Biogeochemical Cycles (Nutrient Cycles) - The Carbon Cycle

The carbon cycle is the continuous circulation and recycling of carbon between the atmosphere, living organisms, and the environment. This cycle plays a crucial role in maintaining the balance of carbon in the ecosystem. Carbon exists in the atmosphere primarily as carbon dioxide (CO₂). This abiotic carbon is the starting point for the carbon cycle.

• Carbon dioxide (CO₂) from the atmosphere is absorbed by plants during photosynthesis. Plants use CO₂ to produce carbohydrates, proteins, and fats, which serve as food for other organisms.
• Herbivores consume plants, transferring the carbon stored in plant tissues to their own bodies. Carnivores then feed on herbivores, passing the carbon further up the food chain, eventually reaching apex consumers.
• When plants and animals die, decomposers such as bacteria and fungi break down their remains, releasing carbon dioxide back into the atmosphere.
• Carbon dioxide released by respiration, decomposition, or burning of fossil fuels re-enters the atmosphere, where it is reused by plants in photosynthesis.
• This continuous exchange keeps carbon moving between the abiotic (non-living) and biotic (living) components of the ecosystem.

\[6\mathrm{CO}_{2}+12\mathrm{H}_{2}\mathrm{O}\frac{\mathrm{Sunlight}}{\text{Chlorophyll}}\mathrm{C}_{6}\mathrm{H}_{12}\mathrm{O}_{6}+6\mathrm{H}_{2}\mathrm{O}+6\mathrm{O}_{2}\uparrow\]

\[C_6H_{12}O_6+6O_2\xrightarrow{\textbf{Mitochondria}}6CO_2\uparrow+6H_2O+Energy\]

The Carbon Cycle

• Carbon is an essential element of all organic compounds, and atmospheric carbon dioxide is the main source of carbon for living organisms.
• Photosynthesis fixes carbon dioxide into organic compounds, which pass through food chains from producers to consumers.
• Respiration, decomposition, combustion of fossil fuels, and volcanic activity return carbon dioxide back to the atmosphere.
• Some carbon is stored long-term in fossil fuels and carbonate rocks, and is released slowly through burning, weathering, or acid rain.
• Human activities increase atmospheric CO₂, enhancing the greenhouse effect and leading to global warming and climate change.