# Spinach Photosynthesis Lab Report

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Spinach Photosynthesis Lab Report
BIOLOGY DCN PHOTOSYNTHESIS LAB # 6
Effect of varying coloured filters on the photosynthetic rate of spinach chloroplasts
The data below is just representative of what trends and relationships you were supposed to see.
Numbers can vary.
Absorbance at 620 nm for each treatment
DCPIP + chloroplasts t=0 min.
0.93
0.945
0.905
0.915

t=3 min.
0.95
0.731
0.83
0.816

change in
A620
-0.02
0.214
0.075
0.099

t=0 min.

t=3 min.

change in
A620

t=0 min.

t=3 min.

change in
A620

0.632
0.636
0.636

0.628
0.63
0.634

0.004
0.006
0.002

0.476
0.416
0.422

0.478
0.417
0.44

-0.002
-0.001
-0.008

Filter Colour
Blue
Green
Red

2

DCPIP+ 5ml of sorbitol

Corrected change in A620
0.212
These rates correspond to the wavelengths of light that are absorbed by the chloroplasts in the presence of the differently coloured filters.
Questions:
1. What is the independent variable for Part A of the exercise? What is the dependent variable in Part A of this exercise?
Independent variable = wavelength
Dependent variable = absorbance
2. What is the independent variable for Part B of the exercise? What is the dependent variable in Part B of this exercise?
Independent variable = wavelength of light transmitted in the presence of differently coloured filters
Dependent variable = rate of photosynthesis measured by the rate of reduction of the dye DCPIP
3. In Part B, you varied the distance between the flood lamp and the test tube, depending on the filter being used. Why was this manipulation done? Explain the relevance of this manipulation in terms of experimental design and the scientific method.
In a correctly designed experiment all variables, except one, have to be constant. The distance between the flood lamp and the experimental test tube affects the intensity of light. This distance was varied when using different coloured filters to ensure that
The wavelengths of light preferred by this plant are about 550 nm and above. We see wavelengths of light that are transmitted or reflected, but not what is absorbed by the plant. From the graph we can conclude that wavelengths from 450 – 500 nm are not absorbed. The colour of the plant therefore is blue-green.

5. In Part B, you indirectly measured photosynthetic rate under 10 different conditions (see
DCPIP + chloroplasts in the presence of a blue filter and light should give the highest rate of NADPH production. NADPH is produced during the light reaction (non-cyclic photophosphorylation). Since the rate of DCPIP reduction, highest in the presence of the blue filter, indirectly indicates the rate of electron transfer during the light reaction
(see Figure 6–1), the faster the rate of DCPIP reduction reflects the faster transfer of electrons from water to NADP+ and the transfer of 2H+ + 2 electrons from water to

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