Energy flows through ecosystems from sunlight through photosynthesis by producers to consumers in a food chain. Only about 10-20% of energy is transferred between trophic levels, with the rest lost as heat through respiration. This loss of energy at each trophic level restricts food chain length and biomass of higher levels. Ecosystems rely on the continuous input of solar energy to replace energy lost as heat and sustain life processes.

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

2. Understandings, Applications and Skills
Statement Guidance
4.2 U.1 Most ecosystems rely on a supply of energy from sunlight
4.2 U.2 Light energy is converted to chemical energy in carbon compounds by
photosynthesis
4.2 U.3 Chemical energy in carbon compounds flows through food chains by means of
feeding. [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.]
4.2 U.4 Energy released from carbon compounds by respiration is used in living
organisms and converted to heat.
4.2 U.5 Living organisms cannot convert heat to other forms of energy.
4.2 U.6 Heat is lost from ecosystems.
4.2 U.7 Energy losses between trophic levels restrict the length of food chains and the
biomass of higher trophic levels. [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.]
4.2 S.1 Quantitative representations of energy flow using pyramids of energy. [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.]

3. 4.2 U.1 Most ecosystems rely on a supply of energy from sunlight
An open system makes it possible of maintain a stable ecosystem, with a lose of 90% of
all the energy input. Due to the Sun’s constant supply of energy back into the system.
Energy is an open system on Earth

4. Sunlight is the initial energy source for
almost all communities
• Energy flows through the food chain, being lost at each stage
due to respiration.
4.2 U.1 Most ecosystems rely on a supply of energy from sunlight

5. 4.2 U.2 Light energy is converted to chemical energy in carbon
compounds by photosynthesis
• The process by which plants, autotrophic light
energy (photons) to make sugars and other
organic food molecules from carbon dioxide and
water

6. 4.2 U.3 Chemical energy in carbon compounds flows through food
chains by means of feeding
Chemical energy in carbon compounds flows through food chains by means of feeding.
•1º consumers feed on the producers. Only around 10%-20% of the energy from the producer is
passed on to the 1º consumers. The rest of the energy islost as heat through cell respiration,
death and waste.
•2º consumers feed on the 1º consumers. Again only 10%-20% of the energy is passed on to the
next level, with the rest lost as heat through respiration, death, and waste.
•3º consumers feed on 2º consumers. 10%-20% is passed on to the tertiary consumer and the
rest is lost as heat, death and waste.

7. 4.2 U.4 Energy released from carbon compounds by respiration is used
in living organisms and converted to heat.
• Organisms need cellular energy for
cellular activities (MR. H GREN)
• ATP provides the energy needed for
these cellular activities
• ATP is produced through cellular
respiration, is an exothermic (heat is
produced as a waste product) and the
energy released is used in endothermic
phosphorylation reactions to create
ATP.
• ATP can be used quickly for the cellular
activities listed above.
• These reactions 38% efficient,
therefore some of the energy produced
in these oxidation reactions is lost as
heat.
• *Burning gas in your car to move it
is about 25% efficient

8. 4.2 U.5 Living organisms cannot convert heat to other forms of energy.
• Organisms can perform a variety of energy conversions, such as light
to chemical energy during photosynthesis, chemical energy to
KE during muscle contractions, chemical energy to electrical
energy in nerve impulses and chemical energy to heat energy in
heat-generating adipose tissue
• Organisms cannot turn heat energy into any other forms of energy

9. 4.2 U.6 Heat is lost from ecosystems
• Heat resulting from
cellular respiration makes
an organism warmer.
Cold-blooded organisms
can become more active,
while warm blooded
animals can increase
their rate of heat
generation in order to
maintain their in internal
body temperature
• Eventually though, since
heat passes from warmer
to colder bodies, all heat
is lost from the
ecosystem

10. Energy Flow Through
Ecosystems
4.1 U.7 Energy losses between trophic levels restrict the length of food
chains and the biomass of higher trophic levels.

11. Energy Pyramid
• The greatest amount of energy in a community is present
in the organisms that make up the producer level.
• Only a small portion of this energy is passed on to primary
consumers, and only a smaller portion is passed on to
secondary consumers (on average, only about 10% of the
energy).
• A pyramid of energy can be used to illustrate the loss of
usable energy at each feeding level.
4.2 S.1 Quantitative representations of energy flow using pyramids of
energy.

12. Pyramids of energy
• Show the flow of energy between trophic levels
• Measured in units of energy per unit area per unit time. KJ m-2
y-1
• The transfer of energy is never 100% efficient
4.2 S.1 Quantitative representations of energy flow using pyramids of
energy.

13. THE 10% RULE
and
ECOLOGICAL
PYRAMID
4.2 S.1 Quantitative representations of energy flow using pyramids of
energy.

14. Trophic Levels
Notice that only 10% is moved to the next level.
Where does the rest go?
4.2 S.1 Quantitative representations of energy flow using pyramids of
energy.

15. Bibliography /
Acknowledgments