A few weeks ago, a mid-twenties entrepreneur conducted an experiment with duckweed. His results showed a clear pattern dealing with the population growth and carrying capacity of the area. Chase Hill, now the current Chief Marketing Officer at the Utah Carpet Cleaners, wrote up the report and is as follows:
Question: How does the level of salinity affect the growth of duckweed?
Hypothesis: The lower the salinity, the better the duckweed will grow.
Materials: Petri dish, 4 pipettes, spatula, 9 labeled test tubes, test tube rack, graduated cylinder, spring water, lemna minor fronds
1) Label the 9 test tubes: 3 of “low” salinity, 3 of “medium” salinity, 3 of “high” salinity.
2) Fill each of the tubes with 50 mL of spring water.
3) For the “low” salinity tubes, place 3 drops of salinity solution in each tube. For the “medium” place 6 drops, and for the “high” place 9 drops of the solution in the correct labeled test tubes.
4) Place three lemna minor fronds in each of the 9 test tubes.
5) Observe the test tubes 7 times over the course of a few weeks. Record the data in data sheets.
Control: Test tube with spring water and 3 fronds, no saline solution added
Independent Variable: Level of salinity in each of the test tubes
Results: Over the course of a few weeks, all of the tubes containing fronds, regardless of the salinity, generally grew at the same rate. All of the tubes showed signs of growth. We determined that in these particular circumstances, the carrying capacity was 5 or 6 fronds. Below, are graphs illustrating the data we collected.
Analysis: Our results did not fully support our hypothesis. We thought that the fronds would have a higher growth rate with a lower salinity level. But, as we found out, the duckweed grew at the same rate throughout all the test ranging from “low” levels of salinity, to “high”.
Our results weren’t too far off from our hypothesis because we knew that as duckweed is a freshwater plant, it would struggle to survive in salty water. Our results were very similar to what we anticipated, as we observed very little growth from the medium and high saline tests. What we found out that differed from our hypothesis, was that even the “low” saline tests showed a low growth rate as well.
One uncertainty we had when observing each day, was that we weren’t always able to tell if the fronds had actually germinated new growth.
If we were to do this lab again with changes to further our findings, we would start with a lower saline level for our “low” labeled tests. Since the carrying capacity was the same for the “low” saline tests as the “high”, we would want to lower the “low” saline levels to see if we could increase the growth rate and carrying capacity.
This would help improve our data and better answer our experiment question. Overall, we conducted our experiment the way we designed it to be, and although our results differed from our hypothesis, they answered our question.
Overall, the experiment made it clear that populations and carrying capacities can be affected by so many external variables.