Week 8 Lab 9 Photosynthesis

Note: All your answers to questions must be in Red or other color (not including blue) for easier grading. Points will be deducted if you do not distinguish your answers. Lab 9. Photosynthesis Objectives:  Visualize and describe the separation of spinach pigments by paper chromatography  Describe the role of carbon dioxide in photosynthesis  Use a CO 2 Gas Sensor to measure the amount of carbon dioxide consumed or produced by a plant during respiration and photosynthesis.  Determine the rate of photosynthesis of a plant. Vocabulary:  Photosynthesis  Cellular Respiration  Chromatography Introduction: Before beginning this exercise, it is necessary to understand that photosynthesis uses light energy to synthesize carbohydrate from carbon dioxide. The equation is below. 6CO 2 +6H 2 O+Energy→C 6 H 12 O 6 +6O 2 This process requires light for some of the reactions. It is also necessary to understand that the plant is constantly undergoing cellular respiration according to the equation below. C 6 H 12 O 6 +6O 2 →6CO 2 +6H 2 O+Energy Notice that these two equations appear to be opposites. When plants are exposed to light, photosynthesis and cellular respiration both occur. In the dark, only cellular respiration occurs. We will study photosynthesis in an aquatic plant ( Elodea ) We can measure the rate of photosynthesis and cellular respiration by measuring the amount of CO 2 produced or consumed by the plant. Carbon dioxide combines with water to form carbonic acid (H 2 CO 3 ) which dissociates into hydrogen ions (H + ) and bicarbonate ions (HCO 3 - ). The pH drops due to the presence of hydrogen ions. CO 2 +H 2 O↔H 2 CO 3 ↔H + +HCO 3 - Respiring plants release CO 2 into the water, causing the pH to decline. During photosynthesis, plants take up CO 2 and the pH increases.

paper should be able to reach to within 1 cm of the bottom of the tube but not touch the bottom.  When the apparatus is adjusted properly, remove the paper so that you can add pigment extract.  Roll a coin on top of the leaves above where you placed the dot. At the end you should have a dark green line right on top of where you placed your dot. See figure above.  Using your disposable pipet transfer about 1 mL of chromatography solution. Caution! This step should be done under the fume hood.  Place your chromatography paper back on the hook and place it in the tube. The chromatography solution just barely touches the bottom of the chromatography paper. It should not pass beyond the point where you drew your dot. If the chromatography paper is not touching the solution, add more solution until it does.  Leave the assembled chromatography apparatus in the test tube rack. Leave it for about 10 min. However, you want to make sure you check it frequently, so the solution doesn’t reach the top of the paper.  When the solvent is about 1 cm from the top edge of the paper, remove the paper. With your pencil mark where the solvent has stopped.  Leave the paper to dry under the fume hood. Dispose of the chromatography solution according to your instructors' instructions.  After your chromatography paper has dried, bring it to your table and observe the different pigments separated on the paper.  Measure the distance in millimeters (mm) from the original dot to the top of the each of the pigments and solvent. Record your results on Table 1.  Calculate the R f (ratio-factor) values for each pigment and record your results on Table 1. The formula to calculate the R f is: R f = (distance moved by the pigment)/ (distance moved by the solvent). Figure 1: Chromatography apparatus assembly.

Results: (Watch the Lab 9. Photosynthesis video) Draw or insert picture of your Chromatography Paper. Table 1. R f Values for Each Pigment Pigments Distance moved (mm) R f Values Caratones 103 mm 0.936 Xanthophylls 58 mm 0.527 Chlorophyll a 38 mm 0.345 Chlorophyll b 19 mm 0.172 Solvent 110 mm 1 Conclusion: 1. Which pigment traveled the greatest distance and how does that correlated with the R f value you obtained? A pigment that is most soluble will travel the greatest distance thus in this experiment, caratones is capable of dissolving in the solvent. It is the most nonpolar of the pigments and it is captivated by the acetone mixture than to the paper. It has 103 mm in distanced moved, and in Rf Value, 0.936. 2. Would you ever get a R f value greater than 1? No. An Rf value can never be greater than 1 because the solvent is faster than the pigments . If the Rf value is greater than 1 then that would imply that

Part 2. Measuring the Rate of Photosynthesis using CO 2 Background Information: Plants make sugar, storing the energy of the sun into chemical energy, by the process of photosynthesis. When they require energy, they can tap the stored energy in sugar by a process called cellular respiration. The process of photosynthesis involves the use of light energy to convert carbon dioxide and water into sugar, oxygen, and other organic compounds. Cellular respiration refers to the process of converting the chemical energy of organic molecules into a form immediately usable by organisms. All organisms, including plants and animals, oxidize glucose for energy. Often, this energy is used to convert ADP and phosphate into ATP. Using the CO2 Gas Sensor, you will attempt to monitor the carbon dioxide consumed or produced by plants. Question: How do plants exposed to the light or dark affect their rate of photosynthesis when measuring CO 2 ? Hypothesis: If the concentration of carbon dioxide was increased, then the rate at which photosynthesis occurs will also increase. Materials:  Aquatic plant ( Elodea )  (1) Lamp with a halogen light bulb  Aluminum foil paper  (1) Vernier CO 2 sensor  (1) 250 mL Nalgene Bottle  Timer  Forceps  Beaker with 900 mL of water  Smartphone with application Vernier Graphical Analysis. Procedure: 1. Obtain a small amount of Elodea and place it into the Nalgene bottle. 2. Make sure you use your forceps to push down the plant so when the CO 2 sensor is inserted, it’s not being touched. 3. Using the Vernier Graphical Analysis application, ensure that your CO 2 sensor is connected. 4. Set it up to record for 300 seconds every 30 seconds. The application will record your data. Change units to (ppt) for CO 2 . 5. Place the CO 2 sensor into the Nalgene bottle and let it equilibrate for 5 minutes. 6. After 5 minutes, place the beaker with water in front of the lamp, this will be absorbing the heat from the lamp. Turn on your lamp.

