Environmental Science Lab Report

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Estimation of Duckweed Geometric Population Density
Phosphate Depletion
By Ana Rosina Alarcon
University of Texas at El Paso
Department of Environmental Science
Instructor: Gebregiorgis Alay G.

Duckweed is a small aquatic plant that is able to grow rapidly, making it the ideal specimen for our experiment. It is hypothesized that altering the amount of light received by duckweed will alter its photosynthetic rate. It is predicted that a lower light intensity will lower the rate of growth in duckweed. Also is an important high-protein food source for waterfowl and also is eaten by humans in some parts of the world. As it contains more protein than soybeans, it is sometimes cited as a significant potential food source. The tiny plants provide cover for fry of many aquatic species. The plants are used as shelter by pond water species such as bullfrogs and bluegills. They also provide shade and, although frequently confused with them, can reduce certain light-generated growths of photoautotrophic algae. The plants can provide nitrate removal, if cropped, and the duckweeds are important in the process of bioremediation because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen and phosphates. For these reasons they are touted as water purifiers of untapped value. For Lab 7, the duckweed lab, the purpose is to test what factors might affect the growth of duckweed. In this case phosphate was taken away from the nourishment given to the plant; this was to see how it might affect the plants growth rate after a few weeks. As the weeks went by a significant difference between the duckweed samples without phosphate and the samples with phosphate was noticeable, the duckweed without phosphate had a lower growth rate. This goes to show that in a case where growth rate of plants is important phosphate must be present to raise the growth rate significantly for the first few weeks.             This is important in a case where duckweed might be being used as a nutrition source of a certain organism, knowing that phosphate is crucial for healthy duckweed growth comes in handy to be able to have the maximum growth rate available and have the duckweed be a reliable nutrition source for the specific organism being fed the duckweed. Since this plant is high in protein it is a good nutrition source, so it is a good idea to grow a supply of the plant at home in case of a drastic emergency, were the only sources of protein have become scarce and perhaps being able to grow this plant rapidly help a person get the source of protein they need to survive and live a healthy life. Or in other cases where duckweed is used as a novel feedstock for bioethanol production by Saccharomyces cerevisiae (energies), whatever the use is for, there is high interest on what conditions the plant grows the best in, and in this experiment the point is to find out how phosphate will affect the plant. METHOD:

            To begin this experiment three plastic cups are needed. These cups will be the place where the duckweed will be grown for a period of three weeks. Fill three cups with 200ml of MLB water which will be the control groups for the experiment; these cups will start off with 15 plants each. Then repeat the process for the other three cups but fill them with 200ml of phosphate lacking water as the experiment group. Count the number of thalli (leaves) in each cup and record that number (this will be used to determine the growth rate later in the experiment). Record all the information of the number of thalli in a graph labeled control and phosphate groups to keep track of which is which and to be able to determine growth rates; start off with day zero and initial number of thalli, followed by day 7th, 14th, and 21st.             After gathering all the information about the growth of the number of thalli as the weeks go by, estimate the average growth rate of the control group and the...
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