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Photosynthesis and Respiration Experiment

Photosynthesis and Respiration Margaret E. Vorndam, M.S. Version 42-0103-00-01

Lab Report Assistant

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Observations

Data Table 1: Rf Value Comparison for Chlorophyll Pigments

Chlorophyll Pigment

Observed Color

Distance to top of pigment, mm

Other Students’ Rf Average

# of Rf Results Averaged from other Students (N)

Top of Solvent Front

Carotenoids

Xanthophylls

Chlorophyll a

Chlorophyll b

Distance to top of pigment, mm: Measure from where the top of the solvent extract level intersected the paper chromatograph to the topmost level of the color. Then measure this distance to the top of the solvent front and record.

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Photosynthesis and Respiration Experiment

Data Table 3: Gross Photosynthesis in Elodea

Rates Distance of travel, mm Net Photosynthesis Rate over 10 minutes = mm of movement from marked beginning point on bent tube to end point after 10 minutes

Respiration Rate over 10 minutes = mm of movement from marked end point on bent tube toward beginning point after 10 minutes

Gross Photosynthesis over 10 minutes (= mm Net Photosynthesis + mm Respiration)*

Rate of Photosynthesis over one hour (= Gross Photosynthesis ÷ 10 minutes x 60 minutes)

*Was respiration occurring during photosynthesis? Add back the O 2

that was consumed by plant respiration to obtain the total photosynthetic rate.

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Photosynthesis and Respiration Experiment

Data Table 4: Comparison of Photosynthetic Rate

My Photosynthetic Rate Result

Average of Other Students’ Photosynthetic Rate Results

N = (number of data averaged)

Data Table 4: Observation of pH Change in the Oxygen Cycle Contents of Respirometer

Initial Color

0 ,

minutes

Final Color

T 1 , minutes

Total time for color change, T

1 – T

0 , minutes

Elodea, Bromothymol blue solution

Elodea, Bromothymol blue solution in foil

Data Table 5: Comparison of Photosynthetic Rate

My Result: Total time for color

change, T

1 – T

0 , minutes

Average of Other Students’ Results: Total time for color change,

T 1

– T 0 , minutes

N = (number of data averaged)

Elodea, Bromothymol blue solution

Elodea, Bromothymol blue solution in Foil

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Photosynthesis and Respiration Experiment

Exercise 1: Chlorophyll Pigments Results

Rf = distance to top of pigment in mm ÷ distance to top of solvent front.

Rf Average = average of other students’ Rf values, if available.

1. Rf values are calculated ratios of how far a molecule moved up the paper chromatograph as compared to the length of the solvent front. These values are typically equivalent for multiple trials. Calculate your Rf values based on your paper strip results, and record them in Table 1. The Rf value of the solvent front will always = 1.0, since Rf is a ratio.

2. Construct a stacked bar graph to demonstrate how the Rf value and the chlorophyll pigment are related. The y-axis will represent the Rf scale from 0.0 to 1.0. On the bar graph, label the calculated Rf with the name of the associated chlorophyll pigment. When complete, the bar graph should closely resemble the actual chromatograph. Include a stacked bar graph for your results plus another stacked bar graph next to your graph with your classmates’ averaged values.

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Photosynthesis and Respiration Experiment

Questions:

A. Identify the areas of pigments that you observe on the filter paper. Are they located in the order that you expected?

If not, why not?

B. Compare your paper strip results to the results of the radicchio paper strips below. Are the same pigments present in radicchio leaves?

If not, which chlorophyll pigments are missing?

How might you have guessed that this might be the case?

Example of Results Obtained from Radicchio Paper Chromatograph

Radicchio Paper Chromatograph, dried and marked in preparation for Chlorophyll Pigment

Rf determinations

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Photosynthesis and Respiration Experiment

Discussion

A. Was the initial hypothesis supported or refuted? Explain.

B. If you do not see separate bands of color on the filter paper, what might you conclude?

C. What might explain why the separation of the colors occurred?

D. How do your values compare to your classmates’ values for the same pigments on Table 1 and in your graph? If they are not similar, what may be the reason?

