1. The 10% Rule

2. All of the energy on Earth originally comes from the sun.
Producers, or plants, turn that radiant energy into chemical energy (glucose) that the plant can use during photosynthesis.
An energy pyramid’s shape shows the amount of useful energy that enters each level.

3. Each level in a food chain is called a trophic level.
The chemical energy, in the form of food, decreases as it is used by the organisms in that level.
Both plant and animal cells need energy to survive and grow.

4. They can break down glucose to release the chemical energy inside.
This process is called cellular respiration.
The problem is that even though a lot of energy may be taken in at any level, the energy that is stored and available to the next level is far less.

5. Scientists have calculated that an average of 90% of the energy entering each level is stored and stays at that level.
Only 10% of the energy is available to the next level.
For example, a plant will use 90% of the energy it gets from the sun for its own growth and reproduction.

6. When it is eaten by a consumer, only 10% of its energy will go to the animal that eats it.
That consumer will use 90% of that energy and only 10% will go on to the animal that eats it.
By the time you get to the top level, there is only a minor fraction of the original energy.

7. The tertiary consumers at the top of the energy pyramid will have much less available energy to support them than the primary and secondary consumers below them.
That’s why their population numbers are fewer in most food chains.

8. The amount of useful energy left eventually cannot support another level.
That’s why energy flow is shown in the shape of a pyramid and most chains are rarely longer than three or four trophic levels.

9. Label each level of the energy pyramid below as:
producer
primary consumer
secondary consumer
tertiary consumer.

11. 2. Cut out the grass, lion, hyena, sun and gazelle pictures and place them in the right place on the pyramid.

12. 3. If the sun is providing 6,000 calories of energy to the plant, calculate how many calories the organism at each level will receive.
Write that number in the box with the organism.

13. The sun is providing 6,000 joules of energy to the ecosystem in our example.
The grass only gets 10% of that energy.
How do we find 10% of a number?

14. When you need to find a percent of a number you multiply.
But you have to change 10% into a decimal first.
To do that, you move the decimal 2 spaces to the left.

15. 10%
.10
Now we can multiply 6,000 by .10

16. . 6000 .10 6 X Now we have to place the decimal.
So, the grass only gets to use 600 joules. Write this on your paper.

17. Energy going other places.
600 joules

18. Mass 600 grams of sand using the triple beam balance to represent the energy the grass is getting.
A gazelle comes along and eats some of the grass.

19. Does the gazelle get all 600 joules of the grass’s energy?
No. The grass uses 90% of the energy for daily functions like growing, healing, reproduction etc.

20. The gazelle will only get 10% of the 600 joules?
How do we figure out the number of calories the gazelle will get?
Remember, we multiply 600 by 10%.

21. . 600 .10 6 X Now we have to place the decimal.
So, the gazelle only gets to use 60 joules. Write this on your paper.

22. Energy the grass needed for life
60 joules

23. Mass 60 grams of sand using the triple beam balance to represent the energy the gazelle is getting.
A hyena comes along and eats the gazelle.

24. Does the hyena get all 60 joules of the gazelle’s energy?
No. The gazelle uses 90% of the energy for daily functions like growing, healing, reproduction etc.

25. The hyena will only get 10% of the 60 joules?
How do we figure out the number of calories the hyena will get?
Remember, we multiply 60 by 10%.

26. . 60 .10 6 X Now we have to place the decimal.
So, the hyena only gets to use 6 joules.

27. Energy the gazelle needed for life
6 joules

28. Mass 6 grams of sand using the triple beam balance to represent the energy the hyena is getting.
A lion comes along and eats the hyena.

29. Does the lion get all 6 joules of the hyena’s energy?
No. The hyena uses 90% of the energy for daily functions like growing, healing, reproduction etc.

30. The lion will only get 10% of the 6 joules?
How do we figure out the number of calories the lion will get?
Remember, we multiply 6 by 10%.

31. . 6 .10 6 X Now we have to place the decimal.
So, the lion only gets to use .6 joules.

32. Energy the hyena needed for life
.6 joules

33. Mass .6 grams of sand using the triple beam balance to represent the energy the lion is getting.
Record the .6 joules on your paper.

34. What is happening to the amount of available energy as you go from producer to tertiary consumer?
It is decreasing.

35. Is energy disappearing?
No. Energy cannot be created or destroyed but it can change into different forms of energy.
Energy can also be converted into matter.

36. The more energy you have at the producer level, the more organisms you can have in that ecosystem.

37. The less energy you have at the producer level, the fewer organisms you can have in that ecosystem.