Duckweed Bioassay Lab

Figure 6.

Method

Using the method below, you will determine duckweed sensitivity to various concentrations of a single fertilizer compound.

Materials

 Fluorescent of plant grow lights

 Duckweed plants-10 per sample cup

 Clear plastic cups (3 cups per concentration being tested, plus 3 cups for the control)

 Miracle-Gro Liquid Houseplant Food Drops (N:P:K = 8:7:6)

 Tweezers or paper clips (for handling Duckweed)

 Graduated cylinder-100 mL

 100 mL each of the chemical solutions to be tested

 Water for rinsing

 Permanent marker for labeling sample cups

Procedure

1. Determine which concentrations you will be using in the duckweed bioassay (100%, 10%, 1%, 0.1%, and 0.01%).

2. Label cups with your name and compound concentration. Each concentration should have 3 cups labeled with a,b,c (Ex. 10%a, 10%b, 10%c). Label 3 additional cups “control” a, b, and c.

3. Fill each sample cup with 100mL of specified compound concentration. Be sure to rinse the graduated cylinder with water when switching to a different concentration.

4. Using tweezers or an unfolded paper clip, gently transfer 10 duckweed plants into each cup. (Avoid using your fingers to reduce introduction of additional chemicals into culture.) Choose only green, healthy-looking plants that have two fronds apiece and are approximately the same size. 5. Carefully place sample cups under 24 hour fluorescent or plant grow lights.

6. Let the samples sit undisturbed until counting days-every two day. Do not add water.

7. Every two day growth period, count the number of fronds in each sample. Be consistent when counting so results will be comparable across treatments.

8. Record your data on the table, and make notes about any plants that are yellow, rootless, sinking, or otherwise appear unhealthy.

9. Graph the mean (average) number of fronds for each treatment as well as the control. Then analyze your data.

Name: ______Date ______

Chemical Tested ______Length of experiment ______days

Constants______

Variable to be tested: ______

My Hypothesis:

______

A Duckweed plant with 2 fronds looks like this:

A Duckweed plant with 3 fronds looks like this: Data Collection

Number of Duckweed plants with two fronds in each cup =______

Duckweed Bioassay Data

Solution # Duckweed Avg. # Comments about Plant Health Concentration Fronds/Cup Fronds a b c Control

Fertilizer Concentration ( %)

Fertilizer Concentration ( %) Fertilizer Concentration ( %)

Duckweed Bioassay Data Solution # Duckweed Avg. # Comments about Plant Health Concentration Fronds/Cup Fronds a b c Control

Fertilizer Concentration ( %)

Fertilizer Concentration ( %) Fertilizer Concentration ( %)

Duckweed Bioassay Data

Solution # Avg. # Comments about Plant Health Concentration Duckweed Fronds Fronds/Cup a b c Control

Fertilizer Concentration ( %) Fertilizer Concentration ( %) Fertilizer Concentration ( %)

Duckweed Bioassay Results

Lab Analysis

1. Did the duckweed colonies grow well in the control cups? Do your control plants appear healthy? If not, what would you recommend trying differently for the next round of experiments?

2. Did duckweed growth respond in a predictable way to concentrations? Describe any trends you observed. 3. Does any of your data not fit the trends you observed? If so, can you think of any reasons why this data might be outside the range you would expect?

4. What TC50 would you estimate based on your duckweed data?

TC50 =

If it is impossible to estimate the TC50 from your data, please explain why.

5. At which concentration did Duckweed show the most growth with?

6. What was the average growth rate for each of your 3 samples?