FREE ESSAY ON PHOTOSYNTHESIS

PHOTOSYNTHESIS

The Effects of Various Wavelengths on Photosynthetic Rate
INTRODUCTION
Photosynthesis is the process by which autotrophic organisms convert light
energy to chemical energy in the form of glucose [1]. Without this process life on earth
would be very different because every organism directly or indirectly depends on
photosynthesis. Because plants are at the bottom of the food chain they must create
their own energy; this is done through photosynthesis. Various pigments located
through out the leaves and stems of plants called chlorophylls absorb wavelengths from
sunlight. They absorb all wavelengths of natural light (400-700 nanometers), except
those between 525-550 nm which are reflected giving plants their green color [2]. 
The question of this experiment is how do different wavelengths effect
photosynthetic rate? The purpose of this experiment was to decide if blue light
(wavelengths of 425-475 nm) or red light (wavelengths of 650-700 nm) would produce
an increase in photosynthetic rate when compared to natural/white light (wavelengths of
400-700 nm). The hypothesis stated that the blue light would result in a higher
photosynthetic rate than the red light but both would be less than the control which was
white light. The rationale for this hypothesis is best depicted by Figure 1, which shows
the various types of chlorophylls and the wavelengths that they absorb [3]. It appears
that more absorption occurs around blue light than that of red light. 
Due to classroom restrictions artificial light was used to conduct the experiment.
The classroom was necessary because a carbon dioxide sensor and computer were
used to calculate photosynthetic rate.
This research could be important if the results show outstanding increases in
photosynthetic rate. World Hunger is a major concern if a process could be found
through which photosynthetic rate is maximized perhaps food production could be
maximized as well and hungry mouths may be fed.
EXPERIMENTAL DESIGN
The apparatus used to conduct this experiment is shown in Figure 2. The fish
bowl filled with water was used to absorb the heat given off by the lamp and prevent
damage to the plant. Water was placed in the dish containing the plant to create an air
tight seal to prevent more CO2 to enter the system. The sensor used detects the
concentration of CO2 in parts per million. Three rye grass plants were used in rotation
to give each plant a rest from photosynthesizing, when not in use the plants were kept
in the dark. Colored cellophane (red or blue) was wrapped around the soda bottle in
which the plant is enclosed to allow only that specific color to reach the plant. The
control used was clear cellophane. The computer does most of the work, plotting the
CO2 depletion rate with the use of the CO2 sensor and the Logger Pro software. Each
experimental group (of which there were two: red and blue) and control group ran for
ten minutes with three replicates of each. The photosynthetic rate was then calculated
by dividing the CO2 depletion rate (slope of the line graphed by the computer) by the
mass of the plant. Data was then statistically analyzed through t-tests performed using
Primer of Biostatistics.
RESULTS
The results of the experiment are all over the charts with the control group
having a standard deviation of 8.248, this is extremely high and due to one control
replicate being almost double the value of another replicate. The two experimental
groups had lower standard deviations; red= 2.836 and blue= 0.8759. 
The average values of the replicates of the control and experimental groups is
located in figure 3, which also shows the standard deviation. While both experimental
groups have a smaller rate than the control, the difference between the two
experimental groups is almost nonexistent. 
DISCUSSION
The statistical data does not support the hypothesis. This is because there is not
a significant difference between the sets of data. The blue light and red light results
were almost the same with a difference of only 0.25 (ppmCO2/min)/g. It appears that
there is a more significant difference between the experimental groups and the control.
With the control averaging almost 5 (ppmCO2/min)/g above the experimental groups
but due to the variation between the replicates of the control ( with the highest being
25.56 (ppmCO2/min)/g and the lowest being 9.89 (ppmCO2/min)/g) the statistically
results showed too much variation within one group for solid conclusion. Because the
data did not distinguish any differences between the groups there is no relevance to
this particular experiment. 
Another group performed a similar experiment in which they tested yellow and
blue light and compared the results to their control which was clear. They hypothesized 
that the yellow would have a lower absorption than the clear but a higher absorption
than the blue. Their results statistically supported that the blue was lower than the
yellow but did not support that the yellow was lower than the clear. 
Many possibilities could have produced this short coming. The one that stands
out most is the fact that three different plants were used and each plant probably had
its own rate at which it liked to photosynthesize. This could be fixed if one plant were
used but this was not realistic because the plant would have had to receive a certain
period of rest between each run, due to time constraints this was not possible. The
results also may have been different if natural sunlight was used in place of artificial
light, but due to classroom restraints this also was not possible. So using just one
plant
with more time involved or the use of sunlight instead of artificial light are two
alternative
methods for testing the hypothesis. A new direction of this experiment could look more
closely at specific pigments of the plant and use a combination of different pigments to
maximize photosynthetic rate using a wavelength absorbed by those pigments.
RESOURCES
1. Hirrel, Marc. "Investigations of Photosynthesis." Biol 1440 Principles of Biology I
Homepage. *http://faculty.uca.edu/marc.hirrel/bio1/photosynI_t2k.htm*
2. "Photosynthesis."
*http://gened.emc.maricopa.edu/Bio/bio181/BIOBK/BioBookPS.htm*
3. Campbell, Neil. Biology 5th ed. Addison Wesley Longman, Inc. New York. 
Chapter 10. p. 168-187.