• The individual organisms in an ecosystem need?organic molecules?to build their cells and tissues
• These molecules contain?carbon, hydrogen, oxygen, nitrogen, and phosphorus,?as well as other elements
• Because these elements are present in the?abiotic environment?(such as the?air?and?soil) in the form of?inorganic?compounds or nutrients, ecosystems depend on?producers?to transfer them into the food chain
  • Producers are?autotrophs, producing organic molecules from inorganic carbon via?photosynthesis?
    • In?terrestrial?(land-based) ecosystems, plants use CO₂?from the?air
    • In?aquatic?(water-based) ecosystems, plants use CO₂?dissolved in the water
  • Plants are also able to?absorb inorganic nutrients such as nitrates and phosphates?from the soil, incorporating them into organic molecules in their tissues as they grow
• The organic molecules in the tissues of producers can then be accessed by other organisms within the community via?food chains
  • Primary consumers?feed on producers, digesting their tissues and absorbing the organic molecules via their digestive system
  • Secondary consumers?feed on primary consumers, and so on

The inorganic nutrients originally obtained by the producer from the abiotic environment are transferred to other organisms in the community via food chains

• When inorganic nutrients enter the food chain, they are converted into organic molecules and are?locked up inside the tissues of living plants and animals
• Because the?supply of inorganic nutrients is finite, it is essential that when these organisms die the?nutrients locked up in their tissues are released
  • The organic molecules need to be converted back into inorganic nutrients that can be used by producers
• The process of breaking down the bodies of?dead organisms?and the?waste products?of living organisms is known as?decomposition,?and it enables the?cycling of nutrients
  • Detritivores?often begin the process of decomposition by breaking apart tissues
  • Saprotrophs?release enzymes that break down the organic molecules in the tissues,?releasing inorganic nutrients
  • While saprotrophs absorb some of these nutrients themselves, what is left in the soil becomes available for producers

The cycling of nutrients in an ecosystem

• In a functioning?ecosystem, the elements that living organisms need are?constantly recycled
  • Producers?access?inorganic nutrients?from the abiotic environment and convert them into?organic molecules
  • Consumers?gain organic nutrients from?ingesting the tissues?of producers and other consumers
  • Detritivores?and?saprotrophs?break down the organic molecules?in dead tissues and waste matter, making them?available again to producers
• Provided that the conditions are right and this cycling process continues, ecosystems can be?sustainable?over long periods of time
• If nutrient cycling stops then an ecosystem can only be productive until the?finite supply of inorganic nutrients runs out
  • Without the process of decomposition, nutrients?remain locked up?in dead tissues and cannot re-enter the food chain
• Nutrient cycling might stop if environmental conditions become?unsuitable for decomposition
  • Climate change?might cause an ecosystem to become too dry for saprotrophs to survive
  • Harvesting?or?deforestation?removes organic matter from the environment and leaves nothing for saprotrophs to digest, meaning that the nutrients contained within this organic matter are not recycled back into the ecosystem and are instead completely removed from the ecosystem