Katie Gordon
Title- An Investigation of Algae’s Response to Being Exposed to Varying Light Levels
Introduction-
Photosynthesis is the process of converting sunlight energy into usable chemical energy. Photosynthesis takes in the energy from the sun along with carbon dioxide and water, in order to produce both sugar and oxygen. The oxygen is produced as a byproduct of photosynthesis, but is crucial for life on earth. The light taken is absorbed by either chlorophyll or carotenoids (Graham 2009). These primary pigments absorb light at only certain wavelengths. Most plants appear green because neither green or yellow are absorbed effectively by the photosynthetic pigments.
Organisms are able to photosynthetically process light between 4000-700 nanometers. This range of light is referred to as photosynthetically active radiation, or PAR. PAR is able to measure how many photons of light are passing through a specific area per second. The more intense the lights at a given time, the higher the PAR value would be. The rate of photosynthesis is also dependent upon the intensity of the light. The greater the light intensity the increased rate of photosynthesis is being performed by the algae.
Methods-
For this experiment there were three replicates and one control. For the experiment the DO meter had to be calibrated. Instructions for this task were presented in lab. A small stir bar was placed in each of the BOD bottles. The BOD bottles were then filled with a Pseudokirchneriella subcapitata (algae) culture, that was from the stock culture. The tube was placed in the bottom of the bottle and the spigot was slowly turned to minimize any mixing. Mixing could result in excess oxygen entering the system. All of BOD bottles were full, so that there was no air trapped when the stopper was put on. Tape was used to label each of the different bottles depending on the light treatment they received. One at a time the bottles were placed on the stir plate, and an initial DO reading was taken for each bottle. The probes were rinsed with distilled water both before and after taking the readings to protect against contamination. The bottles were then placed at the light intensity or PAR of 25.8 µmol photon/m^2/sec, and they were left there for 90 minutes. To maximize the light exposure for each of the bottles were each placed in a direct path to the light. The bottles were removed after 90 minutes, and the final DO readings were taken for each of them individually.
Results-
The data collected from each lab group got combined, and placed on a single graph in order to show the different levels of dissolved oxygen at different light intensities. Each group measured their bottles at different light intensities, ours were measured at 25.8. The initial value for the control at a light intensity of 25.8 was 1.10 mg/L, and the final DO reading was 1.07 mg/L. FOr R1 the initial was 1.03 mg/L, and the final reading was 1.43 mg/L. The initial reading for R2 was 1.07 mg/L and the final reading was 1.30 mg/L. The initial reading for R3 was 1.09mg/L and the final reading was 1.27 mg/L. On the graph below the blue represents the initial DO reading taken before the bottles were placed in the light, and the orange bar represents the final DO reading recorded. No obvious trend is apparent across the levels of oxygen dissolved and the corresponding PAR values. An ANOVA test was also run in order to test if the differences between the means were statistically significant. The p value recorded for the data collected was 0.6287. Based on this value, the changes present among the data were deemed to be insignificant.
Figure 1: The range of the PAR levels compared to the amount of oxygen dissolved at both 0 minutes and 90 minutes.
Discussion-
This lab was based off of the response of algae to varying light levels. Originally we thought that when the algae was exposed to a greater light intensity, the level of dissolved oxygen would correspond directly. Essentially, as the PAR would increase the level of photosynthesis would increase as well. However, based on the data collected from the different trials of the experiment done by the class, this idea was proved inaccurate. The data we collected did not show a specific trend among the varying PAR levels. The rate of photosynthesis did not correspond directly with the PAR value.
The results we collected in this lab were important because they proved that there is either no direct relationship between the two, or there was some error along the way that configured our data in that way. Based on a study by Hazem M. Kalaji and Parvaiz Ahmad, PAR values can actually have limits. Values that are too high or low can serve as stress factors, and therefor disrupting the photosynthetic process.
Literature Cited-
Kalaji Hazem, Ahmad Parvaiz. 2014. Emerging Technologies and Management of Crop Stress Tolerance,Volume 2 [Internet]. Science Direct [cited 2018 Mar 28]. Available from https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/photosynthetically-active-radiation
Peers Graham, Truong Thuy, Ostendorf Elisabeth. 2009. An Ancient Light-Harvesting Protein is Critical for the Regulation of Algal Photosynthesis [Internet]. La Jolla (CA): Nature International Journal of Science [cited 2018 Mar 27]. Available from https://www.nature.com/articles/nature08587#abstract
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[1] This paper was written for my General Biology ii lab last semester. It is a very simple lab report talking specifically about the levels of photosynthesis and the results the algae were experiencing when exposed to different levels of light. [2] Specific strengths and weaknesses from this type of writing are different compared to the pieces that I composed throughout this English course. My strengths on this project revolved more around making the most clear and concise statements to make my findings as specific as possible. Weakness occurring in this piece I believe were from the introduction, where I could have elaborated more on specific aspects of background information in order to give the reader a greater level of understanding.
