8.2.3

Biomass & Food Chains

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Plant Biomass

Plants are central to all ecosystems because they produce biomass through photosynthesis.

Producing biomass

Producing biomass

  • Green plants are called producers because they use light energy to produce organic molecules (e.g. carbohydrates).
  • Organic molecules produced by the plant are used in two ways:
    • As respiratory substrates.
    • To make other biological molecules (carbohydrates, proteins and lipids). These biological molecules form new biomass.
Biomass in the food chain

Biomass in the food chain

  • Biomass is the chemical energy store for an organism.
  • Energy stored within biomass can be passed along the food chain to different trophic levels.
Food chains

Food chains

  • Food chains show how energy flows within a biological community.
  • Producers (plants and algae) are at the base of all food chains. They produce biomass.
  • Consumers rely on producers as their source of energy. When they eat plants and algae, the chemical energy stored in their biomass is transferred.

Measuring Biomass

We can measure biomass in terms of dry mass of tissue per unit area or the mass of carbon in an organism. Calorimeters are a piece of apparatus that are used to measure biomass.

Dry mass of tissue per unit area

Dry mass of tissue per unit area

  • Dry mass is the mass of an organism after its water has been removed.
  • To remove the water, the organism is dried in an oven for several days.
  • The dry mass of a sample can be used to estimate the total dry mass of a population or given area.
  • Dry mass is usually measured in grams or kilograms per meter squared (g m-2, kg m-2).
Mass of carbon

Mass of carbon

  • This is a measure of the mass of carbon an organism has.
  • The water content of an individual is not taken into account.
  • The mass of carbon is usually about half the dry mass.
Calorimetry

Calorimetry

  • The energy contained within dry biomass can be measured using a calorimeter.
  • A calorimeter burns biomass and calculates the chemical energy released per gram.
    • This calculation is made by measuring the change in temperature of a known volume of water that happens as a result of the sample being burned.
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Practice questions on Biomass & Food Chains

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of the following statements about plant biomass are true?True / false
  2. 2
    Where does energy flow within food chains?Multiple choice
  3. 3
    What can the energy contained within dry biomass be measured with?Multiple choice
  4. 4
    What are the two methods for measuring biomass?Fill in the list
  5. 5
    Which of the following statements about measuring biomass are true?True / false
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Energy Flow

Heterotrophs & Autotrophs