Ap Biology Lab 4: Plant Pigments and Photosynthesis

AP BIOLOGY LAB 4: PLANT PIGMENTS AND PHOTOSYNTHESIS

Go to Then click on lab bench. Then click on lab 4.

Go to lab 4a: chromatography and follow the lab along. Answer the following questions.

1. Explain what chromatography is.

2. What is paper chromatography?

3. How does paper chromatography work?

4. Name the pigment that we would expect to see near the solvent front and explain why it moves so quickly.

5. Which pigment would be nearer the middle of a chromatography paper and why?

6. Which pigment would be nearer the bottom of a chromatography paper and why?

Now watch the pigment separation. Draw and label what you see. Look at the molecular structures of the pigments.

7. What is the purpose of the chlorophyll a molecule in the plant?

8. What is the role of the other pigments?

9. Write a formula for determining the reference front of a pigment.

Do analysisI. Write the answer here ______.

Go to lab 4b: plant photosynthesis and follow the lab along. Answer the following questions.

10. Which has more energy, short or long electromagnetic waves?

11. Briefly outline the steps that usually occur when light is absorbed by the pigments of an intact leaf.

12. What is DPIP?

13. If DPIP is a blue color, has light been absorbed by the chlorophyll?

14. What instrument will be used to measure the transmittance of light so that we can measure the amount of photosynthesis occurring?

15. Do you expect to see more of less transmittance of light if photosynthesis is actually occurring?

16. Four cuvettes will be used in this experiment. What is the purpose of tube 1? Tube 2? Tube 3? Tube 4?

17. What is the purpose of the water flask?

18. How should the cuvettes be handled and why is this necessary?

19. Why do we need to prevent light from entering one of the cuvettes?

20. Which cuvette do you expect to end up with the lighter color, the one that has boiled chloroplasts or the one with unboiled chloroplasts?

For analysis of results II, use the following information and you can make one graph with 4 distinct lines.

Time (min)
Cuvette / 0 / 5 / 10 / 15
unboiled/dark / 31.3 / 32.5 / 35.5 / 34.8
unboiled/light / 32.7 / 24.5 / 63.7 / 65.1
boiled/light / 32.7 / 32.9 / 33.1 / 32.5
no chloroplasts/light / 31.3 / 31.3 / 31.3 / 31.3

Analysis:

21. What is the function of DPIP in this experiment?

22. What molecule found in chloroplasts does DPIP “replace” in this experiment?

23. What is the source of electrons that will reduce DPIP?

24. What was measured with the spectrophotometer in this experiment?

25. What is the effect of darkness on the reduction of DPIP? Explain.

26. What is the effect of boiling the chloroplasts on the subsequent reduction of DPIP? Explain.

27. What reason can you give for the difference in the percentage of transmittance between the live chloroplast that were incubated in the light and those that were kept in the dark?

28. During summer, leaves are generally bright green. What would you hypothesize that this indicates about the role of green light wavelengths, chlorophyll, and the photosynthetic process?

29. Why do leaves turn colors other than green in autumn?

30. Where do these other colors come from?

31. How do trees/plants prepare for winter?

32. Design a controlled experiment to test the effect of some variable factor on photosynthesis. Use separate paper of needed.