Lesson Plan Industry Sector
Agriculture & Natural Resources

Lesson Plan Originally Created By: Beth Knapp

Accumulation of Toxins in Food Web -- Beth Knapp

Part of Unit: Ecology

Lesson Plan Overview / Details

This activity will take students through the process of bioaccumulation of toxins in the food web. Students will model how energy is transferred through the aquatic food chain and how toxic material can enter the food chain.

Lesson Time

Instructional Time
50 Minutes

Objectives and Goals

  • Students will be able to model energy transfer through the aquatic food chain.
  • Students will be able to explain how a toxic material can enter the food chain.
  • Students will be able to analyze the affects of biological magnification and bioaccumulation.

Teacher Prep

  • Weaving the Web Opening Activity- Ball of Yarn and printed organism pcitures for each student.
  • Accumulation of Toxins in the Food Web- Plastic sandwich bags, pre-printed cards (20-daphnia, 7-mayfly larvae, and 3 small mouth bass), large bag of M&Ms.

Activities in this Lesson

  • As each student enters the classroom, they will received a picture cut-out of an organism. Each student will be assigned a different organism. For the purpose of this activity the teacher will be the sun. Once each student has been assigned an organism, take the students outside or clear the classroom so that students can arrange themselves in a large circle. Have each student introduce themselves as type of organism they have been assigned to. The teacher will stand in the center of the circle as they are representing the sun. Instruct the students to start thinking about who in the circle could I give my energy to (who might eat me?) and who in the circle could give me energy (whom could I eat?) as the introductions are occurring. The teacher will start the activity, and ask who gets energy from the sun? The teacher will pass a ball of yarn to the student who speaks up, stating their organism gets energy from the sun. The teacher will hold on to the end of the yarn as the ball is passed to the first student. The first students will then asked the class, "who can get energy from eating me?" Holding on to the yarn, they will then pass the ball of yarn to the student who consumes them. This activity will continue, until the top of the food chain is reached, each student hanging onto a piece of the yarn as the ball is passed. The yarn will go back to the teacher (sun) and the activity will continue until all students are weaved into the web.

    Resources and Materials

    • Weaving the Web Sample Directions and organism picture cut-outs [ Download ]
    • PowerPoint Example Food Web [ Download ] During this activity, you can use this powerpoint to show the students a visual of what they will be modeling.
  • Water quality problems have plagued California since the days of its early settlers. Our state’s massive water transportation and storage systems are testimony to the fact that California’s water supplies quite often do not occur where and when they are needed most. Our water supply is sometimes a case of glut of famine, flood or drought. But all the water in the world – in the right place at the right time – won’t do a drop of good if it isn’t fit to use!! True, our domestic water supplies have come a long way since the days when a glass of water might carry with it the threat of cholera or typhoid. But almost daily, the news media carry alarming stories of toxic substances threatening our ground water supplies. ** This would be a good time to talk about the connection between water and agriculture. A discussion regarding the Delta, farmers and the aquatic impact.

  • Vocabulary Lecture

    There are two basic terms we are discussing here. Bioaccumulation refers to how pollutants enter a food chain; biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next. Here are some definitions of these terms: Bioaccumulation:increase in concentration of a pollutant from the environment to the first organism in a food chain. Biomagnification:increase in concentration of a pollutant from one link in a food chain to another

    Resources and Materials

    • Bioaccumulation.html [ Go to Site ] Teacher Resource Website
    • 2bioma95.html [ Go to Site ] Teacher Resource Website
  • Clear all desks to the sides of the classroom. Place a table in the middle of the cleared classroom, open a bag of M & M's and spread them out on this table. Have students line up around the edges of the classroom. Students do not need anything with them; they can leave their lab sheets at their desks. Once students are in place, begin explaining the procedures of the Toxins in the Food Web activity (see Toxins in the Food Web attachment). Explain and define the food aquatic food chain to the students. For this activity the food chain will be water daphnia --> Mayfly larvae --> Small mouth bass. Pass out pre-printed strips of paper to students. Based on a class size of 30 students- 20 students will be water daphnia (a small fresh water animal), 7 students will be Mayfly larvae who will be preying on the daphnia, and lastly only 3 students will be assigned the small mouth bass who prey on the mayfly larvae.

    Each "daphnia" will receive a small plastic bag. The bag represents the food container to hold food energy. In other words, it is that organism stomach!!! Explain to the students the boundaries of the pond in your classroom that you will be using for this activity. Explain to students that the "food energy" will be represented by M&Ms scattered on the table.

    At this time, I would check for understanding by asking the students, to repeat the order of the food chain and to restate the boundaries of the pond to make sure the students were listening to the instructions so far. The first set of students that will start this activity is the "daphnia", who will be instructed to gather the "food" and place the M&Ms in their stomach(plastic bag). For this activity to work properly the daphnia will only be allowed to place the M&Ms in their bag one at a time. Explain that the daphnia will only have 30 seconds for their feeding. Using a stop watch to time, release the daphnia students into the pond for the allotted time. Call time after 30 seconds and have the daphnia remain inside the pond boundaries. Instruct the Mayfly larvae to prey on the daphnia by tagging them and collecting their stomachs. The eaten daphnia will then move to the sidelines. The Mayfly larvae will have 20 seconds to eat(tag) as many daphnias as possible. Allow the Mayfly larvae to feed on the daphnia for 20 seconds.

    After time is called, have all surviving daphnias and Mayfly larvae remain in the pond boundaries. Instruct to the small mouth bass that they will have 10 seconds to prey on the Mayfly larvae by tagging them and taking their stomachs (bags). After time is called, return the classroom to its original arrangement. The aquatic organisms that are still live are to empty their stomachs and separate the colors of M&Ms. At this time you will announce to the class that there is a toxic chemical loose in the water environment. Tell them it is poisonous and accumulates in the food chain and stays in the environment for a long time!! Pick a color of M&Ms and announce to the students that the ____________ M&Ms represent the poison. Have the students calculate the number of toxic M&Ms and the number of "safe" M&Ms in their food supply. Any of the Daphnia that were not eaten may now be considered dead if they have any of the toxic M&Ms in their food supply. Any mayfly larvae with a food supply that exceeds 40% of toxic M&Ms will also be considered dead. Any small mouth bass with a concentration of 50% or over of toxic M&Ms may be able to survive, but its ability to ward off disease, produce offspring and find or catch food may be limited.

    Resources and Materials

    • Accumulation of Toxins in a Food Web- Lab Sheet [ Download ] Students Lab Sheet including: Materials, Procedures, Data, Results, Analysis and Conclusion Questions.
  • As a class, select one living daphnia, one mayfly larvae and one small mouth bass to report their numbers to the class. Record together, the total M&Ms, number of safe M&Ms, number of toxic M&Ms and percent of toxic food supply for each organism. Refer to Accumulation of Toxins in a Food Web- Lab Sheet to see "Data & Results" section

  • After students have finished the Data and Results table, instruct students to complete the analysis and conclusion section. Refer to Accumulation of Toxins in a Food Web- Lab Sheet to see "Analysis & Conclusion" section


Assessment for student understanding and comprehension can be done by reviewing the analysis and conclusions questions. At the end of the lesson, I would use random calling to call on students to read and explain their answers for each question. I will be able to measure the students' command of the content based on the student responses to the seven analysis and conclusion questions.