ms. molstad east high school chemistry in the community class
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Ms. MolstadEast High School
Chemistry in the Community Class
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Pre-TestDetermining Prior Knowledge
Assess what you learn during lab
10 PointsDo the best you can
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What is a Bioassay?Involves use of a
biological organism to test for chemical toxicityEx: Canary in the coal
mineTest effects of
compound being considered for use in drugs
Environmental testing
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Dose/Response ExperimentExpose organisms to
various levels of a chemical and then measure their response
Duckweed is the bioassay organism
Place duckweed in various concen. of chemical, you monitor growth and health over a period of 7 days.
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What is Duckweed?Small aquatic plant Found on surface of
ponds, wetlands, and nutrient rich lakes.
Lemna minor Food source for
some animalsFast growing
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Is Duckweed Bad for Waterways?Increased nutrients =
Increased duckweed
Lake Eutrophication: Increased P & N Causes algal bloomsReduced dissolved OKills other organisms
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Where do the Increased Nutrients Come From?Human activity
at homeAgricultural
runoffGolf coursesUntreated
sewageIndustrial runoff
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Duckweed Bioassay LabTest the affect of
various concentrations of fertilizer on an aquatic plant
PredictHypothesisConduct ExperimentAnalyze resultsForm Conclusion
Duckweed Bioassay Data
Solution Concentration
# Duckwee
d Fronds/C
up
Avg. #
Fronds
Comments about Plant
Health
Control
Fertilizer Concentration ( %)
Fertilizer Concentration ( %)
Fertilizer Concentration ( %)
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Duckweed ReproductionBy budding-new
fronds grow from buds on parent plant
Measure growth rate by counting how many new fronds develop
Frond Counting
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Lab ProceduresLab Set Up/Participation Data Collection &
AnalysisLab ParticipationSet Up
Filling in tableGraphQuestions
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Last Day of Counting!Duckweed Frond Counts-Class Averages
Day 1 Day 3 Day 5 Day 8
Control
100%
10%
1%
0.10%
0.01%
0.001%
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Question #4 TC50TC50The Toxic
Concentration that kills 50% of Duckweed
ORThe Toxic
Concentration that causes Duckweed to grow ½ as well as those in the control group
1. Look at ControlDay 1 – 20 frondsDay 8- ___ fronds
2. Look at Day 8Which soln. had ½ as many fronds as the control?If no ½, then list a range
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Determining Doubling TimeQuestion #6 in
PacketShould have 3 soln.
conc. to determine doubling time for.
Some might show negative growth
To Calculate Duckweed Growth Rate:
n = the number of days over which growth is measuredFo = the number of fronds at day 0Fn = the number of fronds at day nD = the doubling time of duckweed (in days)D = {(nlog2) divided by (logFn - logFo)} days
Ex: If at day 0 there are 8 fronds and at day 4 there are 18 fronds, thenD = {(4 x log2) divided by (log18 - log 8)}= {(4 x 0.301) divided by (1.255 - 0.903)}= 3.4 days
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Why Use a Bioassay?Use of a biological
organism to test for chemical toxicity
Examples of use:Test effects of
compound being considered for use in drugs
Environmental testing
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Tuesday:Turn in Lab PacketPost Test