Victor MartinTuesday, October 7, 2014 AP Biology Third Block Primary Productivity Lab Report Only three percent of Earth is covered with freshwater ecosystems, and finding oxygen in these places is pretty deficient. Aquatic plants and photosynthetic protists depend on dissolved oxygen to assimilate carbon through photosynthesis. The amount of dissolved gases there are in aquatic ecosystems is dependent on many physical factors such as salinity, altitude, or even water temperature, but one of the main factors that come especially from organisms is respiration. Respiration requires oxygen and will usually decrease dissolved oxygen. However, photosynthesis of plants will increase dissolved oxygen. With this in mind, the measurement of dissolved oxygen concentration in a body of water is often used to determine whether the biological activities requiring oxygen are occurring, which can indicate pollution. In order to find this out, one can use the primary productivity, which is the rate at which carbon compounds or organic materials are stored. Plants and protists that possess photosynthetic pigments usually need sunlight to create newer organic compounds from simple inorganic matter. These organisms must acquire carbon from carbon dioxide in the water or air by following this equation: 6 H2O + 6 CO2 (g) + energy → C6H12O6 + 6 O2 (g) In order to measure primary productivity, one must determine the rate of oxygen production. This is done by calculating the amount of carbon that has been found in aquatic organisms for periods of time. Some other ways are finding the rate of carbon dioxide exploitation or even the rate of the formation of organic compounds. Another favorable way of measuring the production of oxygen is the light and dark bottle method. The dissolved oxygen concentrations of the body of water you will use can be measured and compared before and after incubation in light and darkness. The difference between the measurements of dissolved oxygen in the initial and dark bottles shows an indication of the amount of oxygen that has been consumed by respiration. The bottle that has the most darkness will show the most respiration, because of a dramatic decrease in dissolved oxygen. The other bottles exposed to light will have photosynthesis and respiration occurring all at once. Therefore, the change over time in dissolved oxygen concentration from the initial concentration is the measure of net productivity. The dissolved oxygen difference over time between the light bottle and the dark bottle is the total oxygen production and calculates the gross productivity. My hypothesis for this lab is that the if the organisms and plants found in each of the pond water have been exposed to darkness for many periods of time, the population of the organisms especially the protists and plants, would start to decline due to a lack of light. Because of this the test tubes that show approximately 100% to 65% of light, which includes test tubes 2 and 3, will show slightly a bit more respiration than the amounts of photosynthetic activity. The test tubes that show less than 50% of light, which includes test tubes 4 to 7, will show a much larger decrease in photosynthetic activity and more in respiration. The dark test tubes will definitely show significant loss in plant growth, and the organisms will be using more dissolved oxygen than before. This will increase the aerobic respiration for them. The purpose of this lab is to explain to others about using primary production, net production, and gross production to calculate respiration and other influences on the effects of light intensities in the dissolved oxygen quantities of aquatic ecosystems. When there is a noticeable change in the environment, other species will perform differently from others. One good example of this is when some type of agricultural fertilization has been leaking into a pond, many plant species, such as algae, will start to thrive, covering the entire pond. When this happens, the plants that flourish at the bottom of the pond will not get any sunlight, causing them to die. This effect will have the algae and decomposers to use up even more dissolve oxygen, causing an environment with a high biological demand. This problem is called eutrophication; this lab is based on these types of events. Using the different types of light exposure and darkness can help inform students how the dissolved oxygen will decrease each day of the experiment. Materials In this lab, you will need you will need a Lab Quest, along with a Lab Quest app installed, and a vernier dissolved oxygen probe.. You will also need seven test tubes, with 25 by 150 millimeter screw tops. Materials for the test tubes include aluminum foil, rubber bands, and 17 pieces of plastic window screen, with length and width measurements of 12 centimeters. You will also need a 250 milliliter beaker, distilled water, and 500 milliliters of pond, lake, or algal water. Pre-Lab Procedures Before each use, the Dissolved Oxygen Probe must be heated for ten minutes. To do this, you must remove the protective cap and unscrew the membrane cap, as shown in Figure 1. The membrane cap is located at tip of the probe. After that, you must use a pipet to fill the membrane cup with exactly 1 milliliter of the Dissolved Oxygen Filling Solution. Once you have finished, put the membrane cap back onto the electrode and put the probe into the 250 milliliter beaker filled with distilled water. After this, you then connect the probe with the Lab Quest and select New from the File menu. Then you wait for ten minutes until the probe warms up. After that, you can now calibrate the Dissolved Oxygen Probe. Remove membrane cap Add electrode filling solution Replace membrane cap Figure 1 shows the basic concept on how to warm up the Dissolved Oxygen Probe Day One Procedures After finishing up with the Pre-Lab, you must get the seven test tubes and fill them each with the pond water samples. There should not be any air bubbles in each of test tubes. You then use masking tape on the cap of each test tube and label them as dark, initial, 2%, 10%, 25%, 65%, and 100%. Now you wrap the seventh test tube with aluminum foil so it will remain in the dark. You must use the screen layers to wrap around the test tubes. Test tube 3 will have 1 layer. Test tube 4 will have 3 layers. Test tube 5 will have 5 layers. Lastly, test tube 6 will have 8 layers. These