unit 3

• Biogeochemical cycles


  Cycles where matter (the material of which organisms are composed) moves from one part of the ecosystem to another, i.e. from one organism to another and from living organisms to the abiotic environment and back again
• Biogeochemical cycles are important to living things because they allow the cycling of nutrients and materials essential for life
• Macronutrients


  Nutrients an organism needs in large amounts to live, grow or reproduce
• Micronutrients


  Nutrients an organism needs in small amounts to live, grow or reproduce
• Major biogeochemical cycles


  • Carbon cycle
  • Nitrogen cycle
  • Phosphorus cycle
  • Water cycle

  
• Carbon


  The basic building block for carbohydrates, fats, proteins and nucleic acids such as DNA
• Carbon source for living organisms


  Carbon dioxide present in the atmosphere or dissolved in surface waters

  
• Major carbon reservoirs


  • Earth's rocks
  • Fossil fuels
  • Ocean beds

  
• Carbon cycle


  1. Photosynthesis

  2. Respiration and decomposition

  3. Combustion

  4. Diffusion

  
• Photosynthesis is the only natural process that removes carbon dioxide from the environment
• Excess carbon dioxide has been implicated as a factor causing global warming

  
• Humans affect the carbon cycle through deforestation, clearing of grasslands and green areas, and burning of fossil fuels and wood

  
• Nitrogen fixation


  Conversion of gaseous nitrogen (N2) to ammonia (NH3)

  
• Nitrification


  Conversion of ammonium (NH4) and ammonia (NH3) to nitrate (NO3)
• Assimilation


  Plants absorb nitrate or ammonia and incorporate nitrogen into proteins and nucleic acids
• Ammonification


  Conversion of biological nitrogen compounds into ammonia
• Denitrification


  Reduction of ammonia/ammonium into nitrate and then nitrite to gaseous nitrogen
• Nitrogen fixing bacteria, nitrifying bacteria, ammonifying bacteria, and denitrifying bacteria are involved in the nitrogen cycle

  
• Humans affect the nitrogen cycle through excessive use of nitrogen-based fertilizers and adding nitrogenous gases to the atmosphere by burning fossil fuels

  
• Excessive nitrogen and phosphorus can cause eutrophication in water bodies

  
• Phosphorus cycle


  1. Weathering and erosion

  2. Runoff

  3. Absorption and assimilation

  4. Consumption

  5. Decomposition

  
• Phosphorus is a non-renewable resource
• Humans disrupt the phosphorus cycle through excessive mining of phosphate rocks, shipping of food from farms to cities, and use of excessive inorganic phosphorus fertilizers

  
• The phosphorus cycle may often be considered as coming to a dead end because phosphorus washed into the ocean can be lost from biological cycles for millions of years

  
• Hydrological (water) cycle


  1. Precipitation

  2. Evaporation

  3. Transpiration

  4. Condensation

  5. Runoff

  6. Infiltration

  7. Sublimation

  
• Only about 0.024% of Earth's water supply is available and accessible as liquid freshwater
• Humans affect the hydrologic cycle by withdrawing large quantities of freshwater faster than it can be replaced, clearing vegetation, and creating concrete barriers that hinder infiltration
• Precipitation


  Water moving from the atmosphere to the land and ocean in the form of rain, snow, sleet, hail