4.2 Energy Flow

Essential Idea

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

Understandings

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.

Applications

• None

Skills

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

Guidance

1. 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.

2. Pyramids of energy should be drawn to scale and should be stepped, not triangular. The terms producer, first consumer, second consumer, etc. should be used, rather than first trophic level, second trophic level etc.

3. 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.

Key Vocabulary

• Energy

  • Light

  • Chemical

  • Heat

• Food chain

Textbook Reading and/or Activities

Click HERE for a pdf of chapter 4.

• Pages 195-202

  • Worked Example (p.200)

  • Nature of Science (p.200)

  • Nature of Science (p.201)

  • Exercises (p.202)

Notes

4.2 Energy Flow

A detailed set of notes, prepared by Bob Smullen, examining U1-U7 and S1.

i-Biology Notes

A detailed set of notes, created by Stephen Taylor, examining U1 - U7 and S1.

i-Biology Notes

Another detailed set of notes, prepared by Stephen Taylor, that includes material on the whole of Topic 4. Worth checking out.

4.1 & 4.2 Study Questions

A series of questions, prepared by Jacob Cedarbaum, to help you prepare for the relevant sections of the IB Exam. This is VERY GOOD practice.

Bob Smullen Ecology Review

A series of questions, prepared by Bob Smullen, to help check your understanding of both Topic 4 and Option C based on Ecology. This is VERY GOOD practice.

IB Ecology Review

A series of questions, prepared by Jacob Cedarbaum, to help check your understanding of the IB learning expectations for all of Topic 4. Check your work when you're done HERE. This is VERY GOOD practice.

Learning Activities

Worksheet - Food Chains & Food Webs

This activity, modified from Biology Junction and Enchanted Learning, will help students understand they various parts of a food chain/web and how energy flows through the system in a linear manner.

Supplemental Reading