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Bioassay Investigations with Daphnia Developed by Kathy Cahill Wantagh High School Wantagh, New York.

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Presentation on theme: "Bioassay Investigations with Daphnia Developed by Kathy Cahill Wantagh High School Wantagh, New York."— Presentation transcript:

1 Bioassay Investigations with Daphnia Developed by Kathy Cahill Wantagh High School Wantagh, New York

2 Inquiry Process Skills Hypothesizing Preparing solutions Designing and conducting experiments Recording experimental data Analyzing experimental data Drawing conclusions Considering further research

3 Environmental Science Concepts Use bioassay to develop students’ understanding of: –The effect of toxicant concentration on organisms –The use of model organisms as indicators of potential health hazards for humans

4 Chemical Risk? What is the chance that human health problems will result from exposure to a particular toxicant? Is it safe to eat fruits or vegetables containing traces of pesticide residues? Should fluoride be added to drinking water? Is diet soda safe to drink?

5 Toxicant A chemical or mixture of chemicals that is harmful to living organisms. It’s the dose (concentration) that makes the poison.

6 Identifying Risks To identify possible risks from exposure to a particular toxicant, scientists use simple plants or animals, rather than humans, as test subjects.

7 Bioassay A procedure that uses living organisms to determine the toxicity of a chemical. 1. Expose living organisms to different concentrations of a potential toxicant 2. Observe the effects on the organisms’ behavior and survival 3. Determine if, or at what concentration, a chemical has harmful effects

8 Model Organisms Why use model organisms? What other kinds of organisms might be used for bioassays?

9 Dose-Response Curve Dose (mg/kg body weight) No Effect All Affected Half Affected % Response

10 LD 50 L ethal D ose 50 is the concentration of a substance which causes the death of 50% (one half) of a group of test organisms. Dose (mg/kg body weight) No Effect All Affected Half Affected % Response

11 Why Use LD 50 ToxicantLD50 (mg/kg) Ethyl alcohol10,000 Salt (sodium chloride)4,000 Iron (Ferrous sulfate)1,500 Morphine 900 Mothballs (paradichlorobenzene) 500 Aspirin250 DDT250 Cyanide10 Nicotine1 Black Widow Spider venom0.55 Rattle Snake venom0.24 Tetrodotoxin (from fish)0.01 Dioxin (TCDD)0.001 Botulinum Toxin

12 Bioassay Investigations with Daphnia Part 1 Introduction to Bioassays Part 2 Investigating the Effects of a Toxicant on Daphnia Inquiry Version Guided Version

13 Timeline Part 1: Introduction to Bioassays Two 40 minute class periods –Introduce –Do procedure and make observations (absolute minimum of 40 minutes and may need to adjust observation time) –Analyze data and answer questions

14 Introduction to Bioassays Materials for each pair of “students” Jar containing living Daphnia Plastic exposure chamber (or 6 test tubes or small cups) One large plastic pipette Two small plastic pipettes (note 1 mL marking near the top) 10 mL Graduated cylinder 6 small beakers or cups for mixing solutions Spring water (0% salt) Salt solutions (0.2 – 2%)

15 Introduction to Bioassays Complete through step 4. Do not add the solutions to the exposure chambers until instructed to do so.

16 Introduction to Bioassays Complete steps 5 and 6 Your teacher will notify you when to make the 5, 10, and 20 minute observations.

17 Introduction to Bioassays Work with your partner to complete the: – Data table – Graph – Data analysis and Interpretation questions

18 Investigating the Effects of Toxicants on Daphnia Two versions: Guided Version or Inquiry Version Select ONE of these

19 Guided Version Investigating the Effects of Toxicants on Daphnia Similar to the first experiment but students will: –Investigate other toxicants –Construct their own data table and graph –Discuss application to humans –Share and draw conclusions based on information from other groups

20 Guided Version Timeline Two 40 minute class periods –Introduce –Do procedure and make observations (absolute minimum of 40 minutes and may need to adjust observation time) –Analyze data and answer questions

21 Inquiry Version Students apply their understandings from the introductory laboratory activity by: Designing an experiment to investigate the effects of other toxicants. Constructing their own data table and graph Drawing conclusions and discuss application their applications to humans Optional: Sharing and drawing additional conclusions based on information from other groups

22 Inquiry Version Timeline One period for designing procedure At least one period for conducting experiment One period for analyzing group data Optional additional period for class sharing and discussion of results.

23 Work with three others Select a toxicant Design an experiment to investigate the effect of the toxicant on Daphnia Complete the exposure chamber graphic and the experiment planning sheet for your proposed experiment. Record your work on the transparencies so that you are prepared to share your plan with others.

24 Extensions/Modifications Talk with others at your table and make a list of ways that these experiments could be extended or modified. Record your work on the transparency to that you are prepared to share your plan with others.


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