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By Susan E. Emerson


  • Hands-on laboratory activities
  • Simulation of a town hall meeting
  • Inquiry discussion
  • Group/cooperative learning
  • Community connections


  • Life Science
  • Biology
  • Advanced/AP Biology
  • Integrated Science
  • Environmental Studies
  • Chemistry classes


This lesson is designed to appeal to students with a variety of learning styles and abilities. Students feel successful since they can all gather data in the lab and participate in class discussion and work cooperatively in the Town Hall meeting. Analysis and application questions and tasks are open-ended to elicit different levels of response depending upon student ability and background.


Notes For the Teacher:

I save this lesson for a time during the school year when something similar is in the news. One of the most appealing attributes of children is their sense of wonder for the world around them. As educators, we need to take advantage of this natural curiosity. This lesson is successful because it includes the nurturing of that curiosity and empowering students at all levels to find and process relevant information. Parts per million and LD-50's become relevant, important pieces of information in student's lives. Most gratifying to me is the personal involvement and interest generated by my students.

Required of Students:

  • Students must research information about pesticides, LD-50s etc. to prepare for their role in the Town Hall Meeting.
  • Students must practice their role and come up with an appropriate costume.

Preparation Time Needed:

Very little preparation time is needed. Background information needs to be gathered and equipment must be set out for the serial dilution lab. Since food coloring is utilized, no mixing of chemicals is required.

Class Time Needed: This lesson can be modified to three days or extended as desired.



A favorite activity for my students is an environmental study of the effects of spraying malathion on Mexican fruit flies. In 1990, the city of El Cajon experienced an infestation of Mexican fruit flies, necessitating an aerial spraying of the insecticide malathion. The local community had a very emotional response to the procedure; community meetings were held, demonstrations launched, and in many cases students stayed home from school after the spraying. In response to overwhelming interest, a colleague and I collaborated to create a series of lessons about the Mexican fruit fly, the insecticide malathion and risk assessment. It was an opportunity to do cross disciplinary teaching, enabling students to see interrelationships between biology, chemistry and local government. The lesson includes background reading for discussion on the Mexican fruit fly, insecticides, and LD-50s. Students complete a short lab on serial dilutions, with risk analysis application problems and a Town Hall meeting to decide if the spraying should take place or develop alternatives.

Materials Needed:

  • Food coloring
  • Dropper
  • One well plate per team
  • Water

Description of Activity:

  • Part 1
    Class discussion and direct instruction on the natural history of the Mexican fruit fly and the insecticide malathion. An inquiry approach is utilized to discuss and analyze risk assessment using concentrations and LD-50s.

  • Part 2
    Students complete a serial dilution laboratory using food coloring, droppers and well plates to learn about concentration levels in ppt, ppm, ppb etc. Application questions in this lab relate to malathion concentration levels in the bottle, the air, bodies of water and in organisms. Students relate this to trophic levels and concentration of some toxins at the top of the food chain. Using LD - 50 data students do a risk analysis and make comparisons to toxicity of some household products.

    Questions include:

    1. A male pheasant flew through the contaminated air in pursuit of his mate. Ten percent of the malathion was absorbed into his bloodstream. Was this a fatal attraction? Explain your reasoning.

    2. Homer Simpson attempted to rid his yard of ants and fleas by spraying with malathion. Oblivious to hazardous waste regulations, he dumped the remaining poison in his trash can. The poison saturated the leftover Big Mac from Bart's lunch. Later that night, Rocky the roof rat ate the remains of the Big Mac. The Big Mac leftovers weighed 0.10 lb, Homer dumped 1.5 g malathion and Rock was an average size rat. Did Homer kill Rocky along with the ants and the fleas? Show your work.

  • Part 3
    Students work cooperatively to simulate a Town Hall meeting. Students are assigned roles including the Mayor, City Council members, an orange grove farmer, agricultural inspectors, local residents including some with small children and backyard fruit trees, and a local koi fish breeder with an outdoor pond, a chemist, a biologist, the Governor, a teacher, and reporters. Students research their positions and role play the activity. Students must submit a position paper. The entire class enacts the meeting. It may be video taped and students should dress for their part. (An alternative is to assign fewer roles and have students complete the activity in smaller cooperative groups.)


Evaluation is based upon lab reports and town hall meeting presentation.


Extension activities include lessons on solubility, library research, analysis of related news articles for fact and fiction and constructivist lab activities on pollution (i.e. acid rain).

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