BRAINCAKENutrient Recycling
Energy flows through an ecosystem in one direction: it enters as light and leaves as heat, and it is never recycled. Nutrients such as carbon, nitrogen and phosphorus are different. The Earth has a fixed amount of each, so they must be recycled between living organisms and the environment.
When organisms die, or produce waste such as faeces, urine and shed leaves, the nutrients are locked up in complex organic molecules (proteins, nucleic acids, carbohydrates, lipids). Plants cannot absorb these, so they must be broken down.
Decomposers are mainly bacteria and fungi. They are saprobionts: they secrete enzymes onto the dead material, which digest it outside their cells. This is extracellular digestion. They then absorb the soluble products, such as sugars and amino acids, and use them in respiration and growth.
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More in The Efficiency of Ecosystems
- Gross Primary Productivity
- Net Primary Productivity
- The Limitations of Efficiency Calculations
- Energy Transfer and Food Chain Length
- Conditions for Recycling Nutrients
- Microorganisms in the Nitrogen Cycle
- Microorganisms in the Carbon Cycle
- Short-term Carbon Sinks
All 20 lessons in The Efficiency of Ecosystems · All Edexcel A-level Biology topics