Here is a 6 mark outline of how energy passes through ecosystems: 1. Light energy from the sun is captured by producers like plants through photosynthesis. 2. This light energy is converted to chemical energy stored in carbohydrates. 3. Primary consumers eat producers and obtain this chemical energy. 4. At each trophic level as organisms eat one another, only about 10% of the energy is transferred between trophic levels with the rest lost as heat or through feces and waste. 5. This energy loss at each level limits the length of food chains and biomass at higher trophic levels due to decreasing energy availability. 6. Heat energy produced during respiration cannot be reused by organisms and

1. 4.2 Energy flow
Nature of Science: Use theories
to explain natural phenomena—
the concept of energy flow
explains the limited length of
food chains. (2.2)
http://science.kennesaw.edu/~jdirnber/Bio2108/Lecture/LecEcology/54-01-EcosystemDynamics-AL.gifBy Darren Aherne
Essential Idea: Ecosystems require a
continuous supply of energy to fuel life
processes and to replace energy lost as heat..

2. 4.2 The Kidney & Osmoregulation Essential Idea: All animals excrete nitrogenous waste
products and some animals also balance water and solute concentrations.
Assessment Statement Guidance
4.2 U1 Most ecosystems rely on a supply of energy from
sunlight.
4.2 U2 Light energy is converted to chemical energy in
carbon compounds by photosynthesis.
4.2 U3 Chemical energy in carbon compounds flows
through food chains by means of feeding.
4.2 U4 Energy released from carbon compounds by
respiration is used in living organisms and
converted to heat..
4.2 U5 Living organisms cannot convert heat to other
forms of energy.
4.2 U6 Heat is lost from ecosystems.

3. Assessment Statement Guidance
4.2 U7 Energy losses between trophic levels restrict the
length of food chains and the biomass of higher
trophic levels..
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 S1 Skill: Quantitative representations of energy flow
using pyramids of energy.

4. 4.2 U1 Most ecosystems rely on a supply of energy from sunlight.
4.2 U2 Light energy is converted to chemical energy in carbon compounds by
photosynthesis.
http://animalstime.com/wp-content/uploads/2012/05/polar-bear.jpg
Producers capture the sun’s light energy and convert it to chemical
energy in the process of photosynthesis.
• CO2 + H2O + light  C6H12O6 + O2
Chemical energy is used to create BIOMASS.
The stored energy in biomass is passed on when consumers feed.
And converted to
chemical energy
light energy is
captured
Organisms in most ecosystems get their
energy from the sun, though
consumers get it indirectly by feeding.
Biomass is the total
dry mass of
organisms within an
area or volume.

5. 4.2 U3 Chemical energy in carbon compounds flows
through food chains by means of feeding.
http://4.bp.blogspot.com/-y_gc1LQluFk/Uyf9hKfXFeI/AAAAAAAAC6g/hzb2a419L3k/s1600/food+chain.png
A food chain shows a linear sequence of organisms, starting with a producer
and ending with a predator, that feed on each other.
• There are between 2-5 organisms in a food chain, but not more.
• Arrows show the flow of energy between organisms.
Why aren’t there more organisms in
a food chain?

6. 4.2 U4 Energy released from carbon compounds by
respiration is used in living organisms and converted to heat.
Cell respiration is the conversion of chemical energy into a form that cells
can use.
• C6H12O6 + O2  CO2 + H2O + ATP
Cell respiration releases heat when organic compounds are converted to
ATP.
Where does the heat go?
Sugar- stored
chemical energy
ATP- the energy
currency of the cell
Heat is
produced too

7. 4.2 U5 Living organisms cannot convert heat to other forms
of energy..
Organisms can convert many types of energy:
• Light energy to chemical energy in photosynthesis.
• Chemical energy to kinetic energy in muscle contraction.
• Chemical energy to electric energy in neurons.
• Chemical energy to heat energy in heat generating adipose tissue (for
homeostasis)
But once the energy becomes heat, organisms cannot convert it to any
other form of energy.

8. 4.2 U5 Heat is lost from ecosystems.
• The heat generated by cell respiration is useful to
organisms.
• It makes ectothermic (cold-blooded) animals warmer,
which allows them to be more active.
• It is used by endothermic (warm-blooded) animals to
maintain a constant body temperature in
homeostasis.
• Heat moves from warmer
areas to colder areas, so the
heat is lost to the
environment. The heat in the
ecosystem is eventually lost
into space.
Cold-blooded reptiles can be
more active when they are warm
Image: Wikipedia

9. https://www.youtube.com/watch?v=nD2-tTJg7B4
https://www.youtube.com/watch?v=v6ubvEJ3KGM
Watch these videos.

10. 4.2 Energy losses between trophic levels restrict the length of
food chains and the biomass of higher trophic levels.
Trophic level: the position of the organism in a food chain. Producers are
on the first trophic level, primary consumers on the second.
When biomass is consumed, energy is transferred.
Energy transfers between trophic levels is inefficient.
Only about 10% of the energy available at one trophic level is passed on to
the next.
Energy is lost:
• As heat from respiration
• Not consumed (bones, fur, etc.)
• As feces
http://www.mhhe.com/biosci/genbio/tlw3/eBridge/Chp29/animations/ch29
/ecosystem_organization.swf

11. From I-Biology.net

12. Problem: The production of a rainforest is 2.56 X 105 KJm-2yr-1.
Construct a pyramid of energy, assuming that 10% of energy is
passed on to each trophic level.

13. Problem: The production of a rainforest is 2.56 X 105 KJm-2yr-1.
Construct a pyramid of energy, assuming that 10% of energy is
passed on to each trophic level.
Producers: 256,000 KJm-2yr-1
Primary Consumers: 25,600 KJm-2yr-1
Secondary Consumers: 2,560 KJm-2yr-1
Tertiary Consumers: 256KJm-2yr-1
Why are food chains and biomass limited
by energy loss between trophic levels?

14. Problem: The production in a tropical rainforest biome is 2.56 X 105 KJm-2yr-1.
Construct a pyramid of energy, assuming that 10% of energy is passed on to each
trophic level.
Producers: 256,000 KJm-2yr-1
Primary Consumers: 25,600 KJm-2yr-1
Secondary Consumers: 2,560 KJm-2yr-1
Tertiary Consumers: 256KJm-2yr-1
Why are food chains and biomass limited
by energy loss between trophic levels?Because there is not much
energy available at higher
trophic levels- just 0.1% or
less
That’s why you see fewer
tigers (apex predators)
than trees (producers)!

15. Outline how energy is passed through ecosystems. (6 marks)

16. Outline how energy is passed through ecosystems. (6 marks)
The sun is the initial source of energy for most ecosystems;
Producers capture the sun’s energy in photosynthesis;
Light energy is converted to chemical energy;
Energy is passed from producers to consumers in feeding;
Energy transfer between trophic levels is inefficient/only about
10% of energy is passed between trophic levels;
Energy is lost as heat/materials not eaten/waste as feces/not
assimilated;
Organisms cannot convert heat energy to other forms of energy;
Food chains & biomass are limited by energy availability at top
trophic levels