The Effect of Constant Darkness on Chlorophyll Concentration in Pelargonium spp Plants
Amber Arvizu and Madison Dixson
Department of Biological Sciences
Saddleback College
Mission Viejo, California 92692
Chlorophyll, a green pigment found within plant leaves, is the compound that allows
for the capture of light used in photosynthesis. Since chlorophyll is integral to the process
of photosynthesis it was hypothesized that it would differ in the leaves of light and dark
adapted plants. In this experiment chlorophyll was extracted from leaf samples and its
concentration was determined using spectrophotometric methods. Student groups from
Saddleback Community College, Mission Viejo, California Biology 3B morning and
afternoon lab punched out 12 leaf discs measuring 6.1mm. Six leaf discs from a hybrid
geranium (Pelargonium x hortorum) plant that was held in the dark for 3 days and the 6
leaf discs where from the leaves of the same species plant that was held in the light for three
days. Six vials where then filled with 5ml of 80% acetone. Two leaf discs from the same
sample plant were added to each vial. The vials where refrigerated at 4°C for 48 hours.
The chlorophyll concentration in the supernatant acetone was determined using the
method of McKinney (1941) using a Beckman DU 700 spectrophotometer. Concentration
per volume was converted to concentration per square millimeter. A total of 57 light and 57
dark samples were analyzed. A two-tailed unpaired t-test yielded a p value of 0.16.
Although it was hypothesized that plants would produce differing amounts of chlorophyll
under different lighting conditions, the data did not support this. Since photosynthesis
relies so heavily upon chlorophyll concentration, it seems hard to justify this conclusion.
Perhaps there are species specific responses to lighting conditions; or perhaps it takes more
than three days for the plant to respond to the lighting condition.
Concentration of chlorophyll
(ug/mm2)
0.33
0.32
0.31
0.3
0.29
0.28
0.27
0.26
0.25
Light
Dark
Time of Day
Figure 1. Mean comparison of chlorophyll concentration from plants held in the dark and in the light for 3 days.
There was no significant difference between chlorophyll concentration (ug/mm2) of plants held in the dark versus
the plants held in the light (p = 0.16). Error bars indicate 95% confidence intervals.