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Inquiry Process Skills
• Hypothesizing
• Preparing solutions
• Designing and conducting experiments
• Recording experimental data
• Analyzing experimental data
• Drawing conclusions
• Considering further research
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
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?
Toxicant
• A chemical or mixture of chemicals that is harmful to living organisms.
• It’s the dose (concentration) that makes the poison.
Identifying Risks
To identify possible risks from exposure to a particular toxicant, scientists use simple plants or animals, rather than humans, as test subjects.
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
Model Organisms
• Why use model organisms?
• What other kinds of organisms might be used for bioassays?
Dose-Response Curve
Dose (mg/kg body weight)
0
25
50
75
100
0 10 20 30 40 50 60 70 80 90 100
No Effect
All Affected
Half Affected
% R
es
po
ns
e
LD50
Lethal Dose 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)
0
25
50
75
100
0 10 20 30 40 50 60 70 80 90 100
No Effect
All Affected
Half Affected
% R
es
po
ns
e
Why Use LD50
Toxicant LD50 (mg/kg)Ethyl alcohol 10,000Salt (sodium chloride) 4,000Iron (Ferrous sulfate) 1,500Morphine 900Mothballs (paradichlorobenzene) 500Aspirin 250DDT 250Cyanide 10Nicotine 1Black Widow Spider venom 0.55Rattle Snake venom 0.24Tetrodotoxin (from fish) 0.01Dioxin (TCDD) 0.001Botulinum Toxin 0.00001
Bioassay Investigations with Daphnia
Part 1
Introduction to Bioassays
Part 2
Investigating the Effects of a Toxicant on Daphnia
Inquiry
Version
Guided
Version
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
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%)
Introduction to Bioassays
Complete through step 4.
Do not add the solutions to the exposure chambers until instructed to do so.
Introduction to Bioassays
Complete steps 5 and 6
Your teacher will notify you when to make the 5, 10, and 20 minute observations.
Introduction to Bioassays
Work with your partner to complete the:
– Data table– Graph– Data analysis and Interpretation
questions
Investigating the Effects of Toxicants on Daphnia
Two versions:
Guided Version or Inquiry Version
Select ONE of these
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
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
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
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.
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.
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