Every Group Completes one lab write-up with the following sections: Title Effects of 85% light blocking filter on the Rate of Photosynthesis/Cellular Respiration Purpose: The purpose of the Photosynthesis/Cellular Respiration Lab is to determine whether photosynthesis or cellular respiration will become more dominant under an 85% light blocking filter. Hypotheses: 4 total. One for each cuvette. Use the Indicator Color guide and your knowledge of Cellular Respiration and Photosynthesis to predict the approximate color the CO2 indicator will turn. (Ex: More yellow or more purple). Light Control Hypothesis: If a cuvette with algae beads is placed under white light, then the pH won’t reach 6.9. The CO2 indicator will stay at the initial color of purple. Dark Control Hypothesis:If a cuvette with algae beads surrounded by foil is placed under white light, then the pH will reach 6.9 at a fast rate. The CO2 indicator will eventually turn yellow from purple. Light IV Hypothesis: If a 85% light filter is placed over the cuvette with algae beads under white light, then the pH will be decreasing towards 6.9 at a faster rate. The CO2 indicator will eventually turn yellow from purple. Dark IV Hypothesis: If a 85% light filter is placed over the cuvette with algae beads under white light but covered by foil, then the pH will be decreasing towards 6.8 at a much faster rate. The CO2 indicator will eventually turn yellow from purple. Data Table: Look at the CO2 Indicator Color Guide. Every 5 minutes for every tube you are recording the indicator color as well as the corresponding pH/A550 ● Type any observations in the box BELOW the data table during the data collection period that may be pertinent to your data analysis/conclusions later on. Time (min) Control Light Indicator Color/pH Control Dark Indicator Color/pH IV - 85% filter Light IV - 85% filter Dark 0 8.7 8.7 8.7 8.7 5 8.5 8.5 8.7 8.7 10 8.5 8.5 8.5 8.7 15 8.5 8.3 8.5 8.7 20 8.3 8.3 8.3 8.5 25 8.3 8.3 8.3 8.3 30 8.3 8.3 8.3 8.2 35 8.3 8.3 8.3 8.2 40 8.3 8.3 8.3 8.1 45 8.3 8.3 8.3 8.1 Observations (do not need to be in complete sentences) pH stayed capped at 8.3 whereas IV Dark went to 8.1 pH. This could be because it had the least amount of light possible therefore maximizing the amount of CO2 produced during cellular respiration and lowering the PH Graph: You will be putting 4 lines on one graph. Be sure to provide a legend. You will be graphing time on the X-Axis and pH/Absorbance on the Y-axis. Once you plot your data points, make a line of best fit for each cuvette. Use graph paper and a ruler. Insert a CLEAR image below. Calculations: For each cuvette, calculate the slope of the line. You can do this on paper by hand and insert a picture or show your work electronically. Be sure to use units! Analysis: complete the following table Control: Light Cuvette ● Control: Dark Cuvette I.V. 85% filter Light Cuvette I.V. 85% filter Dark Cuvette Rate? (Use correct units) -0.0089 pH/min -0.0089 pH/min -0.0089 pH/min -0.0133 pH/min Slope Positive or Negative? Negative Negative Negative Negative CO2 increased or decreased? Increased Increased Increased Increased PSN or CR dominant process? CR Dominant CR Dominant CR Dominant CR Dominant Conclusion: CER ○ Claim: State the effects your independent variable had on the rate of CO2 absorption in both the light and dark cuvettes compared to the control cuvettes. ○ Evidence: Use appropriate evidence from your data analysis table. ○ Reasoning: Scientific reasoning why you got the results you got. Claim: When placed under a 85% light blocking filter, the CO2 absorption was increased in the dark cuvette when compared to the control light and dark cuvette, and the CO2 absorption was unaffected in the light cuvette when compared to the control light and dark cuvette. Evidence: All of the 4 cuvettes, in both control and IV, all started at a pH of 8.7, throughout the 45 minutes of data collection, the control light cuvette decreased to a pH of 8.3, the control dark cuvette also decreased to a pH of 8.3, the 85% filter light cuvette decreased to a pH of 8.3 as well, and the 85% filter dark cuvette decrease to a pH of 8.1. The slope at which the pH changed, is negative for all 4 cuvettes, as they decreased. The slope is -0.0089 pH/min for the control light, control dark, and 85% filter light, and is -0.0137 pH/min for the 85% filter dark. Reasoning: The products of Photosynthesis are oxygen and glucose. The products of Cellular Respiration are water, ATP, and CO 2. In aquatic plants, such as the algae in this experiment, these two processes occur hand in hand, the CO2 from the water, and water itself is used for photosynthesis, which then provides the O2 and glucose to then be used in Cellular respiration, producing more CO2 and water, and the cycle continues. When there is a lack of light and photosynthesis cannot occur, cellular respiration is the dominant process and thus a net CO2 output is emitted. In our experiment the Control dark cuvette, and the 85% filter dark cuvette, both had a decrease in the pH, going from 8.7 to 8.3 and 8.7 to 8.1 respectively(3). This decrease in pH means that a net amount of CO2 was emitted from the algae beads and dissolved into the water, cellular respiration was the dominant process with a lack of light. When there is light present, photosynthesis generally tends to be the dominant process and thus there is no net output of CO2 from the plant, instead there is a net output of O2. However, in our experiment in both the control light and 85% filter light cuvettes, we saw a decrease in pH, with both(2) going from 8.7 to 8.3 pH, meaning a net production of CO2. (see error analysis(1)). Error analysis: (1) A possible explanation for why there was a production of CO 2 in the light cuvettes for both the control and 85% filter, is that light reaching the algae beads was not bright enough, and the compensation point for photosynthesis was not able to be reached. This can be due to a variety of factors. The bulb was not bright enough to provide the amount of lumens needed for the algae’s compensation point, the cuvette or solution inside could have refracted the light, potentially lowering the brightness of light reaching the algae bead, or a combination of the two. (2) There should also be a distinction between the rate of change in the Control and 85% filter light cuvettes. In our experiment, the slopes were both the same at -0.0083 pH/min. Since the filter blocks light, the slope for the 85% filter light cuvette would be expected to have a more negative slope. The reason that this is not the case could be due to again a variety of reasons. One could be that both cuvette’s were placed under different bulbs, that potentially have a different lumen output, and/or differences in algae beads in their rate of cellular respiration production. (3) This difference in the rate of cellular respiration of the algae beads themselves can also be attributed to the difference in slope between the control dark and 85% filter dark cuvettes, being -0.0083 and -0.0133 pH/min respectively. Since both are wrapped in foil, they should not be receiving light regardless of a filter lowering the brightness, and the change in slope is most likely due to the differences in the algae beads of each cuvette.
