Photosynthesis and Respiration Under Filtered Light
CU Boulder, Fall 2007
Do the rate
s of photosynthesis change when Juniper sprigs are
placed under red and blue light filters?
Even though red light has a lower energy compared with blue light, blue light can be
damaging to a plant and, therefore, may be filtered by the plant to protect
itself. In "light" of
this, I hypothesized that photosynthesis rates will be highest under red filters,
as the plant would be able to absorb all of the red wavelengths safely whereas the plant may be
filtering some of the damaging blue wavelengths.
this hypothesis , data needed to be
collected from the control
variable (Juniper sprigs under normal white light). The
experiment consisted of Juniper sprigs placed into a chamber with a CO2 gas
sensor attached. The CO2 gas probe
attached to the computer
to record the rate of change of CO2 in light versus dark to estimate the rate of
water bottle was placed on top of the chamber to provide a heat sink. High-intensity, full-spectrum lights
were directed at the Juniper sprigs for 10 minutes,
then the lights were turned off and the chamber was wrapped in tin foil for 10 minutes of darkness. Another 10 minutes under the lights was sufficient to
collect data for normal white light .
To test photosynthesis
rates of red and blue light, the above methods were followed with the addition
of alternating red and then blue filters placed around the chamber holding the
Juniper sprigs. Data was recorded
for sprigs under the
light with each filter for 7 minutes then in the dark for 7 minutes, repeating
each test cycle three times for an average [NG2] .
to the means[NG3], photosynthesis rates were higher under red
NOT significant (p-value=0.1145); however, the
difference in respiration rates between
red and blue light filters WAS significant[NG4] (p-value=0.035).
under blue light filters were breaking down the sunlight and making sugars at such a high rate
that photosynthesis rates under this filter
was masked by high respiration rates. I, therefore, have to reject my hypothesis.
Experimental methods which could potentially lead to errors in data collection: time switched from light to dark was not always exact; amount of air fanned in the chamber between testing; amount of Juniper sprigs used; possible holes in the filters or not complete darkness allowing white light to leak in; lights not set in exact same place each time; and the filters used may not have represented the exact red and blue wavelengths of natural light.
findings are consistent with the alternative hypothesis that photosynthesis
rates will be the highest under blue light filters. This modified hypothesis is also
supported by Cusack et al. 2006.