13.3: Lab Report
Exercise 1 Data:
Make a sketch of your chromatogram using the template that follows. Using colored pencils, note the color of the bands. Use Table 1 to help you identify each pigment. On your sketch, label each band with the name of the pigment. Mark the distance (in cm) from the initial pigment band to each colored band as well as the total distance from the initial pigment band to the solvent front.
Sketch of Resulting Chromatogram
- Use the data from your sketch to complete the data table below.
- Calculate the value and include that in your data table.
|
A |
B |
C |
D |
E |
|---|---|---|---|---|
|
Name of Pigment |
Description of color |
Distance solvent front traveled from initial pigment band |
Distance pigment traveled from initial pigment band |
Rf value of pigment (column D / column C) |
Exercise 1 Review Questions:
- Which plant pigments are most polar?
- Which are least polar?
- How do these differences in polarity affect the movement of the pigments up the chromatography paper? Explain why this is observed.
4. What does the abbreviation Rf stand for? How is it calculated? What does it tell us?
- If Solution A moves 4 cm and Solution B moves 4.5 cm on a piece of chromatography paper, when the solvent moves 10 cm, which is the most polar solution? Explain your answer.
Exercise 2 Data and Review Questions:
|
Pigment |
Peak Absorption Wavelengths (nm) |
Sample 1 |
Sample 2 |
Sample 3 |
|---|---|---|---|---|
|
Chlorophyll A |
430 and 662 |
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Chlorophyll B |
453-642 |
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Carotenoids |
460-550 |
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Anthocyanins |
520* |
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Xanthophyll |
494 |
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Betalains |
535 or 480* |
*peaks may vary and are pH-dependent.
- How do you think the knowledge obtained from your chromatogram and the spectrograms relate to our understanding of plant pigments?
- Why do leaves change color in the fall?
Exercise 3 Employing Steps in the Scientific Method:
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Record a Hypothesis for the question stated above. ________________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
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Minute |
In Water/Detergent |
In Bicarbonate/Detergent |
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1 |
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2 |
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3 |
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4 |
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5 |
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6 |
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7 |
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8 |
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9 |
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10 |
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11 |
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12 |
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13 |
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14 |
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15 |
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16 |
Exercise 3 Review Questions:
- Complete the following sentence.
Photosynthesis is a set of ____________________________ in which ____________energy is converted to __________________energy.
- Why do some trees appear green in the summer but change colors in the fall?
3. What optimal wavelengths (or peaks) did you observe for both chlorophyll a and b ?
4. Do your leaf disks float? Use the information in this diagram of a cross-section of a leaf to explain why a leaf disk would float.
- Where does photosynthesis occur in a leaf? State which organelles carry out photosynthesis and which type or types of leaf cells have this organelle.
- Explain why it is useful to the plant to have air spaces around the spongy mesophyll cells in the leaves. (Hint: Recall the chemical equation for photosynthesis.)
- What was the purpose of the sodium bicarbonate in this experiment?
- Leaf disks normally float. What caused the leaf disks to sink?
- To measure the rate of photosynthesis, you replaced the air in the spongy mesophyll in your leaf disks with a liquid. This caused the leaf disks to sink. Then you put these leaf disks in water with dissolved CO2 and measured the amount of time it took for the leaf disks to float. Which product of photosynthesis accumulated in the spongy mesophyll and caused the leaf disks to float?
- Suppose that a leaf disk that has had the air sucked out is placed in a bicarbonate solution under a dim light that results in a low rate of photosynthesis that just equals the rate of cellular respiration. Would you expect this leaf disk to float? Explain why or why not.
Exercise 4: Observing and Quantifying Stomata (Optional)
- Record the Question that is being investigated in this experiment. ________________________________________________________________
- Develop a hypothesis about the number of open stomata found on the upper side of a leaf as compared to the lower side of the leaf. ___________________________________________________________
- Develop a hypothesis about the number of open stomata found on the upper side of a leaf as compared to the lower side of the leaf. Write your hypothesis in the space below. ____________________________________________________________
- Predict the results of the experiment based on your hypothesis (if/then). ________________________________________________________________
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Surface of Leaf |
# of Stomata: View 1 |
# of Stomata: View 2 |
# of Stomata: View 3 |
Average # of Stomata |
|---|---|---|---|---|
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Upper |
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Lower |
Extension Activity: (Optional)
The results of this experiment can be presented graphically. The presentation of your data in a graph will assist you in interpreting your results. Based on your results, you can complete the final step of scientific investigation, in which you must be able to propose a logical argument that either allows you to support or reject your initial hypothesis.
- Graph your results using the data from Table 3.
- What is the dependent variable? Which axis is used to graph this data? ______________________________________________________________________
- What is your independent variable? Which axis is used to graph this data? _____________________________________________________________________
Exercise 4 Review Questions:
- What are stomata?
2. What is the importance of stomata in photosynthesis?
3. What is the function of the guard cells?
4. During the lab activity, were more stomata observed on the upper surface of the leaf or the lower surface of the leaf? Explain why you think this distribution exists.