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4.2 Energy flow

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Description

Nature of science:
Use theories to explain natural phenomena—the concept of energy flow explains the limited length of food chains. (2.2)
Understandings:
  • Most ecosystems rely on a supply of energy from sunlight.
  • Light energy is converted to chemical energy in carbon compounds by photosynthesis.
  • Chemical energy in carbon compounds flows through food chains by means of feeding.
  • Energy released from carbon compounds by respiration is used in living organisms and converted to heat.
  • Living organisms cannot convert heat to other forms of energy.
  • Heat is lost from ecosystems.
  • Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.
Applications and skills:
  • Skill: Quantitative representations of energy flow using pyramids of energy.
Guidance:
  • Pyramids of number and biomass are not required. Students should be clear that biomass in terrestrial ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other waste products, such as urea.
  • Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer and second consumer and so on should be used, rather than first trophic level, second trophic level and so on.
  • The distinction between energy flow in ecosystems and cycling of inorganic nutrients should be stressed. Students should understand that there is a continuous but variable supply of energy in the form of sunlight but that the supply of nutrients in an ecosystem is finite and limited.
 International-mindedness:
  • The energetics of food chains is a factor in the efficiency of food production for the alleviation of world hunger.
Utilization:
Syllabus and cross-curricular links:
Biology
Topic 2.8 Cell respiration
Topic 2.9 Photosynthesis
Physics
Topic 2.3 Work, energy and power
Topic B.2 Thermodynamics
Environmental systems and societies
Topic 2.3 Flows of energy and matter

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