Ms. Molstad East High School Chemistry in the Community Class Duckweed Bioassay Ms. Molstad East High School Chemistry in the Community Class
Pre-Test Determining Prior Knowledge Assess what you learn during lab 10 Points Do the best you can
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
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.
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
Is Duckweed Bad for Waterways? Increased nutrients = Increased duckweed Lake Eutrophication: Increased P & N Causes algal blooms Reduced dissolved O Kills other organisms
Where do the Increased Nutrients Come From? Human activity at home Agricultural runoff Golf courses Untreated sewage Industrial runoff
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 ( %)
Duckweed Reproduction By budding-new fronds grow from buds on parent plant Measure growth rate by counting how many new fronds develop Frond Counting
Lab Procedures Lab Set Up/Participation Data Collection & Analysis Lab Participation Set Up Filling in table Graph Questions
Happy Counting!
Last Day of Counting! Duckweed Frond Counts-Class Averages Control 100% 10% 1% 0.10% 0.01% 0.001%
Add in your graph with final Duckweed counts
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
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 (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 Packet Post Test