AMNH Lesson Plan 8/10/00 A.

Lab Title: "SO WHAT’S WRONG WITH HEAVY METALS?"

Key Idea: #7 – Man’s impact on the earth

Major Understanding:

7.1c – Human activities can alter the equilibrium of ecosystems

7.2a – Pollution changes the chemical composition of air, soil, and water

Subject: Heavy metals as derivatives of human energy consumption entering biotic and abiotic systems

Discussion (Background): Assessing prior knowledge –

1. Discussion of meaning of "toxicity" (Is it a city in New York?). Write student definitions on board.
2. Discussion of the beneficial nature of most (89% of) bacteria are "good"
3. Discussion of safe handling of pigments (use gloves; wash hands and under nails thoroughly after handling).

Motivation: Students have a choice of "Coins" or "Colors" to test for toxicity

Get in groups of 3’s of same choice

Receive copy of chart (hand-out) on heavy metals to test

Guess (hypothesize) which metal (in coin or pigment form) you think will slow or prevent good bacterial growth. Write guess on chart.

CHART:

Experiment: Agar Diffusion Technique to examine metals as bacterial inhibitors

Prior Knowledge: Some understanding of agar plates and bacterial growth would be helpful.

Materials: Plastic gloves. Approximately 21 agar plates per class, with tops. E.coli bacteria, safe version. 7 glass "Elbows" (one per group; or, if limited time, teacher demonstrates the method of inoculation to class but this time supplies them with preinoculated plates. 9-10 coins (see chart). 9-10 tubes (or samples from tubes) of oil paint (see chart). 12 filter paper discs.

Method: Tape plate to board to hold still. Each group place 3 coins or 3 oil colors (in small dabs on paper discs) on inoculated plates. Each group record choice and arrangement. Carefully move board to undisturbed area to incubate at room temperature 24-48 hours (or longer, depending on your schedule).

After incubation time, observe and record results. A zone of inhibition is created when bacterial growth has stopped around a coin or pigment. If there is some regrowth of bacteria within this zone it is a sign of mutant bacterial colonies.

Conclusion: Students write conclusions based on observations.

Assessment: Lab Reports. Paragraphs done in class to explain results and predict (again hypothesize) damage to other organisms.

Follow-up: A way to distinguish whether the metal acts as a bacteriocide (killer) or bacteriostat (slower) would be an experiment attempting to grow bacteria from a sample taken from the zone of inhibition.

The specific mechanism creating a zone of inhibition can be described as oligodymanic activity interference with enzyme activity. AP or chemistry students may want to explore this process further. It can be included in a lesson on how enzymes work.

Resources: Meyer, Ralph (1970), The Artist’s Handbook of Materials and Techniques (3^rd edition). New York: Viking Press. (see "Toxicity)

Art supply store

Note: The teacher should test some coins and pigments on own first. The first 4 coins should show zones of inhibition. I have not tested oil paints but think results would be obtained without interference from the linseed oil medium. Only tests will tell. Lead white was the favored white pigment for 100’s of years for its superior opacity and was used by fine and commercial artists alike as well as house, boat, and car painters. It is now banned because of its extremely dangerous lead content and you can’t get it in any hardware store.