Lab 4: Photosynthesis
AP Biology
2004-2005
Lab 4: Photosynthesis
Description
determine rate of photosynthesis under
different conditions
light vs. dark
boiled vs. unboiled chloroplasts
chloroplasts vs. no chloroplasts
use DPIP in place of NADP+
DPIPox = blue
DPIPred = clear
AP Biology
measure light transmittance
paper chromatography to
separate plant pigments
2004-2005
Lab 4: Photosynthesis
Concepts
photosynthesis
Photosystem 1
NADPH
chlorophylls & other
plant pigments
AP Biology
chlorophyll a
chlorophyll b
xanthophylls
carotenoids
experimental design
control vs. experimental
2004-2005
Lab 4: Photosynthesis
Conclusions
Pigments
pigments move at different rates based on
solubility in solvent
Photosynthesis
light & unboiled
chloroplasts
produced
highest rate of
photosynthesis
AP Biology
Which
is the control? #2 (DPIP + chloroplasts + light)
2004-2005
Assessment Questions
1. Which pigment migrated the farthest? Why?
2.
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?
3.
Design an experiment to test your hypothesis from the
question above. Describe your experiment or draw a picture of
your experimental setup. If you draw your setup, be sure to
label each component and its purpose.
AP Biology
2004-2005
4. Why do leaves change color in autumn?
5. What is the function of the chlorophylls in photosynthesis
6. What are the accessory pigments and what are their functions?
AP Biology
2004-2005
7. In your experiment you used paper chromatography to separate
various pigment molecules. There are several other
chromatographic techniques employed to separate a variety of
molecules. Research another form of chromatography and
describe it below.
8. What does the Rf value represent? If you were to perform your
experiment on a chromatography strip what was twice the length
of the one you used, would your Rf values still be the same?
AP Biology
2004-2005
9. Shown below is a strip of chromatography paper and a list of five
molecules and their Rf values. Assuming the solvent front traveled
54mm, place each molecule where it would be found on the finished
chromatogram.
10. What is the absorption spectrum?
11. In what way is the spectrophotometer used to measure the rate of
photosynthesis?
12. Below is a graphic representing the steps in the process of
photosynthesis. Place the components from the list into their proper
place on the graphic.
AP Biology
2004-2005
Lab 4: Photosynthesis
ESSAY 2004 (part 1)
A controlled experiment was conducted to analyze the effects of darkness and
boiling on the photosynthetic rate of incubated chloroplast suspensions. The dye
reduction technique was used. Each chloroplast suspension was mixed with
DPIP, an electron acceptor that changes from blue to clear when it is reduced.
Each sample was placed individually in a spectrophotometer and the percent
transmittance was recorded. The three samples used were prepared as follows.
Sample 1 — chloroplast suspension + DPIP
Sample 2 — chloroplast suspension surrounded by foil wrap to provide a
dark environment + DPIP
Sample 3 — chloroplast suspension that has been boiled + DPIP
Data are given in the table on the next page.
a. Construct and label a graph showing the results for the three samples.
b. Identify and explain the control or controls for this experiment.
c. The differences in the curves of the graphed data indicate that there were
differences in the number of electrons produced in the three samples during
the experiment. Discuss how electrons are generated in photosynthesis and
why the three samples gave different transmittance results.
AP Biology
2004-2005
Lab 4: Photosynthesis
ESSAY 2004 (part 2)
Time
(min)
AP Biology
Light, Unboiled
Dark, Unboiled
% transmittance % transmittance
Sample 1
Sample 2
Light, Boiled
% transmittance
Sample 3
0
28.8
29.2
28.8
5
48.7
30.1
29.2
10
57.8
31.2
29.4
15
62.5
32.4
28.7
20
66.7
31.8
28.5
2004-2005