A food chain is a model that shows how energy is passed, in the form of food, from one organism to another. The arrows between the organisms show the direction of energy flow.
The organisms in a food chain can be either producers, consumers,
or decomposers.
Producers are green plants capable of making their own food using
energy from the sun in a process called photosynthesis.
Consumers are animals that cannot make their own food. They get their energy from other plants and animals. A food chain can have as many as three to four consumers.
First level consumers feed directly on plants; an
example of this would be a mouse.
Second level consumers feed on first level consumers;
an example of this would be a rattlesnake that eats the mouse. Third
level consumers feed on second level consumers; an example
of this would be a hawk eating the rattlesnake. 
Decomposers
are also unable to make their own food. Bacteria and fungi are decomposers.
They break down waste products and dead organisms for food. These broken
down materials are returned to the soil to be recycled and used by plants
again. An example of this would be a fungus growing on a log. Although
decomposers are very important to ecosystems, they are usually not shown
on the food chain. Look at the following list of organisms and identify
them as either producers, consumers, or decomposers.
| Organisms | Role in food chain |
| Human | |
| Deer | |
| Pine tree | |
| Bear | |
| Rabbit | |
| Bacteria | |
| Mouse | |
| Snake | |
| Wheat | |
| Fly maggot | |
| Bluegrass | |
| Hawk | |
| Millipede | |
| Sparrow | |
| Cat | |
| Frog | |
| Algae | |
| Trout | |
Test
your knowledge of food chains by drawing some of your own. Draw and
color 3 food chains with four organisms in each. Make your food chains for
diverse ecosystems ... the desert, the forest, the plains of Africa, the
ocean, the arctic. Be creative. Be sure to include arrows to show the direction
of energy flow. Label each member of the food chain as the producer; or
first, second, or third level consumer.
Use
the scientific method and explore the process a wildlife biologist uses
to determine when
the hunter killed a cougar. 