7. Start collecting your data. Record your results on Table 2. 8. Remove the CO2 sensor from the bottle, turn off your lamp, allow CO2 to re-enter the bottle for 3 minutes. Make sure the CO2 sensor is kept upright! 9. After the 3 minutes, reinsert the CO2 sensor into the Nalgene bottle, start a timer for 5 minutes to let the sensor to equilibrate. 10. After 5 minutes, start collecting your data again, remember to turn on the lamp. 11. Repeat steps 8 – 10 for your third trial. Remember to turn off your lamp after the third trial. 12. After you finish collecting your data for your third trial, remove the CO2 sensor. 13. Start a timer for 5 minutes to allow CO2 to re-enter the bottle. You can blow some CO2 into the bottle. In the meantime, wrap the bottle in aluminum foil. 14. After 5 minutes, re-insert the CO2 sensor into the Nalgene bottle. Start a timer for minutes to let the sensor to equilibrate. 15. After 5 minutes, start collecting your data and recording your results on Table 3. 16. After you finish collecting your first trial, remove the CO2 sensor from the bottle, and start a timer for 3 minutes. 17. After the 3 minutes, re-insert the CO2 sensor into the Nalgene bottle, start a timer for 5 minutes to let the sensor to equilibrate. 18. After 5 minutes, start collecting your data again, record your results in Table 3. 19. Repeat steps 16 – 18 for your third trial. 20. Clean up according to your instructor’s instructions. Results: (Watch the Lab 9. Photosynthesis video) Table 2: Rate of Photosynthesis in the Light Time (s) Trial 1 Trial 2 Trial 3 Average 0 0.435 0.293 0.255 0.32767 30 0.427 0.284 0.246 0.319 60 0.417 0.267 0.239 0.30767 90 0.401 0.258 0.229 0.296 120 0.391 0.250 0.223 0.288 150 0.382 0.242 0.214 0.27933 180 0.375 0.233 0.207 0.27167 210 0.368 0.226 0.197 0.26367 240 0.359 0.218 0.191 0.256 270 0.347 0.210 0.183 0.2467 300 0.338 0.202 0.177 0.239

Table 3: Rate of Photosynthesis in the Dark Time (s) Trial 1 Trial 2 Trial 3 Average 0 26.810 19.362 13.028 19.7333 30 26.812 19.377 13.048 19.7457 60 26.862 19.400 13.048 19.77 90 26.870 19.405 13.053 19.776 120 26.845 19.393 13.066 19.768 150 26.901 19.410 13.074 19.795 180 26.904 19.390 13.083 19.7923 210 26.900 19.367 13.082 19.783 240 26.928 19.390 13.061 19.793 270 26.896 19.389 13.071 19.7853 300 26.865 19.391 13.056 19.7707 Graph: Graph your data below. There will be 2 separate graphs. Draw a line of best fit for each data set.

Photosynthesis Rate: The slope of your lines will represent the rate of each of your samples: Rate of Photosynthesis in the Light: y = -0.0003x + 0.3254 Rate of Photosynthesis in the Dark: y = 0.0001x + 19.753 Conclusion: 1. Were either of the rate values a positive number? If so, what is the biological significance of this? Yes. The biological significance of this is that carbon dioxide is produced during respiration. This causes the concentration of CO2 to increase, as sugar is oxidized and broken into CO2, water, and energy. 2. Were either of the rate values a negative number? If so, what is the biological significance of this? Yes. The biological significance of this is that oxygen is consumed during cellular respiration. This cause the concentration of oxygen to decrease as glucose is oxidized for energy. 3. Do you have evidence that photosynthesis occurred in leaves? Explain your answer. Yes, the rates of CO2 were lower when the flashlight was shown since the plant used the light but also from the air it took the carbon dioxide so it could go through photosynthesis. 4. List five factors that might influence the rate of carbon dioxide production or consumption in leaves. Explain how you think each will affect the rate? Influential factors are as follows. Oxygen/Temperature, during hot weather the limiting factor of high levels of oxygen in leaf cells reduce the amount of CO2 to convert in photosynthesis; and during cold weather the colder it is the slower the rate is. Carbon dioxide, the more CO2 concentration there is, the faster the rate is. Water supply, the less water available, the probable the plant will wilt and not absorb sunlight. Light intensity, the more there is the faster the rate is or increases. Chlorophyll, is a vital role because it converts light energy into chemical energy; therefore, a plant deficient in chlorophyll will absorb less light, which will lower the rate of photosynthesis. 5. Was your null hypothesis accepted or rejected? Why? The hypothesis was supported. When plants are exposed to light,