BioEd Online

Teacher Background

Many pollutants in the environment become introduced in very small amounts into organisms near the base of the food chain. These pollutants usually are present in the water or the soil in which producers, such as green plants and algae, or primary consumers, such as filter feeders in aquatic ecosystems, live and reproduce. Pesticides that are applied directly to plants can also be introduced into the food chain.

Some chemical substances, such as pesticides and heavy metals (like mercury and lead), persist within the bodies of the organisms that take them in with food. These compounds are not broken down by the body, nor are they eliminated with other waste products. While most of these substances are not harmful in trace amounts, they can accumulate in the tissues of an organism over its lifetime. In addition, consumers near the top of the food chain tend to accumulate larger amounts of toxic substances in their bodies, because the pollutants become more concentrated at each step of the food chain. The actual amounts of toxins accumulated in the bodies of top consumers depend on their food sources and choices.

Objectives and Standards

Concepts

• Pollutants often are absorbed by organisms near the base of a food chain.

• Toxic chemicals can become concentrated in the bodies of consumers, especially those near the top of the food chain.

Science, Health, and Math Skills

• Counting

• Multiplying

• Observing patterns

• Drawing conclusions

Materials and Setup

Materials per Student

• 80 (approx.) 1/4-in. round color coding labels (dots), asst. colors

• crayons or colored markers

• pair of scissors

• copy of "Bio Build-up!" sheet

Setup

1. As an alternative, glue and dried beans or unpopped popcorn can be substituted for the adhesive labels/dots.

2. Have students work in groups of 2–4 to share materials.

Procedure and Extensions

1. Let the Materials Managers collect adhesive dots (or alternative items) for their group (approx. 80 dots per student). Each student should complete his or her own "Bio Build-up!" sheet.

2. Prompt students to think about what might happen to pollutants taken up by producers. Ask, Would the pollutants be passed on to consumers? How about the next animal in the food chain? Would they have the pollutants too? Tell the students that they will have an opportunity to find out what might happen to pollutants in a food chain.

3. Have students use a pair of scissors to separate 20 dots from the strip (or sheet) without removing the backing. Next, have them work through the steps described on the "Bio Build-up!" sheet, which depicts an aquatic ecosystem. The stickers or other markers will represent amounts of toxins consumed along each step of the food chain.

4. Once students have completed the activity, ask, What happened to the pollutants at the last step of the food chain? Did the large fish have more or less pollutants than the plants at the beginning of the food chain? Did the amounts of pollutants in the plants at the beginning make a difference in the small and large fish? How could the amount of pollutants in the body of the eagle be reduced? In general, which kinds of organisms are most at risk of accumulating toxins in their bodies—producers or consumers? Students will have observed that the eagle accumulated the most pollution dots.

Handouts and Downloads