Energy Flow in Ecosystems

Ecologists study how energy moves through an ecosystem by assigning organisms in that ecosystem to a specific level, called a trophic level, based on the organism’s source of energy.

Energy moves from one trophic level to another. The path of energy through the trophic levels is called a food chain. The lowest trophic level is is occupied by the producers, which use energy from the sun to build carbohydrates.

At the second trophic level are herbivores, animals that eat plants and other types of producers. An herbivore msut be able to break down a plant’s molecules into usable compounds. Plants have a tough layer of cellulose, which only a few herbivores are capable of breaking down. Most herbivores rely on mircoorganisms, such as bacteria, in their gut to help them digest cellulose (humans do not have this in their system).

The third trophic level are secondary consumers called carnivores, animals that eat herbivores. Animals that are both herbivores and carnivores, such as bears, are called omnivores. They use simple sugars found in plants, but cannot digest the cellulose.

1. Label one producer, one consumer and one decomposer on the food chain above.

2. Write a food chain in which the hawk is a secondary consumer:

3. Write a food chain in which the hawk is a tertiary (3^rd) consumer:

4. Which trophic level is NOT shown in the food web above?

5. Which organism is gaining the most energy in this pyramid? ________________

6. Which organism is gaining the least energy in this pyramid? ________________

7. How much energy is available to the snake? ___________________________

8. Approximately how much energy is available to the secondary consumers in this energy pyramid?

A. 10 kcal/m2/year

B. 100 kcal/m2/year *

C. 1,000 kcal/m2/year

D. 5,000 kcal/m2/year

For numbers 1-8, write “1” if the clue describes the first trophic level, “2” if it describes the second trophic level, and “3” if the clue describes the third trophic level.

_____1. Primary consumers are found here.

_____2. Organism here use energy from the sun to build energy-rich carbohydrates.

_____3. Tigers, wolves, and snakes would be found here.

_____4. Organisms here are capable of breaking down cellulose.

_____ 5. Secondary consumers are found here.

_____ 6. Plants, algae, and bacteria are found here.

_____ 7. Humans would be found at this level.

______8. Organisms here rbeak down a plants into usable compounds.

______ 9. Which of the following is NOT an example of a primary consumer?

A. Maple trees

B. Caterpillars

C. Cows

D. horses

10. How are carnivores and omnivores alike? How are they different?