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 bars in the pyramid get smaller as you go up the trophic levels
• 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
• 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
• It's important that gardeners do not allow a compost heap to dry out
• 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
• Small-scale biogas generators use plant materials such as food waste or animal manure to produce biogas under anaerobic conditions
• Decomposers produce biogas under anaerobic conditions
• 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
• Respiration and breathing are not the same thing
• Decomposers are extremely important as they cycle materials through an ecosystem and return carbon to the atmosphere as carbon dioxide
• Decomposers also release mineral ions to the soil
• If decomposers cannot function effectively due to lack of oxygen, carbon in dead remains can slowly be converted to fossil fuels
• 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
• Almost all water on Earth is found in the oceans and is salt water
• Energy from the Sun causes the water to evaporate from the surface of the sea
• Water vapor cools down and condenses to form clouds
• Precipitation (rain, snow, hail, sleet) contains fresh water (does not contain salt)
• Some of the water that hits the ground evaporates back into the atmosphere as water vapor
• Some of the water passes through rocks and forms aquifers
• A lot of the water forms rivers or streams
• The water in rivers and streams eventually drains back into the sea
• Plants take up water in their roots and this water moves up the plant in the xylem
• The water passes out of the leaf stomata as water vapor (transpiration)
• Animals take in water through drinking and in their food
• Animals release water in their urine and feces, and when they exhale