1. Energy Ineffiency Trophic level = step in a food chain
Key Point #1: Only 10% of the energy in a food web is passed from one trophic level to the next. The rest is given off as heat/used in daily activities.
- Called the “10% rule.”
The higher up in the food chain you go, the more food an organism must eat to get the same amount of energy. 1%
0. 1% 1%
This is why there are usually only a few trophic levels in a food chain.
My students in the past have had a LOT of trouble with the 10% rule. Good luck!
10%
10%
100%

2. Who has the most energy in this food web?

3. Who has the least energy in this food web?

4. Does the cougar get more energy when it eats a fox or when it eats mice?

5. Let’s practice math What is 10% of Answers 100 10 2000 200 452 45.2
348.7
27.22
Answers 10
200
45.2
34.87
2.722

6. Example
The ranches of the American Midwest are full of grass. The grass uses sunlight to grow. Cows and rabbits graze on the grass. However, the grass provides these animals little shelter from wolves, which eat the cows and rabbits.
A – The sun provides energy for producers. Primary and secondary consumers eat producers. Without energy from the Sun, the ecosystem could not function.
B – All energy that enters the food web begins with the Sun. The grass receives 100% of the Sun’s energy. The wolves receive 1%.

7. Example 1
Wolves: 10kcal
Cows and Rabbits: 100kcal
Grass: 1000kcal

8. Example 2
Wolves: 34.5kcal
Cows and Rabbits: 345kcal
Grass: 3450kcal

9. End of class I need: Partner packet Ls quiz In your folder Daily Quiz
Independent Practice (if you got to it)