HP 8 Week Duckweed Growth Lab Report
Over the past weeks, our class has been testing the effect of beginning population size on growth rate and carrying capacity. Pairs of groups had the same number of duckweed at the start, except for one, the group that started with 50 duckweed. The hypothesis for all of the groups is the higher the starting population of duckweed, the faster the population will reach carrying capacity. This hypothesis was proved, because the group with the highest starting population was the only group to reach carrying capacity at the end of the eight week test period. Due to the exponential nature of duckweed growth, it took longer for the populations with five duckweed at the start of the experiment to grow as much as the population that started with forty duckweed. There are some outliers in the groups, which can most likely be explained by human error, counting large amounts of small, similar looking objects. The end of the experiment supported the hypothesis and showed the growth rate of duckweed. Someone could use this data while trying to invent a new way to manage duckweed growth in a body of water, or for a research or science fair project
This experiment used fluorescent and incandescent lights, set up over a table to hold the duckweed plants. The duckweed beginning populations were put in a small plastic cup and left under constant light, except for when they were counted weekly. The independent variable is the population size in the cup. Water levels decreased because of photosynthesis, and were refilled often to keep a dependent variable. One variable that could not be controlled was the temperature of the room. There are optimal temperatures that the duckweed can grow best in, and the grow lights can only create a small amount of heat.
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The growth of duckweed is exponential, meaning when one plant grows from the mother plant, the new leaf begins growing another plant, and so on. This creates the fast growing nature of duckweed. The data collected over the eight weeks demonstrate this growth, and demonstrate one group reaching carrying capacity. The growth rate for the populations with lower starting numbers were less than the populations with larger beginning populations, which caused the group that started with 50 duckweed plants, group 11 to reach carrying capacity at week 4. A strange result that occurred with the group that started with 40 plants; Groups 9 and 10 reached carrying capacity at week 7, but their carrying capacity was different. This could be caused by more time for the plants die due to their lessened starting plant population, which means a growth rate that is less than group 10. These both are results that strongly support the prediction made at the beginning of the lab, that the starting population of the duckweed would affect the time it takes to reach carrying capacity in the cups that were used.