Biogeochemical Cycles: Carbon Cycle

Biogeochemical Cycles

The Carbon Cycle

• Carbon is the backbone of biological molecules, including carbohydrates, lipids, proteins, and nucleic acids.
• Carbon dioxide (CO2) is a gas in the atmosphere, making up around 0.04% of the gases.
• Plants and algae absorb CO2 through photosynthesis, producing glucose and storing carbon.
• Herbivores consume plants and algae, passing on stored carbon to their body mass.
• Respiration by living organisms releases CO2 back into the atmosphere.
• Decomposers break down dead organisms, releasing CO2 back into the atmosphere.
• Fossilization can produce fossil fuels, such as coal, oil, and gas, which are a store of carbon.
• Human activities, like burning fossil fuels, release CO2 into the atmosphere.

The Nitrogen Cycle

• Nitrogen is an essential component of proteins and nucleic acids, like DNA and RNA.
• Nitrogen is abundant in the atmosphere, but in a form that cannot be used by living organisms.
• Nitrogen fixation by bacteria converts nitrogen into ammonium ions (NH4+).
• Nitrification occurs in two stages: ammonium ions are converted into nitrites by Nitrosomonas, and then into nitrates (NO3-) by Nitrobacter.
• Plants absorb nitrates through assimilation, and animals consume them through the food chain.
• Decomposers break down nitrogen compounds into ammonium ions, which can be nitrified again.
• Denitrifying bacteria can convert nitrates back into nitrogen gas in anaerobic conditions.

The Water Cycle

• Water is essential for life, making up over 70% of cells.
• Water is a solvent, temperature buffer, and aids in aerobic cellular respiration.
• Most water is found as saltwater (97.5%), with only a small fraction available as freshwater.
• Liquid water is evaporated from oceans, lakes, and puddles by heat energy from the Sun, turning into water vapor.
• Water vapor cools and condenses back into water, forming clouds.
• Clouds can be blown by wind and transported to other areas, eventually releasing water as precipitation.
• Precipitation can be absorbed into the ground through percolation, or flow on the surface as surface runoff.
• Plants transport water from their roots to their leaves through the transpiration stream, eventually releasing it back into the atmosphere as water vapor.

The Phosphorus Cycle

• Phosphorus is a limiting nutrient in ecosystems, often in short supply.
• Phosphorus is found naturally as phosphate ions (PO43-), which form compounds with other elements.
• Phosphates are released into the soil through weathering and surface runoff.
• Plant roots absorb phosphates, which are passed on to animals through the food chain.
• Decomposers break down dead organisms, releasing phosphates back into the soil and water.
• Artificial fertilizers contain phosphates, which can enter waterways through surface runoff and sewage.
• Algae and other photosynthetic marine organisms take up dissolved phosphates, passing them on through marine food chains.