Ms. MolstadEast High School

Chemistry in the Community Class

Pre-TestDetermining Prior Knowledge

Assess what you learn during lab

10 PointsDo the best you can

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

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.

What is Duckweed?Small aquatic plant Found on surface of

ponds, wetlands, and nutrient rich lakes.

Lemna minor Food source for

some animalsFast growing

Is Duckweed Bad for Waterways?Increased nutrients =

Increased duckweed

Lake Eutrophication: Increased P & N Causes algal bloomsReduced dissolved OKills other organisms

Where do the Increased Nutrients Come From?Human activity

at homeAgricultural

runoffGolf coursesUntreated

sewageIndustrial runoff

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 ( %)

Duckweed ReproductionBy budding-new

fronds grow from buds on parent plant

Measure growth rate by counting how many new fronds develop

Frond Counting

Lab ProceduresLab Set Up/Participation Data Collection &

AnalysisLab ParticipationSet Up

Filling in tableGraphQuestions

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%

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

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

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

Tuesday:Turn in Lab PacketPost Test