2- The Transfer of Biomass

• Biomass


  The mass of living material of the organism or tissue<|>The chemical energy that is stored within the organism or tissue
• Biomass can be measured in terms of

  • The dry mass of an organism or tissue (in a given area)
  • The mass of carbon that an organism or tissue contains
  • The mass of carbon that a sample (i.e. an organism or tissue) contains is generally taken to be 50% of the dry mass of the sample
  • The chemical energy content of the organism when burned in pure oxygen
• Dry mass


  The mass of the organism or tissue after all the water has been removed
• Estimating biomass of a population


  1. Find dry mass of single organism

  2. Multiply by number of organisms
• Estimating biomass of organisms in a larger area

  1. Find dry mass of organisms in a given (smaller) area

  2. Multiply by size of larger area
• Biomass can change over time
• Biomass is sometimes given with units of time as well
• Calorimetry


  Used to estimate the chemical energy stored in dry biomass
• Energy transfer is the main goal of feeding relationships
• Finding the dry mass of a plant sample

  1. Weigh the crucible without the sample

  2. Place the sample in the crucible

  3. Place the crucible in the oven at low temperature

  4. Remove and weigh the crucible at regular intervals

  5. Once mass is constant, the sample is fully dehydrated
• Finding the energy released by a sample of plant biomass

  1. Burn the dried sample in a calorimeter

  2. Measure the change in temperature of the water

  3. Use the temperature change to estimate the chemical energy stored within the sample

  
• Joule (J)


  The amount of heat needed to raise the temperature of 24 g or 0.24 cm3 or 0.24 ml of water by 1 °C
• Kilojoule (kJ)


  The amount of heat needed to raise the temperature of 240 g or 240 cm3 or 240 ml of water by 1 °C (or to raise the temperature of 24 g of water by 10 °C)
• It can take a long time to fully dehydrate a plant sample to find its dry mass
• Precise equipment is needed, which may not be available
• The more simple and basic the calorimeter, the less accurate the estimate will be for the chemical energy contained within the plant sample