Cycles in Ecosystems
How nutrients recycle through living and non-living components
Nutrient Recycling Systems
Understanding how carbon, nitrogen, and water cycle through ecosystems
Carbon atoms cycle continuously between living organisms and the atmosphere. Carbon dioxide (CO₂) is removed from the air during photosynthesis by plants, which convert it into glucose through carbon fixation. This carbon becomes part of plant tissues and moves through food chains when herbivores eat plants and carnivores eat herbivores.
Carbon returns to the atmosphere through several processes. Respiration by all living organisms releases CO₂ as they break down glucose for energy. When organisms die, decomposers (bacteria and fungi) break down dead material, releasing CO₂ through decomposition. Human activities add carbon through combustion of fossil fuels, which releases stored carbon accumulated over millions of years.
Nitrogen is essential for making proteins and nucleic acids (DNA and RNA), but atmospheric nitrogen gas (N₂) cannot be used directly by most organisms. Nitrogen fixation by specialized bacteria in soil and root nodules converts N₂ into ammonia (NH₃), making it available to plants.
Other bacteria perform nitrification, converting ammonia into nitrates that plants absorb through roots. Animals obtain nitrogen by eating plants or other animals. When organisms die or produce waste, decomposers break down nitrogen compounds back into ammonia. Denitrifying bacteria complete the cycle by converting nitrates back into N₂, returning nitrogen to the atmosphere.
Water continuously moves through ecosystems via evaporation from oceans, lakes, and soil surfaces into water vapor. Plants also release water vapor through transpiration. Condensation forms clouds as water vapor cools in the atmosphere.
Water returns to Earth's surface through precipitation (rain, snow, hail), where it collects in bodies of water or soaks into soil. This water is used by living organisms before eventually evaporating again, completing the cycle.
These biogeochemical cycles are essential for maintaining ecosystem balance. They recycle nutrients so they remain available to living organisms rather than being permanently locked away. Without these cycles, essential elements like carbon and nitrogen would become depleted, making life impossible. Decomposers play a crucial role by breaking down dead material and returning nutrients to soil and atmosphere where they can be reused by producers.
Step 1 of 5: Photosynthesis
Carbon CyclePlants absorb CO₂ from atmosphere and convert it to glucose
CO₂ + H₂O + light → C₆H₁₂O₆ + O₂
Question: Describe how carbon moves through a forest ecosystem, including all major processes.
Answer:
- Photosynthesis: Trees absorb CO₂ from atmosphere and use sunlight to convert it into glucose, storing carbon in leaves, stems, and roots
- Feeding: Carbon moves to herbivores (deer, insects) when they eat plant material, then to carnivores (foxes, owls) that eat herbivores
- Respiration: All forest organisms (plants, animals, decomposers) release CO₂ back to atmosphere during cellular respiration
- Death and Decomposition: When organisms die, decomposers (fungi, bacteria) break down dead leaves, wood, and animal bodies, releasing CO₂
- Combustion: Forest fires or human burning of wood releases stored carbon as CO₂
The cycle continues as released CO₂ becomes available for photosynthesis again, maintaining carbon balance in the ecosystem.
Which process removes CO₂ from the atmosphere?