1. Unit A: Energy and Matter Exchange in the Biosphere
Chapter 2
Section 2.2
Scientific Models

2. Ecological Pyramids
An ecological pyramid is a representation of the energy flow in a food chain or a food web.
There are three types of ecological pyramids:
Pyramids of Numbers
Pyramids of Biomass
Pyramids of Energy

3. Pyramids of Numbers
A pyramid of numbers can be drawn by counting the number of organisms at each trophic level in an ecosystem.
When these numbers are represented in a visual graph they often take the shape of pyramids because the number of organisms decreases with each trophic level.

4. Pyramids of Numbers

5. Pyramids of Biomass
Biomass is the total dry mass of all the living material in an ecosystem.
Since organisms store energy as organic molecules, biomass is a measure of stored energy content.
A pyramid of biomass represents the total biomass at each trophic level per 1m2.

6. Pyramid of Biomass

7. Primary Consumers = 1 x 109 kJ Secondary Consumers = 1 x 108 kJ
Pyramids of Energy
Pyramids of energy are a representation of the amount of energy available at each trophic level.
The energy available decreases with each level because only 10% of the energy at each step is passed on.
Producers = 1 x 1010 kJ
Primary Consumers = 1 x 109 kJ
Secondary Consumers = 1 x 108 kJ

8. Pyramids of Energy

9. Sample Question #1
Pg. 30 in textbook

10. Practice Question #1 Trophic Level Number of Organisms
Area of Box (cm²)
≈ Length of 1 Side (cm) 1
100 10
3.2 2
9800 3
500 4 5

12. Sample Question #2
Pg. 32 in textbook

13. Practice Question #2 Organism Energy (kJ) Area of Box (cm²)
≈ Length of 1 Side (cm)
Phytoplankton
200
14.1
Zooplankton
Herring
Salmon

14. Practice Question #3
Pg. 32 in textbook