Rate of Photosynthesis
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Rate of Photosynthesis
by
Natalie Moses
Biology 105: Section 1
Mr. Scot Eichorst
21 October 2013
Rate of Photosynthesis
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Introduction
Photosynthesis converts light energy into chemical energy through a complex
chemical process that practically all life depends on for food and oxygen (Vodopich &
Moore, 2014, p. 137). This process is summarized by the equation: carbon dioxide
(6CO2) + water (12 H2O)sugar (C6H12O6) + water (6 H2O) + oxygen (6O2) (Raven et
al., 2014, p. 148). Although in animals oxygen is transported through the circulatory
system and diffusion, plants lack an active transport system for oxygen (Nowak & Hietz,
2010, p. 101-02). Therefore oxygen is then released freely into the environment, and
sugar is used as energy. With oxygen being an important byproduct of photosynthesis,
knowledge of the “production, consumption, and homeostasis” of this oxygen is a
“primary research goal in biology and biotechnology” (Tschiersch et al., 2012, p. 926).
Leaf disks normally float in solution because of the presence of oxygen. However,
when the disks are degassed they become denser and therefore sink. The solution of
NaHCO3 acts as a source of carbon for the process of photosynthesis to occur. As
photosynthesis progresses oxygen is released and the consistency of the leaf disks
change, causing them to float. At the same time, cellular respiration is occurring and
consuming oxygen. This makes the rate of the disks raising an indirect measure of
photosynthesis occurring in the solution (“Photosynthesis Lab,” 2013). Water is used as a
control in multiple experiments because it does not produce a source of carbon and
therefore photosynthesis should not occur.
There are some procedures used in the experiments to make them occur more
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accurately and efficiently. One of those is the addition of dilute liquid soap to the
solutions of NaHCO3 and H2O. This is done because the soap adds the ability of the
solution to be drawn into the leaf through the hydrophobic surface more easily
(“Photosynthesis Lab,” 2013). To obtain the leaf disks that are used for every experiment,
a cork borer is pressed down onto spinach leaves to produce individual leaf disks. Each
disk must be degassed to remove any oxygen already present in the disk. Creating a
vacuum affect in a syringe barrel does this. While doing this, NaHCO3 will “infiltrate the
spaces evacuated by the oxygen,” (“Photosynthesis Lab,” 2013). The presence of
NaHCO3 will serve as a source of carbon dioxide needed for photosynthesis.
Three different experiments were performed to test the ability of photosynthesis
to occur in various situations. The first experiment, used to supply background
information, was to describe the affect presence or absence of light has on solutions of
H2O or NaHCO3 (“Photosynthesis Lab,” 2013). The affect light has on the process of
photosynthesis could vary in a few different ways. The presence of light on NaHCO3
solution could cause photosynthesis to happen in the leaf disks. The absence of light on
NaHCO3 solution could cause photosynthesis to occur in the leaf disks. The presence or
absence of light on NaHCO3 solution could have no affect on the rate of photosynthesis in
the leaf disks. These hypotheses can be measured due to the presence of H2O acting as a
control.
The second experiment was to test how the wavelength of light affected the
production of oxygen during photosynthesis (“Photosynthesis Lab,” 2013). The affect of
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gel filter color on the rate of photosynthesis could vary in a few different ways. The
presence of a filter could increase the rate of photosynthesis in the leaf disks in the
solution of NaHCO3. The presence of a filter could also decrease the rate of
photosynthesis in the leaf disks in the solution of NaHCO3. The presence of a filter could
have no affect on the rate of photosynthesis. With these hypotheses are further
investigations on whether different colors of filters have an affect on the rate of
photosynthesis. The last hypothesis can be observed by the control, which is a clear
filter.
The final experiment performed was to test the affect of light bulb type on the
production of oxygen during photosynthesis (“Photosynthesis Lab,” 2013). This was
tested by the use of a 15- and 60-watt soft white, incandescent bulb on leaf disks in a
solution of NaHCO3 and separately in a solution of H2O. The 15-watt bulb could
increase, or decrease, the rate of photosynthesis on the leaf disks. The 60-watt bulb also
has the potential to increase, or decrease, the rate of photosynthesis on the leaf disks. The
different types of bulbs may have no affect on the rate of photosynthesis (no change).
These previously stated hypotheses will be able to be measure by the observation
and recording of the number of floating leaf disks at one minute intervals for twenty
minutes. The floating of a leaf disk means that oxygen was produced and therefore
photosynthesis is taking place. The more leaf disks that float faster means that the rate of
photosynthesis has increased. The first experiment will be used as reference information
to be able to compare the rate of photosynthesis occurring.
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Materials and Methods
Before the experiments began, sodium bicarbonate was prepared. The solution
consisted of 0.1 moles of sodium bicarbonate dissolved in 1 liter of distilled water. One
drop of dilute liquid soap was also added for every 500 mL of NaHCO3 solution. This
solution was used for all experiments. Three experiments were performed in order to test
different variables against the rate of photosynthesis.
