The Cycling of Materials (OCR Gateway GCSE Biology: Combined Science)

Material cycling

• Biological molecules have to be broken down and re-used on a constant basis
• The breakdown products are the building blocks for future life
• This is called material cycling
• Material cycling prevents the constant build-up of dead biomass that has no further use to any organisms
  • Without material cycling, we would be several kilometres deep in dead organisms, and certain biological materials will have run out a long time ago
• Material cycling takes place between the atmosphere, biomass, the land and oceans
  • A particular atom, say a carbon atom, will have constantly cycled around as part of various compounds since the beginning of life
  • And will continue to cycle after humans have become extinct
  • Microorganisms will continue to facilitate material cycling
  • They are believed to be the first life forms to have evolved, therefore crucial to all life forms
• Many different materials cycle through the abiotic and biotic components of an ecosystem
  • The main examples of cycled materials are water, nitrogen and carbon
• Microorganisms (mainly bacteria and fungi) play a major role in the cycling of materials through an ecosystem
  • Particularly in decomposition and decay

Roles of microorganisms in material cycles

• Microorganisms play a crucial role in material cycling
  • Without them, ecosystems would not exist as we know them today
  • Lack of microorganisms would severely upset the ecological balance of ecosystems
• Microorganisms play little direct part in the water cycle
  • This involves evaporation, condensation, precipitation and flow of fresh water through ecosystems
• Microorganisms play the following key roles in the nitrogen cycle
  • Decomposers
  • Fixing nitrogen gas (N₂) from the atmosphere
  • Nitrification (turning N₂ into useful nitrogen-containing ions like nitrates)
  • Denitrification (returning N₂ to the atmosphere from organic matter)
• In the carbon cycle, microorganisms are involved in
  • Photosynthesis
  • Assisting animals to metabolise organic compounds e.g. cellulose
  • Decomposition
  • Decay

• Water molecules move between various locations – such as rivers, oceans and the atmosphere – by specific processes
• This is possible because water can exist in all three states (solid, liquid and gas) in Earth's climate

The importance of the water cycle

• All life on Earth depends upon water for a variety of reasons
  • This includes being a major raw material for photosynthesis
• The water cycle, therefore, is a fundamental process for all living things as it distributes fresh water globally providing us with clean water for drinking
• It refreshes the flow of nutrients and in doing so, maintains habitats

The water cycle