Bioassay Investigations
with Daphnia
Developed by Kathy Cahill
Wantagh High School
Wantagh, New York
Inquiry Process Skills
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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
100
All Affected
% Response
75
50
Half Affected
25
No Effect
0
0
10
20
30
40
50
60
70
80
Dose (mg/kg body weight)
90 100
LD50
Lethal Dose 50 is the concentration of a substance which
causes the death of 50% (one half) of a group of test
organisms.
% Response
100
All Affected
75
50
25
Half Affected
No Effect
0
0 10 20 30 40 50 60 70 80 90 100
Dose (mg/kg body weight)
Why Use LD50
Toxicant
Ethyl alcohol
Salt (sodium chloride)
Iron (Ferrous sulfate)
Morphine
Mothballs (paradichlorobenzene)
Aspirin
DDT
Cyanide
Nicotine
Black Widow Spider venom
Rattle Snake venom
Tetrodotoxin (from fish)
Dioxin (TCDD)
Botulinum Toxin
LD50 (mg/kg)
10,000
4,000
1,500
900
500
250
250
10
1
0.55
0.24
0.01
0.001
0.00001
Bioassay Investigations
with Daphnia
Part 1
Part 2
Introduction to
Bioassays
Investigating the Effects of
a Toxicant on Daphnia
Guided
Version
Inquiry
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.
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.