Duckweed Bioassay
Summary
This lab was designed with the intent to mimic the effect fertilizers can have on plants in a lake or pond ecosystem. Students determined the effect different fertilizer concentrations had on the growth rate of Duckweed plants compared to a control by counting fronds over a period of 8 days. A lab procedure and data sheet are provided.
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Learning Goals
Bioassays provide chemistry students with a hands-on lab technique to better understand and investigate a local environmental toxicity issue. Students are able to determine the effect different levels of fertilizer can have on a local aquatic system, learn new research and analysis techniques to determine the growth rate and chemical toxicity levels fertilizers have on an aquatic plant, and better understand the effect humans have on their environment.
Students are able to go through the scientific process and test their hypothesis, create their own concentrations, and determine growth and toxicity rates of their plants.
Students are able to go through the scientific process and test their hypothesis, create their own concentrations, and determine growth and toxicity rates of their plants.
Context for Use
This lab has been used in a high school lab setting for biology, chemistry, and environmental science students. The lab set-up, data collection, and analysis takes approximately a week and a half. Students must learn how to count Duckweed fronds and not plants. This lab could easily be adapted to test for different variables such pH, lighting, fertilizer concentrations and nutrients, temperature, etc. Duckweed for this lab was purchased from a science company, but also could be collected in local outdoor aquatic environments.
Description and Teaching Materials
Materials are all listed in the lab procedure. This can be done in a lab or classroom environment as long as there is a source of light.
Students were told they would be doing a lab activity over the course of a week and a half. They started on Day 1 with a Pre-Test and then went through a powerpoint to learn about bioassays-what they are and how they are used, and then set up their lab experiment(50-60 min). On Day 3, students collect data by counting Duckweed fronds and we discuss observations and class averages(20-30 min). On Day 5 students again collect data by counting fronds,start creating their graph, and discuss class averages(20-30 min). On Day 8, we collect our final data, clean up lab materials, go over graph, and discuss analysis techniques. On Day 9 lab data sheets are collected, final observations are made, a class graph is shared and discussed, and a post test is given(30 min.)
Lab Procedure and Data Collection Sheet (Microsoft Word 57kB Aug2 09)
Pre/Post Test (Microsoft Word 24kB Aug2 09)
Duckweed Powerpoint (PowerPoint 902kB Aug2 09)
Duckweed Lab Wrap-Up (Microsoft Word 30kB Aug2 09)
Mathmatical Analysis (Microsoft Word 2007 (.docx) 14kB Aug2 09)
Students were told they would be doing a lab activity over the course of a week and a half. They started on Day 1 with a Pre-Test and then went through a powerpoint to learn about bioassays-what they are and how they are used, and then set up their lab experiment(50-60 min). On Day 3, students collect data by counting Duckweed fronds and we discuss observations and class averages(20-30 min). On Day 5 students again collect data by counting fronds,start creating their graph, and discuss class averages(20-30 min). On Day 8, we collect our final data, clean up lab materials, go over graph, and discuss analysis techniques. On Day 9 lab data sheets are collected, final observations are made, a class graph is shared and discussed, and a post test is given(30 min.)
Lab Procedure and Data Collection Sheet (Microsoft Word 57kB Aug2 09)
Pre/Post Test (Microsoft Word 24kB Aug2 09)
Duckweed Powerpoint (PowerPoint 902kB Aug2 09)
Duckweed Lab Wrap-Up (Microsoft Word 30kB Aug2 09)
Mathmatical Analysis (Microsoft Word 2007 (.docx) 14kB Aug2 09)
Teaching Notes and Tips
For this lab I made a stock 100% solution which was a mixture of 20% Miracle Grow Liquid Fertilizer and 80% water. Use more then 100 mL of solution in your sample cups if you wish to do this lab for longer then a week-we did run in to a couple samples evaporating.
Assessment
I gave the students both a pre and post test to determine gains in knowledge. I also graded their lab reports which they handed in with their data, analysis, and conclusion.
Standards
B. Scientific Inquiry
1.The student will design and complete a scientific experiment using scientific methods by determining a testable question, making a hypothesis,designing a scientific investigation with appropriate controls, analyzing data, making conclusions based on evidence and comparing conclusions to the original hypothesis and prior knowledge.
3. The student will apply mathematics and models to analyze data and support conclusions.
4. The student will identify possible sources of error and their effects on results.
1.The student will design and complete a scientific experiment using scientific methods by determining a testable question, making a hypothesis,designing a scientific investigation with appropriate controls, analyzing data, making conclusions based on evidence and comparing conclusions to the original hypothesis and prior knowledge.
3. The student will apply mathematics and models to analyze data and support conclusions.
4. The student will identify possible sources of error and their effects on results.