The first experiment was done to compare the differences in light and dark
environments and the differences of solutions of H2O and NaHCO3. Three hundred mL of
NaHCO3 solution and 300 mL of DI water solution were obtained in beakers labeled to
note which solution was which. Next, four plastic cups were labeled A, B, C, and D. Cup
A was to be NaHCO3 in a lighted environment. Cup B was H2O, also in an environment
exposed to light. Cup C contained NaHCO3, but it was not exposed to light. Cup D was
also kept in the dark and contained H2O. Each cup was marked three centimeters from the
bottom to indicate how much solution was to be poured into the cup. Next, the replicates
were prepared. A fresh spinach leaf was placed onto a smooth section of Styrofoam. With
the use of a cork borer, circles were punched out of the leaf. Ten leaf disks were obtained
for each solution. The leaf disks were then degassed and infiltrated with the appropriate
solution. Using a plunger to vacuum the oxygen out of the mesophyll of the leaf did this.
Once the leaves had been completely removed of all oxygen, ten leaf disks were placed
into each appropriate labeled plastic cup along with the correct solution to a depth of
three cm (approximately 100 mL). Cup A contained 100 mL of NaHCO3, ten leaf disks,
and was placed under a 100-watt light bulb. Cup B contained 100 mL of water, ten leaf
disks and was also placed under a 100-watt light bulb. Both cups C and D were placed
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under a cardboard cover to keep them away from any outside light source. Cup C had 100
mL of NaHCO3 with ten leaf disks, and Cup D had 100 mL of water with ten leaf disks.
After the cups were placed in their appropriate positions, timing began. After each minute
interval, each cup was swirled gently. Once the disks had settled back down, the number
of leaf disks that remained floating was recorded. This process continued for twenty
intervals.
The next experiment that was performed was to determine how the wavelength of
light affected the production of oxygen gas during photosynthesis. For this experiment,
four containers were obtained, and all were filled with NaCOH3. The treatments in this
case were the use of filters over the light. A red, green, blue, and clear (constant) filter
was put over their respected containers of 100 mL of NaCOH3 and ten degassed, spinach
leaf disks, all under a 100 watt bulb. The numbers of floating disks were again recorded
at each minute interval for twenty minutes.
The final experiment done was to see if light bulb type affected the production of
oxygen during photosynthesis. Two cups were once again filled with 100 mL of
NaCOH3, and two other cups were filled with 100 mL of H2O. The later two were to act
as controls. All four cups had ten degassed, spinach leaf disks added to them. One
NaCOH3 cup and one water cup were placed under a 60-watt, soft white, incandescent
light bulb. The other two cups were placed under a piece of cardboard with a 15-watt,
soft white, compact fluorescent bulb shining through a hole to keep excess light from
shining on the solutions. Each cup was gently swirled and floating leaf disks were
recorded at minute intervals for twenty minutes.
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Results
The amount of oxygen produced by photosynthesis in spinach leaves was
measured and recorded as tables one, two, and three describe. The oxygen production
was measured by the number of floating leaf disks at each minute interval. As you can
see from the data, oxygen production ranged greatly based on the contents of each
container and the varied types of light available.
Table 1
Number of Floating Leaf Disks at One Minute Intervals in
Light and Dark Conditions (Investigation One)
H2O in
Time (minutes)
NaHCO3 in Light
NaHCO3 in Dark
Light
0
2
0
0
1
2
0
0
2
2
0
0
3
2
0
0
4
5
0
0
5
9
0
0
6
9
0
0
7
9
0
0
8
9
0
0
9
9
0
0
10
9
0
0
11
9
0
0
12
9
0
0
13
9
0
0
14
9
0
0
15
9
0
0
16
9
0
0
17
9
0
0
18
9
0
0
19
9
0
0
20
9
0
0
H2O in
Dark
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Table 1 shows the data collected over 20 minutes for the number of floating leaf disks in their appropriate
solutions.
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Table one describes the relationship between oxygen production and presence or
absence of light. The presence of light with the solution of NaHCO3 produced the
greatest number of floating leaf disks and therefore produced a great deal of oxygen
meaning photosynthesis happened. The remaining solutions, absence of light with
NaHCO3, light with H20, and absence of light with H2O, all had no floating leaf disk and
therefore no production of oxygen.
Table 2
Number of Floating Leaf Disks at One Minute Intervals
in Different Wavelengths of Light
Time
(minutes)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Red
Green
Blue
Clear
0
2
2
2
2
2
2
2
3
3
3
3
3
3
4
5
7
6
6
6
6
0
1
1
2
2
2
2
2
2
2
2
3
3
3
5
5
4
4
4
4
5
0
1
1
1
1
1
1
1
1
2
2
4
4
5
7
8
8
9
9
9
9
0
2
2
2
2
2
2
2
2
3
3
3
3
3
3
4
4
4
4
4
4
Table 2 shows the relationship between floating leaf disks in NaHCO 3 solution affected by
different wavelengths of light.
