1. Ms. Molstad East High School Chemistry in the Community Class
Duckweed Bioassay
Ms. Molstad
East High School
Chemistry in the Community Class

2. Pre-Test Determining Prior Knowledge Assess what you learn during lab
10 Points
Do the best you can

3. What is a Bioassay?
Involves use of a biological organism to test for chemical toxicity
Ex: Canary in the coal mine
Test effects of compound being considered for use in drugs
Environmental testing

4. Dose/Response Experiment
Expose 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.

5. What is Duckweed? Small aquatic plant
Found on surface of ponds, wetlands, and nutrient rich lakes.
Lemna minor
Food source for some animals
Fast growing

6. Is Duckweed Bad for Waterways?
Increased nutrients = Increased duckweed Lake Eutrophication: Increased P & N Causes algal blooms Reduced dissolved O Kills other organisms

7. Where do the Increased Nutrients Come From?
Human activity at home
Agricultural runoff
Golf courses
Untreated sewage
Industrial runoff

8. Duckweed Bioassay Lab
Test the affect of various concentrations of fertilizer on an aquatic plant
Predict
Hypothesis
Conduct Experiment
Analyze results
Form Conclusion
Duckweed Bioassay Data
Solution Concentration
# Duckweed Fronds/Cup
Avg. # Fronds
Comments about Plant Health
Control
Fertilizer Concentration ( %)

9. Duckweed Reproduction
By budding-new fronds grow from buds on parent plant
Measure growth rate by counting how many new fronds develop
Frond Counting

10. Lab Procedures Lab Set Up/Participation Data Collection & Analysis
Lab Participation
Set Up
Filling in table
Graph
Questions

11. Happy Counting!

12. Last Day of Counting! Duckweed Frond Counts-Class Averages Control
100%
10% 1%
0.10%
0.01%
0.001%

14. Add in your graph with final Duckweed counts

15. Question #4 TC50 TC50 1. Look at Control
The Toxic Concentration that kills 50% of Duckweed OR
The Toxic Concentration that causes Duckweed to grow ½ as well as those in the control group
1. Look at Control
Day 1 – 20 fronds
Day 8- ___ fronds
2. Look at Day 8
Which soln. had ½ as many fronds as the control?
If no ½, then list a range

16. Determining Doubling Time
Question #6 in Packet
Should 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 measured Fo = the number of fronds at day 0 Fn = the number of fronds at day n D = 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, then D = {(4 x log2) divided by (log18 - log 8)} = {(4 x 0.301) divided by ( )} = 3.4 days

17. 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

18. Tuesday:
Turn in Lab Packet
Post Test