The Carbon Cycle
Carbon is one of the most important elements of life, forming the backbone of all organic molecules. The main source of carbon is carbon dioxide (CO₂) present in the atmosphere. CO₂ is also highly soluble in water, so oceans hold significant dissolved carbon.
Steps in the Global Carbon Cycle
1. Photosynthesis
- Green plants absorb atmospheric CO₂ in the presence of sunlight and convert it into organic food through photosynthesis.
- Oxygen is released as a by-product.
- Part of the food produced is used by the plant for its own metabolism, while the rest is stored as biomass, which becomes available to herbivores, heterotrophs, and decomposers.
- Annually, about 4–9 × 10¹³ kg of CO₂ is fixed by plants globally.
- Forests act as carbon reservoirs, storing carbon in their long-lived biomass. However, forest fires can release large amounts of CO₂ back into the atmosphere.
2. Respiration
- Respiration is carried out by all living organisms. It is a metabolic process where food is oxidized to liberate energy, CO2 and water. The energy released from respiration is used for carrying out life processes by living organism (plants, animals, decomposers etc.). Thus CO2 is released into of the atmosphere through this process.
3. Decomposition
- All the food assimilated by animals or synthesized by plant is not metabolized by them completely. A major part is retained by them as their own biomass which becomes available to decomposers on their death. The dead organic matter is decomposed by microorganisms and CO2 is released into the atmosphere by decomposers.
4. Combustion
- Burning of biomass (e.g., wood, crop residue) and fossil fuels releases stored carbon as CO₂.
5. Human Activities
- Since the industrial era, human activities have significantly disturbed the carbon cycle.
- Large-scale deforestation and increasing consumption of fossil fuels by industries, vehicles, and power plants have caused a marked rise in atmospheric CO₂.
- The continuous rise in CO₂ concentration is a major cause of global warming and climate change.
