Photosynthesis Lab Questions
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Pigment Lab-What is the formula for Rf value? Draw out an example of a chromatography paper result and explain.
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Divide the distance the pigment traveled by the distance the solvent traveled.
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Pigment Lab-What 2 properties determine how far a pigment will travel in paper chromatography? How would you determine each property if given the structure of a pigment?
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Polarity and Molecular Mass Molecular mass would be determined by adding up the molar masses of each atom in the structure. For Polarity, the functional groups determine the polarity. CH3 makes the molecule more non-polar, while OH or Carboxyl groups make it more polar.
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Pigment Lab-What are 2 similarities between gel electrophoresis and paper chromatography?
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Gel electrophoresis and paper chromatography both are used to separate molecules. In both, smaller molecules travel further.
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Pigment Lab-What are 2 differences between gel electrophoresis and paper chromatography?
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Chromatography uses paper and a solvent, while electrophoresis uses a gel and electricity. In chromatography, molecules move due to their solubility in the solvent and capillary action. In electrophoresis, molecules move because they are attracted to the charge of one of the electrodes.
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Pigment Lab-If water were used instead of acetone and petroleum ether, would the results for the chromatography experiment be the same? Explain.
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Water is polar, while the petroleum ether and acetone mixture is non-polar. Thus, the more polar substances would have traveled further and the more non substances would have traveled less far.
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DPIP Lab-If you get a large transmittance for the trial of the cuvette kept in the dark, what might be an explanation?
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Perhaps the cuvette was not put into the foil wrapping fast enough after checking data, or maybe the foil wrapping was too loose or had a hole in it.
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DPIP Lab-If you get a large change in transmittance for the trial of the cuvette with boiled chloroplasts, what might be an explanation?
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Perhaps the chloroplasts were not boiled thoroughly enough or the non-boiled chloroplasts were put in by mistake instead of the boiled chloroplasts.
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DPIP Lab-If only green light were used in the experiment, instead of white light, how would you expect the results to be?
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Green light wavelengths are not used for photosynthesis. There would be no reaction.
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DPIP Lab-Does DPIP reduced or oxidized? What does this mean? What molecule plays this role in the light reaction?
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DPIP gains electrons, thus it was reduced. This replaces NADP in the light reaction since DPIP has a higher affinity for electrons than does NADP.
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DPIP Lab-If you do not see a reaction in the positive control, what might explain this?
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Perhaps chloroplasts were not added, or perhaps the cuvette was kept in the dark, or perhaps the chloroplasts had been somehow destroyed and the enzymes denatured (heat, acid, etc)
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DPIP Lab-If you test putting the chloroplasts in the fridge, vs at room temperature vs at warm temperature (80 F or 27 C), show what the resulting graph would likely look like.
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The graph for cold temperature should go up (as long as the light is on in the fridge) but more slowly than room temp. The warm one should go up more quickly.
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DPIP Lab-If we were to run the lab for an hour, rather than 15 minutes, draw what the positive control like would look like. Explain why it would look this way.
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The line would go up as you saw it do in the lab, but then level off. Eventually all of the DPIP would be reduced and the color could no longer change. Photosynthesis would still be occurring though.
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DPIP Lab-Why did we have to use a chloroplast solution rather than a real plant for this lab?
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There is no way to add DPIP to a plant
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DPIP Lab-Name another independent variable, not tested in this lab, that would be interesting to test. Explain how you could test that in a controlled way.
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Answers will vary
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Pigment Lab-Let's say you have a mixture containing Pigment A that has a molecular mass of 40g/mole Pigment B that has a molecular mass of 99 g/moles Pigment C that has a molecular mass of 97 moles g/mole. Pigment A has many OH groups, as does Pigment B, but pigment C has mostly methyl groups and no OH or carboxyl groups. The solvent being used is water. Draw a chromatography strip showing how far each would go.
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The strip should show that pigment A went the furthest, while pigment B went the next furthest and pigment C when the least far. The molar mass of B and C is very close, but the fact that C is more non-polar and the solvent is polar would make B go further than C.
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DPIP Lab-What effect would adding more DPIP to each experimental tube have on the experimental results shown in the graphs below? Sketch your answer and explain.
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The solution would be darker, so the curve would be shifted down. Also, there would be more DPIP, so it would likely take longer for it all to be reduced. Thus it would level off sooner.
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DPIP Lab-What is the best explanation for the results seen in the graph below if the student thought they were setting up the positive control. a. The DPIP was too pale at the beginning of the experiment. b. The chloroplast solution was too concentrated. c. The experimenter used chloroplasts that were damaged and could not respond to light. d. The blank was not properly used to calibrate the colorimeter.
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C--since that would result in no response, but the solution would still be lower in transmittance because of the DPIP. a is wrong, since the transmittance level should go up no matter what it starts at. b. If the chloroplasts were more concentrated, then there would be a bigger reaction rather than none. d. is wrong since the blank calibration would just result in a higher or lower starting point, not no reaction.
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Pigments A, B, and C are found in a new species of plant leaf. The pigments are separated by paper chromatography using a polar, hydrophilic solvent. The results are shown in the table below. State the order the pigments would appear on the chromatography paper from the least distance traveled to furthest. State and explain two reasons for the order of pigment migration.
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ORDER: (least) B → A → C (farthest) Pigment(s) with a large molecular mass do not move as far as the pigment(s) with small molecular mass. Pigments with hydrophilic (polar) functional groups move farther up the chromatography paper because they are very soluble in the solvent due to the presence of polar functional groups (carbonyl, carboxyl, hydroxyl).
