International School Hannover Region
Science Department – Grade 9 Science - Biology
ECOLOGY TOPIC
Key Questions:
How can the status of an environment be determined?
In what ways do man’s activities affect the health of the environment?
Part 2 – Pyramid of Energy (Food Webs/Trophic levels was Part 1)
You have seen that:
The herbivore populations (sparrows, hummingbirds, rabbits, chipmunks, butterflies, bees and grubs) obtain their energy (and nutrients) by eating
different parts of the plants.
In turn the carnivore populations (cats, preying mantis', frogs, robins, hawks) feed on these herbivores and in some cases on other carnivores.
Scavengers eat dead organisms.
There may also be a very significant decomposer presence with primary and secondary detritus feeders (bacteria, fungi, moles, ants, earthworms).
Biomass Production
The food required by the herbivore populations is provided by biomass, the 'producers' in the food web. Primary production is generation of biomass
through photosynthesis. The highest producers of biomass are:
Tropical rain forests
2000 g/m²/yr of biomass
Swamps and marshes
2500 g/m²/yr of biomass
Algal beds and reefs
2000 g/m²/yr of biomass
River estuaries
1800 g/m²/yr of biomass
Others include
Temperate forests
1200 g/m²/yr of biomass
Cultivated lands
600 g/m²/yr of biomass
while lowest producers are deserts and frozen areas (less than 200 g/m²/yr of biomass).
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Creating Pyramids of Energy
TASK 1
Here is a simple method of demonstrating the energy transformations in an ecosystem using a pyramid. Complete this exercise
Steps for Energy Pyramid One – general method
1. Cut out each of the strips on your “Pyramid of Energy: Feeding levels” sheet on page 6. The strips are the same size and have a line in the
middle to show you where the centre of the strip is. You create the pyramid by cutting the strips to the correct length and then lining them up
at their centers.
2. Label one strip “Producers”
Measure the length of this strip in millimeters and record this number in the Pyramid of Energy data table. This will represent the
hypothetical number of kilocalories present at this feeding level.
3. Label a second strip “Primary Consumers”
Only 10% of the energy present in the biomass of the producers is converted into animal biomass. Therefore the length of the Primary
Consumer strip can only be 10% of the length of the Producer strip. Determine how many millimeters that is, write it in your table and then
cut the strip. Keep the centre line in the CENTRE of the strip.
4. Label a third strip “Secondary consumers”
Only 10% of the energy present in the biomass of the Primary consumers is transferred to the secondary consumers. Therefore the length
of this third strip must be 10% of the second one. Determine this amount, write it down in your table and cut the strip. Keep the centre
line in the CENTRE of the strip.
5. Determine how long the strip would be for Tertiary consumers, record this in your table, but do not cut a strip.
6. Arrange the three strips in a pyramid with the centre lines aligned in the middle of the pyramid. Glue them to your paper and label this diagram
“Energy Pyramid One”
This first pyramid is a generalized Energy pyramid to illustrate the method.
Now create two more specific pyramids.
TASK 2
One for a Temperate forest and
TASK 3
another for a Coniferous forest using the following information on page 3.
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Temperate & Coniferous Forests
A temperate forest, like the Eilenreide produces approximately 8,000 kilocalories per square meter per year
(written 8,000 kcal/m2/year = 33,600 kJ/m2/yr (1 calorie = 4.2 joules)).
It consists mainly of deciduous trees that lose there leaves each year.
A coniferous forest populated with trees that do not lose their leaves in the winter produces less biomass, only about 3,000 kcal/m2/year.
(How many Joules is that?)
1. Use the data table on the next page to calculate energy present in each level
2. Using a scale that 10 millimeters equals 400 kcal make an energy pyramid that represents the amount of energy captured by one square meter
of temperate deciduous forest in a year and another that represents the amount of energy captured in a year by one square meter of coniferous
forest.
3. First record the length of the strips that you need and the kilogram calories each represents in the correct place in the table. Calculate also the
amount of energy lost at each level.
4. Except for the scale, follow the steps 1-6 above. Tape or glue each completed energy pyramid to your paper and label it with the correct title.
Note: if some of the strips are too small to cut, use a pencil to draw that section of the pyramid.
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Pyramids of Energy
Pyramid One
Energy present
Length of strip (mm)
(kilocalories)
Energy lost as heat
(kiloalories)
Producers
240
240
Primary Consumers
24
24
Energy present (kcal)
Length of strip (mm)
Energy lost as heat (kcal)
Energy present (kcal)
Length of strip (mm)
Energy lost as heat (kical)
216.0
Secondary Consumers
Tertiary Consumers
Temperate Forest
Energy Pyramid
Producers
Primary Consumers
Secondary Consumers
Tertiary Consumers
Coniferous Forest
Energy Pyramid
Producers
Primary Consumers
Secondary Consumers
Tertiary Consumers
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TASK 4
Conclusion/Analysis (Use your own paper to answer these questions)
1. Explain what has happened to the energy that is not transferred at each feeding level.
2. Explain why the energy that is not transferred at each level can not be picked up by plants and cycled back though the system the way
molecules are cycled.
3. The first law of thermodynamics states that energy can neither be destroyed nor created. The second law of thermodynamics states that in
every energy conversion, some energy is lost as heat. Explain how these laws relate to the functioning of an ecosystem.
4. If 1000 kg of plant material are consumed by the rabbit population of an area explain why a few days later the rabbit population does not weigh
1000 kg more than it did.
Here is a typical pyramid:
Image from: http://kentsimmons.uwinnipeg.ca/16cm05/1116/16ecosys.htm
Incidence of solar power at surface, temperate, mid-day
~ 1000 Watts/m2
= 1000 Joules/second/ on each m2
~ 250 cal/sec
on each m2
~ 8,000,000 kcal/year
on each m2
1% of this is 80,000 kcal/yr/m2, so trees which produce 8,000 kcal/yr/m 2 are converting about 0.1% of the solar energy landing on that ground.
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Pyramid of Energy: Feeding Levels
This material is edited from open source material at: http://www.bbc.co.uk/schools/gcsebitesize/science/aqa/human/
http://en.wikipedia.org/wiki/Ecology, with reference also to: Science World Book 2, Stannard & Williamson.
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