Food chains and food webs

• Why only 1-3% of the Sun's energy is converted into organic matter:

  • over 90% is reflected back to space or absorbed by the atmosphere
  • not all wavelengths can be used for photosynthesis
  • may not fall on a chlorophyll molecule
  • another factor is limiting the rate of photosynthesis
• Energy is transferred through trophic levels

  producer -> primary consumer -> secondary consumer -> tertiary consumer
• Biomass is the total mass of biological material derived from living or recently living organisms in a specific area at a given time, not including water
• Biomass is measured as dry mass per given area per given time
• Using a calorimeter

  • sample is dried by heating in an oven to evaporate all the water in the sample
  • sample is weighed, placed in a cup and ignited in an oxygen-rich atmosphere
  • heat from combustion is transferred to the water
  • thermometer measures temperature change
• energy = (specific heat capacity x volume x temperature change)/mass of sample