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Table two describes the relationship between oxygen production (observed by the
number of floating leaf disks) and the presence of a filter, altering the color of light. All
of the filters started off with the production of relatively equal amounts of oxygen
production. The blue filter results show that it gradually increased oxygen production,
ending with a result of nine out of ten leaf disks floating. The green filter also gradually
increased. The red filter also gradually increased, ending with six floating leaf disks. The
clear filter (the constant) gradually increased its oxygen production, resulting in less
floating leaf disks than all of the other filters. There was some leaf disks that were
recorded floating and then ended up sinking back to the bottom of their container.
Table 3
Number of Floating Leaf Disks at One Minute Intervals
for Different Light Bulb Types
Time
15 Watts
15 Watts
60 Watts
60 Watts
(minutes)
NaHCO3
H2O
NaHCO3
H20
0
0
0
0
0
1
0
0
0
0
2
0
0
0
0
3
0
0
1
0
4
0
0
0
0
5
0
0
0
0
6
0
0
0
0
7
0
0
0
0
8
0
0
0
0
9
0
0
0
0
10
0
0
0
0
11
0
0
0
0
12
0
0
0
0
13
0
0
0
0
14
0
0
0
0
15
0
0
0
0
16
0
0
0
0
17
0
0
0
0
18
0
0
0
0
19
0
0
0
0
20
0
0
0
0
Table 3 shows the oxygen production in leaf disks based on different types of light bulbs.
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The results in table three describe the relationship between oxygen production,
represented by floating leaf disks, and different types of light bulbs. Except for one leaf
disk that floated under the 60-watt bulb in NaHCO3 solution and then ended up sinking
again, no leaf disks floated and remained floating for the entire twenty minutes that were
observed and recorded. However, some leaf disks were observed to begin to float and
then sink back down to the bottom instead of remaining floating.
Discussion
These experiments were used to determine the affects of different variables on the
rate of photosynthesis. For the first experiment, it was hypothesized that one of three
things could happen: the presence of light on NaHCO3 solution could cause
photosynthesis to happen in the leaf disks, the absence of light on NaHCO3 solution
could cause photosynthesis to occur in the leaf disks, or the presence or absence of light
on NaHCO3 solution could have no affect on the rate of photosynthesis in the leaf disks.
Of these three hypotheses, the one that was accepted based on the data was that the
presence of light on NaHCO3 increased the rate of photosynthesis. This was the expected
result because for photosynthesis to take place in the natural environment, light energy
must be present. The importance of this is that it is now known what should be present
for photosynthesis to occur in later experiments.
The second experiment also had results that could have been expected. The
hypothesis that was supported was that a filter would increase the rate of photosynthesis
on a solution of NaHCO3. The filter that most increased the rate of photosynthesis was
the blue filter, followed by the green filter, the red filter, and finally the clear filter. The
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reason for the increase in the rate of photosynthesis due to the filter is most likely
explained by the presence of chlorophyll. The chlorophyll acts in capturing the light in
plants. The blue filter caused the chlorophyll to capture the most light the quickest,
followed by the green, then red, and finally the clear filter. Testing different shades of
color (i.e. different shades of blue, green, or red) with stronger lights for longer periods of
time could be done for further investigation. This would make clear the optimum color
filter for the fastest rate of photosynthesis to occur.
The third experiment produced results that supported the hypothesis that the
different types of light bulbs had no affect on the rate of photosynthesis. The results
showed that no photosynthesis took place, however it was evident that multiple leaf disks
would begin floating and then sink again. This showed photosynthesis is happening, just
at a very slow rate and therefore not producing much oxygen. This was most likely
because the bulbs were too weak for photosynthesis to occur quickly and at a level strong
enough to make the leaf disks float. For further investigation, it would be helpful to
continue the process for longer lengths of time to determine if more time was needed for
photosynthesis to occur due to the weak light energy given off by these bulbs. It would
also be interesting to use stronger watt light bulbs at different levels to determine if the
wattage used was simply too weak to make photosynthesis to occur.
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References
Nowak, W.G., & Hietz, P. (2010). An Improved Model for the Diffusion of Oxygen into
Respiring Wood. World Scientific, 19(1), 101-02.
“Photosynthesis Lab”. (2013).
Raven, P.H., Johnson, G.B., Mason, K.A., Losos, J.B., & Singer, S.R. (2014). Biology.
New York, NY: McGraw Hill.
Tschiersch, H., Liebsch, G., Borisjuk, L., Stangelmayer, A., & Rolletschek, H. An
Imaging Method for Oxygen Distribution, Respiration and Photosynthesis at a
Microscopic Level of Resolution. New Phytologist, 196, 926.
Vodopich, D.S., & Moore, R. (2014). Biology Laboratory Manual. New York, NY:
McGraw Hill.