Recycling within an ecosystem

Decomposition

• Chemical process in which a compound is broken down into smaller molecules or constituent elements
• Decomposer = an organism that feeds on and breaks down dead plant and animal matter thus turning organic compounds back to nutrients to be used again
• Mostly microscopic fungi and bacteria
• They are also called saprotrophs because they get their energy from dead material
• They digest food externally by excreting enzymes and then absorb the products
• Almost as a byproduct, they release inorganic compounds and elements back to the environment
• Detritivores are another class of organism that are involved --> they help speed up the decaying process as they feed on dead and decaying matter 
  • They break it down into smaller pieces which increases the surface area for the decomposers
  • They perform internal digestion

Recycling nitrogen

• Essential element for amino acids and nucleic acids in both plants and animals
• Abundant in the atmosphere as nitrogen gas but this cannot be taken up by plants so bacteria or lightning have to convert it first
• Nitrogen fixation
  • Free-living bacteria like Azotobacter use nitrogenase to fix atmospheric nitrogen with hydrogen to produce ammonium ions
  • Mutualistic bacteria like Rhizobium use nitrogenase to fix atmospheric nitrogen with hydrogen to produce ammonium ions --> symbiotic relationship with plants, live in the root nodules and exchange the ammonium ions for carbohydrates made by the plant
  • Lightning and the Haber process also fix nitrogen into ammonium ions
• Nitrification
  • Ammonium compounds in the soil are converted to nitrogen-containing molecules that plants can use
  • Free living nitrifying bacteria like Nitrosomonas oxidise ammonium ions into nitrites
  • Nitrobacter oxidise nitrites to nitrates which are highly soluble so can be taken up by the plant
• Denitrification
  • Denitrifying bacteria in the soil convert nitrates back to nitrogen gas when there's an absence of oxygen --> nitrates are used by the bacteria as a source of energy
• Ammonification
  • The process by which decomposers convert nitrogen-containing compounds to ammonium ions

Recycling carbon

• Oceans act as carbon stores
• Photosynthesis removes carbon from the atmosphere 
• Producers and consumers release carbon through respiration
• Carbon passes from producers to consumers through feeding
• After both die, their stored carbon is released by decomposers
• The burning of fossil fuels releases more carbon into the atmosphere
• Levels fluctuate throughout the day as plants only photosynthesise when it's light but respire at almost all times (unless its a cactus) --> carbon dioxide levels are lower in the summer as its light for longer so more photosynthesis occurs
• Over the past 200 years atmospheric carbon dioxide has increased significantly because
  • the combustion of fossil fuels rocketed in the Industrial Revolution and has remained high since then
  • deforestation has removed many of the plants that take the carbon dioxide out of the air
• Increased carbon dioxide traps more thermal energy in the atmosphere thereny causing global warming and climate change
• The amount of carbon dioxide dissolved in the oceans is affected by the temperature of the water (higher temperature = less gas) so global warming decreases the ability of the oceans to act as carbon banks