1. Most ecosystems rely on a supply of energy from sunlight.

2. Light energy is converted to chemical energy in carbon compounds by photosynthesis.

3. Chemical energy in carbon compounds flows through food chains by means of feeding.

4. Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

5. Living organisms cannot convert heat to other forms of energy.

6. Heat is lost from ecosystems.

7. Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

1. Quantitative representations of energy flow using pyramids of energy.

2. Use theories to explain natural phenomena- the concepts of energy flow explains the limited length of food chains.