The Cycling of Materials (OCR GCSE Biology A (Gateway))

Microorganisms in Material Cycling

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

The Water Cycle

• 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