Ecosystems

• Biomass


  The amount of energy that an organism contains
• Trophic levels


  Stages in the food chain
• Ecological efficiency


  The efficiency in which biomass or energy is transferred from one trophic level to the next
• Biomass transfer through an ecosystem

  1. Producers

  2. Primary consumers

  3. Secondary consumers

  4. Tertiary consumers
• Ecological efficiency is often considered in percentage terms
• Producers


  Plants that produce food through photosynthesis
• Energy/biomass transfer in a food chain

  1. Producers get eaten by primary consumers

  2. Primary consumers get eaten by secondary consumers

  3. Secondary consumers get eaten by tertiary consumers
• Primary consumers


  Herbivores that eat the producers
• The amount of energy/biomass from producers that actually gets used by primary consumers is never 100%, usually around 10-20%
• Reasons for energy/biomass loss

  • Not all light energy is used in photosynthesis
  • Other factors affecting photosynthesis rate (e.g. water availability)
  • Energy used up within photosynthesis reactions
  • Respiration by consumers releases thermal energy
  • Consumers excrete undigested food
• Farmers want to increase energy/biomass transfer efficiency


  Measures to do this include: ensuring optimal conditions for photosynthesis, keeping animals indoors to reduce respiration, providing high energy content feed, preventing animal illness, limiting animal movement
• Useful energy


  Energy used to build body/biomass
• Secondary consumers


  Organisms that eat the primary consumers
• Biomass can be correlated to energy content
• Tertiary consumers


  Organisms that eat the secondary consumers
• The food chain can be represented by a pyramid with the most producers at the bottom and fewer organisms at each higher trophic level
• Methods to maximize ecological/energy transfer efficiency include: ensuring optimal conditions for photosynthesis, keeping animals indoors, providing high energy feed, preventing animal illness, limiting animal movement, genetic engineering/selective breeding
• Biomass


  Mass of living material in an area or in particular organisms without their water content
• Water content is not included in biomass as it can fluctuate and does not represent the true energy content
• Measuring biomass


  1. Collect sample

  2. Kill organism

  3. Dry in oven at 80°C until mass stays constant
• Calorimeter


  Machine that measures the energy content (calories) of an organism
• Units for biomass


  Grams per meter squared for land animals, grams per meter cubed for marine animals
• Biomass is related to the energy content of an organism
• Decomposers


  Organisms that feed on dead organic matter and turn them into inorganic substances
• Decomposers


  • They secrete enzymes outside their body to digest the food
  • They do external digestion rather than internal digestion
• Detritivores


  Organisms that feed on dead organic matter
• Detritivores


  • They do internal digestion
  • They increase the surface area of the food by munching on it, which speeds up decomposition
• Carbon cycle


  1. Producers take in carbon dioxide for photosynthesis

  2. Consumers release carbon dioxide through respiration

  3. Decomposers release carbon dioxide when digesting organic matter

  4. Fossil fuels are burned, releasing carbon dioxide into the atmosphere

  5. Carbon is recycled between producers, consumers, and the atmosphere
• All organic matter contains carbon, which is recycled through the carbon cycle
• The key molecule in the carbon cycle is carbon dioxide
• Feeding is one of the processes by which carbon is transmitted through the carbon cycle
• When organisms die, decomposers digest the organic matter, releasing carbon dioxide
• Some of the remaining undigested organic matter can become fossil fuels
• Burning fossil fuels releases carbon dioxide into the atmosphere