Cycling and human impact on ecosystems

• Pyramid of biomass


  Shows the biomass of each trophic level in a food chain
• Biomass


  The mass of living organisms
• The total mass of organisms in each trophic level decreases going up the pyramid
• Organisms are consumed by the next trophic level

  Only about 10% of the biomass and energy is transferred up to the next level
• Reasons why only 10% of biomass and energy is transferred

  • Organisms don't eat every part of the consumed organism
  • Consumed parts may not be fully absorbed
  • Most nutrients are used for respiration rather than growth

  This is why the block in a pyramis of energy gets smaller as they go up
• Calculating efficiency of biomass transfer

  Efficiency = Biomass transferred to next level / Biomass available at previous level x 100%
• Conditions required for decomposition (decay)

  • Temperature
  • Amount of water
  • Amount of oxygen
• Decomposition takes place faster at warmer temperatures


  Decomposers use enzymes to break down plant materials, and these enzymes work faster in warm conditions
• Compost heaps tend to be quite warm because decomposers release energy when they carry out aerobic respiration
• It's important that the compost does not get too hot, as the enzymes and decomposers can denature and die
• Decomposing microorganisms work faster if the compost is moist


  Many of the chemical reactions in decay require water
• Decomposers

  • Carry out aerobic respiration, which requires a good supply of oxygen
  • The compost bin has holes in the walls to allow oxygen to enter
  • Gardeners use a gardening fork to mix the compost regularly, allowing more oxygen to pass into the center
• Anaerobic decay


  Decomposition that occurs in the absence of oxygen, producing a mixture of gases including methane
• Factors that increase the rate of decay are humidity, moisture,temperature and oxygen supply
• Carbon cycle


  The process by which carbon is continuously cycled through the environment
• Decomposers


  • Their role is to break down dead organic matter and return carbon to the atmosphere as carbon dioxide
• Carbon cycle


  1. Carbon dioxide in atmosphere

  2. Photosynthesis by plants and algae to make carbohydrates, fats and proteins

  3. Plants and algae respire, releasing some carbon dioxide back to atmosphere

  4. Plants and algae consumed by animals

  5. Animals respire, releasing carbon dioxide back to atmosphere

  6. Animals excrete waste and die

  7. Decomposers break down waste and dead remains, releasing carbon dioxide back to atmosphere

  8. Under certain conditions, carbon in dead remains can be converted to fossil fuels over millions of years

  9. Humans burn fossil fuels, releasing large amounts of carbon dioxide to atmosphere
• Photosynthesis is the only way carbon can enter the carbon cycle
• Over the last 200 years, humans have been burning huge amounts of fossil fuels, releasing large amounts of carbon dioxide to the atmosphere
• Water cycle


  1. Evaporation from oceans

  2. Water vapor travels into air

  3. Water vapor condenses to form clouds

  4. Precipitation (rain, snow, hail, sleet)

  5. Water hits ground

  6. Some evaporates back into atmosphere

  7. Some passes through rocks to form aquifers

  8. Some forms rivers/streams

  9. Rivers/streams drain back into sea

  10. Plants take up water in roots

  11. Water moves up plant in xylem

  12. Water passes out of leaf stomata as water vapor (transpiration)

  13. Animals take in water through drinking and food

  14. Animals release water in urine and feces

  15. Animals release water when exhaling
• Precipitation (rain, snow, hail, sleet) contains fresh water (does not contain salt)
• Land


  The most important limited resource that humans have access to
• Uses of land


  • Building towns and cities
  • Quarrying to extract resources from the ground
  • Farming
  • Dumping waste
• The more land used for human purposes

  The less left for other organisms
• Converting land for human use


  Often damages the environment
• Deforestation


  The cutting down of forests
• Reasons for deforestation


  • Clear land for farming
  • Grow crops for biofuels
  • Logging to obtain wood
• Deforestation


  • Reduces the ability of forests to photosynthesize and absorb carbon dioxide
  • Releases carbon dioxide when forests are burned
  • Destroys habitats and reduces biodiversity
• Peat bogs


  Areas of land with acidic, waterlogged soil where partially rotted plants form peat
• Draining peat bogs


  Allows microorganisms to decompose peat, releasing stored carbon dioxide
• Removing peat


  To use as fuel or compost also releases stored carbon dioxide
• Destruction of peat bogs


  • Happens more quickly than new ones can form
  • Destroys habitats and reduces biodiversity
• Waste from human activities is leading to pollution of water, air, and land
• Water pollution from human waste


  1. Sewage containing urine and feces released into waterways

  2. Fertilizers from farms released into rivers and streams

  3. Toxic chemicals from factories released into rivers
• Sewage and fertilizers in waterways

  Causes dissolved oxygen levels to fall, killing aquatic organisms
• Toxic chemicals released into rivers

  Can kill animals in the river
• Air pollution from human activities


  1. Burning coal in power stations releasing acidic gases causing acid rain

  2. Burning releasing smoke
• Air pollution


  Can kill plants and animals, reducing biodiversity
• Land pollution from human waste


  1. Millions of tons of waste dumped in landfills

  2. Toxic chemicals leaching out of landfills and polluting soil

  3. Toxic chemicals dumped directly onto land
• Solar radiation/light energy is the ultimate source of energy for all living organism. For this reason a food chain always starts with a producer