This is a lab report I created in my Biology lab class at the University of Idaho. This piece of work shows that I am capable of conducting a scientific experiment and writing scientific lab reports.

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Samantha Rae
Bio 114 Lab-05
02/14/2018
Duckweed Lab Report
Introduction: Population ecology studies the abiotic and biotic factors that influence the growth
rates of populations. It is important to understand how organisms are influenced by the abiotic
factors because some species are invasive and can harm the other species living in the same
ecosystem. A large population of Lemnoideae can cover the surface of a lake and decrease the
amount of oxygen other organisms need to survive. Research indicates that the ability of
duckweed to float on water and have their major surface exposed continuously to sunlight makes
them one of the fastest growing plant species on earth (Wang and Messing 2011).
This experiment investigates the growth of duckweed in response to sunlight exposure.
This organism was used because it can reproduce asexually and rapidly. The hypothesis that was
tested was that sunlight is a limiting factor for duckweed growth. It was predicted that the
duckweed exposed to more sunlight will have a higher population.
Methods: Four separate cups, each containing 100ml of water were created. 10 duckweed
individuals were placed in each cup as the starting sample size of each population. Cup A was
the control cup and was placed under the grow lamp to receive the same amount of sunlight each
day. Cup B was placed in the window sill to receive natural sunlight. Cup C had a black paper
cover over the top to replicate darkness and was placed on top of the fridge in the room. Cup D
was placed on top of the fridge as well with no cover to receive artificial light. The dependent
variable was the population growth in each cup. The independent variable was the amount of
sunlight each cup received. To control for other variables such as temperature and nutrients, each
cup was filled with tap water with no nutrients and placed into the same room which had the

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same temperature. The population of each cup was counted and recorded every Monday,
Wednesday, and Friday and the water was refilled so it was always at 100ml.
Results: Figure 1 shows the duckweed populations in each cup after twenty-one days. The
duckweed exposed to the most sunlight in cup A had the highest population. The duckweed
exposed to natural sunlight in cup B had the second highest population. The duckweed with the
black cover in cup C had the third highest population. The duckweed exposed to the artificial
sunlight in cup D had the lowest population.
Discussion: The above data reflects the prediction that the duckweed exposed to more sunlight
will have a higher population because cup A which was exposed to the most sunlight out of the
four cups had the highest population of duckweed. The hypothesis that sunlight is a limiting
Figure 1. illustrates the duckweed population in each cup over twenty-one days. Cup A, in
yellow, which was exposed to the most amount of sunlight had the highest duckweed
population. Cup B, in green, was exposed to natural sunlight and had the second highest
duckweed population. Cup C, in black, had a black cover over the top and had the third
highest duckweed population. Cup D, in red, was exposed to artificial sunlight and had the
lowest duckweed population. This line graph shows that the cups exposed to a greater
amount of sunlight had a higher population of duckweed.

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factor for duckweed growth was supported by the data because the cups exposed to the least
amount of sunlight had the lowest populations of duckweed. According to William Hillman
(1961) Lemnaceae can be found at all light intensities from full sunlight to dense shade. In this
experiment the duckweed survived better in full sunlight compared to artificial lighting, which
could be due to different species of duckweed preferring different amounts of light.
One problem in this experiment was the death of many of the duckweed fronds despite
having water and sunlight. David Kuhn (1969) states that a good light source and nutrient
solution is necessary for the maintenance of duckweed cultures. Nutrient availability could have
been a reason why the duckweed in this experiment did not reproduce as rapidly as expected and
why some of the fronds died. Another issue was in the recording of the data. The number of
duckweed individuals was counted differently between each observer which led to some
misleading data points. If this experiment was conducted again the duckweed in each cup would
be provided with the same amount of nutrients in the water and the observers would count the
duckweed individuals in the same way. Despite these problems this experiment supported the
hypothesis that sunlight is a limiting factor for duckweed growth.
Literature Cited:
Hillman W. 1961. The Lemnaceae, or Duckweeds: A Review of the Descriptive and
Experimental Literature. Botanical Review. 27(2):221-287.
Kuhn D. 1969. The Duckweed. The American Biology Teacher. 31(5):328-329.
Wang W and Messing J. 2011. High-Throughput Sequencing of Three Lemnoideae (Duckweeds)
Chloroplast Genomes from Total DNA. PLoS ONE. 6(9):1-10.