Lab Practical #2 Practice Qs

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2. Which of the following wavelength settings is best for having a Spec 20 detect the absorbance of light by a substance that is blue in solution? A. 600. B. 425. C. 450. D. 475. E. 400.

A. 600. Explanation: Blue solutions strongly absorb light in the red region (~600nm) of the visible spectrum.

13. In the oxygen production lab, what compensation was made for the heat generated by the lamps? A. A tank of water was placed in the light path to absorb heat. B. An amount was subtracted from each oxygen production rate to account for temperature effects. C. A heat-resistant strain of Chlorella was used. D. All of the above represent means that were used to compensate for the heat. E. Only A and B above were used to compensate for the heat.

A. A tank of water was placed in the light path to absorb heat.

11. Which of the following is/are true of the solubilities of the pigments studied in lab? A. Carotene is more soluble in ethanol than in petroleum ether. B. Chlorophyll a is more soluble in methanol than in petroleum ether. C. Chlorophyll b is more soluble in petroleum ether than in methanol. D. All of the above are true concerning the pigments studied in lab. E. Only B and C are true of the pigment solubilities.

A. Carotene is more soluble in ethanol than in petroleum ether.

10. Which of the following is done to determine the absorption spectrum of a substance? A. Measure its absorbance over a range of different wavelengths of light. B. Plot the rate of absorbance change versus time. C. Measure its absorbance at one wavelength over time as the substance is reduced. D. Measure its absorbance at one wavelength over time as the substance is oxidized. E. Subtract the absorbance of the substance when it is reduced from the absorbance of the substance when it is oxidized.

A.Measure its absorbance over a range of different wavelengths of light.

12. In the oxygen production lab, how was PFR varied? A. The PFR was varied by adjusting the offset control on the amplifier. B. The PFR was varied by adjusting the distance between the light source and the tube containing Chlorella. C. The PFR was varied by adjusting the color of the light source. D. The PFR was varied by moving the light source. E. The PFR was varied by adjusting the temperature of the light source.

B. The PFR was varied by adjusting the distance between the light source and the tube containing Chlorella.

1. In the oxidation of water lab that utilized the blue dye DPIP, which of the following represents a measured (dependent) variable? A. Light intensity. B. pH. C. Change in absorbance over time. D. Wavelength of light. E. Temperature.

C. Change in absorbance over time. Explanation: You measured the loss of blue color (i.e., the reduction of DPIP) by noting the change in absorbance over time.

3. Which of the following do chloroplasts and sodium bisulfite hold in common? A. Sodium bisulfite may break down into DPIP and chloroplasts may produce DPIP. In either case the DPIP produced may oxidize water. B. Sodium bisulfite may break down into DPIP and chloroplasts may produce DPIP. In either case the DPIP produced may reduce water. C. Sodium bisulfite and chloroplasts may cause DPIP that is initially blue in solution to become colorless. D. Sodium bisulfite and chloroplasts may cause DPIP that is initially colorless in solution to become blue. E. Sodium bisulfite and chloroplasts both may oxidize water by adding electrons to the water.

C. Sodium bisulfite and chloroplasts may cause DPIP that is initially blue in solution to become colorless. Explanation: Both sodium bisulfite and chloroplasts may reduce DPIP. DPIP looses its color when it becomes reduced.

9. The absorption spectrum of carotenes as determined in lab sometimes showed an absorption peak in the red region of the spectrum. However, the absorption spectrum of carotenes shown in the textbook did not show such a peak. What caused this difference? A. Hot ethanol was used to extract pigments in our lab; the extraction procedure outlined in the textbook used cold ethanol. B. The spinach used in lab was briefly boiled in water; the procedure outlined in the textbook did not use boiling water. C. The carotenes extracted in our lab were contaminated with chlorophyll; the carotenes used in the textbook were not contaminated with chlorophyll. D. The spectrophotometer used in our lab was able to emit light in the red region of the spectrum; the one used in the textbook could not. E. In our lab we used the proper amount of carotenes; in the textbook the amount of carotenes was inadequate to measure absorption in the red region.

C. The carotenes extracted in our lab were contaminated with chlorophyll; the carotenes used in the textbook were not contaminated with chlorophyll.

6. The reduction of DPIP by chloroplasts was coupled to which reaction below? A. The oxidation of carbon dioxide. B. The oxidation of oxygen. C. The oxidation of water. D. The oxidation of NADPox. E. The oxidation of sodium bisulfite.

C. The oxidation of water. Explanation: When water is oxidized in photosynthesis it looses electrons. Those electrons are available to reduce DPIP.

4. Which of the following exercises that you performed in lab best shows that chloroplasts play a crucial role in the color change of DPIP? A. Determining the difference in the absorption spectra of chlorophylls a and b that were removed from chloroplasts by boiling ethanol. B. Comparing the change in absorbance of an illuminated tube completely covered with aluminum foil with the change in absorbance in an identical illuminated tube that was not covered with foil. C. Checking the absorption spectra of oxidized versus reduced DPIP. D. Comparing the absorbance changes in separate tubes in which increasing amounts of chloroplasts were added. E. Determining the difference in the absorption spectra of chlorophyll a and carotenoids that were removed from chloroplasts by boiling ethanol.

D. Comparing the absorbance changes in separate tubes in which increasing amounts of chloroplasts were added. Explanation: Showing that increasing amounts of chloroplasts increase the rate of DPIP reduction provides evidence that chloroplasts are the active ingredient in this experiment.

5. What was the purpose of using a buffer for the isolation and function assessment of chloroplasts? A. The buffer maintained a constant temperature in the chloroplast preparation; this was necessary because the lights used in the experiment produced heat. B. To maintain a constant amount of light (about 500 foot-candles) in the chloroplast preparation. C. To maintain a constant amount of carbon dioxide in the chloroplast preparation. D. To eliminate pH as a variable in the experiment. E. To maintain a constant amount of oxygen in the chloroplast preparation.

D. To eliminate pH as a variable in the experiment. Explanation: The buffer maintained constant pH.

7. Which of the following are capable of reducing DPIPox? A. Sodium bisulfite. B. Illuminated chloroplasts. C. Potassium Chloride (KCl) D. All of the above. E. Only A and B above.

E. Only A and B above.

8. Which of the following is/are true of the absorption spectrum of chlorophyll b as studied in lab? A. Chlorophyll b had an absorption peak at about 550 nm. B. Chlorophyll b had an absorption peak at about 640 nm. C. Chlorophyll b had an absorption peak at about at about 460 nm. D. All of the above are true of the chlorophyll b absorption spectrum. E. Only B and C are true of the absorption spectrum of chlorophyll b.

E. Only B and C are true of the absorption spectrum of chlorophyll b.