4.2: Energy flow

Key Vocabulary

Retrieval practice and prior learning

Essential idea: Ecosystems require a continuous supply of energy to fuel life processes and to replace energy lost as heat.

Nature of science: Use theories to explain natural phenomena—the concept of energy flow explains the limited length of food chains. (2.2)

U1: Most ecosystems rely on a supply of energy from sunlight.

Exercise 1: Read page 213 of Allott & Mindorff and answer the following questions:

1. What is the initial source of energy for most ecosystems? (Can you remember the definition of an ecosystem? Can you research any ecosystems that don't require sunlight?)

2. How is sunlight energy harvested? 

3. What is the difference between the words "autotroph" and "producer"?

4. How are heterotrophs indirectly dependent on sunlight energy?

5. Why do the redwood forests of California produce more energy for consumers than the Sahara desert?

Exercise 3: Complete the following steps

U2: Light energy is converted to chemical energy in carbon compounds by photosynthesis.

• Indicate on your pyramid where light energy enters the ecosystem

U3: Chemical energy in carbon compounds flows through food chains by means of feeding.

• Indicate where feeding occurs on your pyramid

U4: Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

U5: Living organisms cannot convert heat to other forms of energy.

U6: Heat is lost from ecosystems.

• Indicate on your diagram how energy is lost from ecosystems

U7: Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

• Read the appropriate pages of your textbook and answer the following questions:

  • Why is energy lost between trophic levels in an ecosystem?

  • Why does this restrict the length of food chains within food webs?

• 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.