will represent the percentages you have written for each of them. Then you place the dissolved oxygen probe in the initial tube, where it should be submerged at approximately half the depth of the water. You will also need to move the probe up, so that the water will move past the tip of the probe. Once the dissolved oxygen reading has been sustained, you then record and place the probe back into the beaker. Then you place test tubes 2 to 7 near a light source. Day Two Procedures On Day 2, you must repeat the pre-lab procedure to polarize the probe and then place the probe into the test tube with 100% light, or just test tube 2. You then move the probe up and down again for 1 centimeter and wait for 60 seconds, or when it stabilizes. Then you do this for all the other test tubes. After this, you start cleaning the test tubes and rinse the probe with distilled water and put it back into the beaker. Results Table 1 Test tube Number of Screens % Light 1 2 3 4 5 6 7 0 0 1 3 5 8 Aluminum Foil Initial 100% 65% 25% 10% 2% Dark Table 1 lists the amount of coverage from the window screens you need to put on the test tubes. It also lists the seven test tubes you will use, along with how much light is exposed for each of them. Table 2 Test tube % Light DO (mg/L) 1 Initial 22.1 mg/L 2 100% 2.5 mg/L 3 65% 3.7 mg/L 4 25% 2.9 mg/L 5 10% 3.0 mg/L 6 2% 2.1 mg/L 7 Dark 1.9 mg/L Table 2 shows the results I got by pitting the probe in the water. Discussion Based on the data I have collected, the test tube with the highest amount of dissolved oxygen was test tube 3, with 3.7 milligrams per liter. Test tube 3 had 65% of light, including one screen layer. However, the initial test tube had 22.1 milligrams of dissolved oxygen per liter. The one with the lowest amount of dissolved oxygen was the dark test tube, with 1.9 milligrams per liter. The results for the other test tubes varied, which made the whole experiment very inaccurate and confusing. One major source of error that was probably how the Lab Quest either too old to understand the results, or how me and my group did not follow the procedures correctly. Whenever we put the probe into one of the test tubes, many numbers were varying and we picked the number that we saw the most. I don't find this to be correct, because the lab procedures did not precisely explain how to find the number. Another source of error was the amount of time we had to do this assignment. The procedure informs me that this whole lab was two days, but you really can't see any major results within two days. We should at least get around a whole week or two to see change in the experiment and such, but if it was because of how organized this school year is going to be, then maybe at least one week should do it. I also think that dissolved oxygen does not take a short time to affect the microorganisms found in the test tubes. It would have been better if we examined or even observed the test tubes to see if there were more organisms after the first day or not. I do like this lab; because it helps others see how an ecosystem can be affected after dramatic changes in the environment. Checking the percentage of light for each of the test tubes was fine, but there should have been more durable layers of a different material to show changes. Instead of using plastic window screens, we could use cloth, or even polyester to show how much light can be exposed. Overall, this lab was a good first lab for me, but there could have been more accessories, creativity, and more ways of thinking more like a scientist, instead of reading several pages and find several puzzling results from the experiment. Conclusion In conclusion, calculating the primary production, net production, gross production, and respiration of an aquatic ecosystem can be different based on the amount of light change for that environment. The amount of light exposed to the plants and protists in the test tubes effects the amount of dissolved oxygen used, which can mean how much respiration was made from all of the microorganisms in the test tubes. My hypothesis was correct; the test tubes with light exposures over 50% had the most dissolved oxygen and had the least respiration being produced. These results conclude that the environments had a low biological oxygen demand, since there was plenty of dissolved oxygen. However, the test tubes with 25% of light exposure all the way to darkness received less dissolved oxygen. This means that the plants were not able to make photosynthesis and made the most respiration, and the microorganisms had a high biological oxygen demand. This explains that the environment is not really growing, or there isn't any production except for respiration. I found this lab to be very interesting, because it introduces how we are going to do labs and how one little change can bring a heavy impact to the environment. Though finding the results could be a little irritating, the basic knowledge and understanding primary production is the key to this lab. I really did not get the best results, but understanding how to get the rate of respiration or the gross productivity is something that I learned from this lab and has helped me think about ecology and ecosystems in a another direction. There were many ways of making this lab better, but for a fresh start on something, this lab was pretty essential to me and the ecology unit itself. References 1. Masterman, David. Advanced Biology with Vernier: Experiements for AP and College Biology. Beaverton, Or.: Vernier Software & Technology, 2010. Print. 2. "Dissolved Oxygen and Primary Productivity Lab - Savage Science." Dissolved Oxygen and Primary Productivity Lab - Savage Science. Parish Episcopal School, n.d. Web. 04 Oct. 2014. <https://sites.google.com/a/parishepiscopal.org/savage-science/home/ap-biology/ap-biologylabs/dissolved-oxygen-and-primary-productivity-lab>. 3. "Lab 12: Dissolved Oxygen and Aquatic Primary Productivity." Lab 12: Dissolved Oxygen and Aquatic Primary Productivity. DesLee26, 23 Apr. 2011. Web. 04 Oct. 2014. <http://www.freezingblue.com/iphone/flashcards/printPreview.cgi?cardsetID=81287>. 4. "SCOPE 13 - The Global Carbon Cycle, Chapter 10, Primary Production in Aquatic Environments." SCOPE 13 - The Global Carbon Cycle, Chapter 10, Primary Production in Aquatic Environments. N.p., n.d. Web. 03 Oct. 2014. <http://www.scopenvironment.org/downloadpubs/scope13/chapter10.html>.