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Photosynthesis and Respiration Experiment

Exercise 2: Conversion of Light Energy to Food by Plants Questions

A. What molecule was produced by the Elodea while it was exposed to light?

B. Which organelle(s) in the plant cell is responsible for this reaction?

C. From where was this molecule derived?

D. What was the purpose of the light?

E. What molecule was produced by the Elodea while it was wrapped in aluminum foil?

F. Which organelle was responsible for this reaction?

G. Set up a table similar to Data Table 3: Comparison of Photosynthietic Rate in the Lab Report Assistant section. Compare your Rate of Photosynthesis to the average rates reported by other students in Table 3, if possible. How similar was your result to theirs?

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Photosynthesis and Respiration Experiment

H. Name at least three experimental variables that could explain why your outcome might vary from that of other students or from your own, if you repeated the experiment.

I. How could one determine how much oxygen is produced by the plant in one hour?

1. From geometry, recall that Volume = πr2h, where r = inside radius of a circle, or here the inside of the tube, and h = length of the movement, which means π x radius squared x height. Since the radius is ½ of the inside diameter, this equation is equivalent to = 3.1416 x (inside diameter of the bent tube in mm ÷ 2)2 x height (equivalent to the distance that the solution traveled) = volume in mm3.

2. To convert mm3 volume to uL (typically the volume specification used at this level of measurement), use the conversion factor of 1 mm3 = 1 uL. Do the calculation to determine the volume of oxygen that is produced by the plant in one hour.

3. How long would the plant need to photosynthesize to produce one liter of O 2 ?

Photosynthesis and Respiration Experiment

Discussion

A. Did this experiment support or refute your initial hypothesis. Explain.

B. Chlorophyll gives plant leaves their green color, (or red, in the case of radicchio, since it lacks a pigment that is typically present in green leaves). Research light and color, and hypothesize whether chlorophyll absorbs green light to any appreciable extent. Propose an experiment similar to the one that you just performed that could be used to support your hypothesis.

C. There is current controversy as to whether the atmosphere is warming due to the burning of fossil fuels and the destruction of the rainforests (the Greenhouse Effect). How does photosynthesis and respiration relate to this controversy?

Photosynthesis and Respiration Experiment

D. Why are the tropics particularly important to oxygen production?

Therefore, why should you support actions that reduce the cutting of rainforests?

E. While this exercise has addressed oxygen production, what other important products result from photosynthesis? Hint: Beside the production of oxygen, why are all animals dependent on plants?

Exercise 3: Respiration in Plants Questions

A. Why is the Elodea rinsed in distilled water?

B. What gas did you add to the Bromothymol blue solution?

How do you know? Respiration is our primary form of energy production.

Photosynthesis and Respiration Experiment

C. Why did the color turn more green-yellow or yellow when you breathed into it?

D. Write an equation for the reaction that explains the color change.

E. What color change occurred after you placed the Elodea in the test tube and turned the light source on/off?

F. What gas is produced and responsible for this change?

G. What gas is being removed?

H. What process is occurring in the first trial without the aluminum foil?

I. What did you observe when you repeated the exercise with the test tube containing the Elodea wrapped in aluminum foil?

J. What gas is produced?

What term could be applied to the second trial?

K. Which process took longer?

Why?

Photosynthesis and Respiration Experiment

Discussion

A. How did the time for color change vary between when the Elodea was present in the test tube (trial 1) versus when the Elodea was wrapped in aluminum foil? What might explain this?

B. Why do both plants and animals respire?

Would life in either group be possible without respiration?

C. Was the initial hypothesis supported or refuted? Explain.

D. Heating causes a Bromothymol blue indicator solution to change from yellow to blue very rapidly without a plant present. What explains this reaction? How did you control for heat in this exercise?

Photosynthesis and Respiration Experiment

E. Set up a data table similar to Data Table 5: Comparison of Photosynthetic Rate in the Lab Report Assistant section. Compare your results to those of your classmates, if available, in Table 5. Were your results similar? What trends do you observe between the two trials?

F. Explain why your data may have differed from that of other students. What variables could explain this difference?

G. How would you be able to check to ensure that it was the Elodea plant that facilitated the color change and not some other factor?

H. How do plants, such as Pinedrops, Pterospora andromedea, or the Ghost Plant, Monotropa uniflora, that are not photosynthetic, make their food?

Do they respire?

Laboratory Summary

What have you learned from doing this laboratory?