as dissolved inorganic carbon (DIC), particulate organic carbon (POC), and dissolved organic carbon (DOC).
6. Release:
Carbon is released back into the atmosphere through:
- Respiration: As mentioned above, plants, animals, and decomposers release CO2 during respiration.
- Decomposition: Decomposition of organic matter releases CO2.
- Combustion: Burning of fossil fuels (coal, oil, natural gas) and biomass releases large amounts of CO2 into the atmosphere. This is a significant factor contributing to climate change.
- Volcanic Eruptions: Volcanoes release CO2 from the Earth's interior.
- Deforestation: Clearing forests reduces the amount of carbon stored in biomass and can lead to increased decomposition of soil organic matter.
The Carbon Cycle in a Table:
| Process | Description | Carbon Form | Reservoir |
|---|---|---|---|
| Photosynthesis | Plants absorb CO2 from the atmosphere to create organic compounds. | CO2 → Organic Carbon (e.g., Glucose) | Atmosphere → Plants |
| Consumption | Animals eat plants or other animals to obtain carbon. | Organic Carbon | Plants/Animals → Animals |
| Respiration | Plants and animals break down organic compounds, releasing CO2. | Organic Carbon → CO2 | Plants/Animals → Atmosphere |
| Decomposition | Decomposers break down dead organisms and waste, releasing CO2. | Organic Carbon → CO2 | Dead Organisms/Waste → Atmosphere/Soil |
| Storage | Carbon is stored in living organisms, soil, oceans, and sediments. | Organic Carbon, CO2, DIC, POC, DOC | Biomass, Soil, Oceans, Sediments |
| Combustion | Burning of fossil fuels and biomass releases CO2. | Organic Carbon → CO2 | Fossil Fuels/Biomass → Atmosphere |
| Ocean Absorption | Oceans absorb CO2 from the atmosphere. | CO2 | Atmosphere → Oceans |
The balance of these processes determines the amount of carbon stored in different reservoirs and the overall concentration of CO2 in the atmosphere. Human activities, particularly the burning of fossil fuels and deforestation, have significantly altered the carbon cycle, leading to increased atmospheric CO2 levels and climate change.
