Alexis Cummings
Eric Northrup
Biology 105
20 Oct. 2014
Photosynthesis Lab Paper
Introduction:
Photosynthesis is an important set of chemical reactions on earth that almost all life
depends on for food and oxygen. Photosynthesis is the process of converting radiant light energy
to chemical energy (sugar). This can be seen in the equation of photosynthesis: 6CO2 + 12H2O
 C6H 12O6 + 6H2O + 6O2 (Vodopich & Moore, 2014). This process occurs in plants and some
algae within the chloroplasts and uses chlorophyll. Most of the process of photosynthesis occurs
in the plant leaves.
Photosynthesis can be divided into two sets of reactions. Light-dependent reactions
within photosynthesis require energy from sunlight to drive its reactions. The reaction takes
place within the thylakoid membrane and converts light energy to chemical energy. After
capturing energy from sunlight, ATP is made and NADP+ is reduced to NADPH (Vodopich &
Moore, 2014). The reaction is practically instantaneous and it splits water to release oxygen,
electrons, and protons. After oxygen is released to the environment, sugar is used to fuel growth
or is stored as starch. Light-independent reactions within photosynthesis can occur in the
absence of light but do not occur exclusively in the dark. The dark reaction takes place in the
stroma within the chloroplast. It occurs slower than light-dependent reactions but is still
extremely fast. ATP and NADPH are used to synthesize organic molecules from inorganic CO2
(Vodopich & Moore, 2014). Light-independent reactions convert carbon dioxide to sugar. In
relation to each other, light dependent reactions help fuel light independent reactions. Light
independent reactions use the energy and electron carriers of light dependent reactions to convert
carbon dioxide into glucose that can be used as energy (Vodopich & Moore, 2014).
Evidence of photosynthetic activity can be obtained within the lab. In the investigation
of testing light (100 W) and dark conditions many observations were made. The time it took for
the disks to float provided an indirect measurement of the rate of photosynthesis. When the air
spaces within the leaf disks were infiltrated with solution, the density of the leaf disk increased
and caused the disk to sink. The infiltration solution contained a small amount of sodium
bicarbonate, which dissociated and formed carbonic acid and served as a carbon source for
photosynthesis. As photosynthesis proceeded, oxygen was released in to the leaf, which caused
the disks to float. Since cellular respiration was occurring at the same time, the rate at which the
disks floated is an indirect measurement of the net rate of photosynthesis.
When observing leaf disks in solutions of NaHCO2 and H2O under specific light sources,
the observation was made that the amount of leaf disks floating after twenty minutes was greater
under the 60 W light bulb than the 15 W light bulb in the NaHCO3 solution. Mougot, Vachoux,
and Tremblin’s (2005) experimental results also show that when under a higher watt light source,
there was an enhancement of marennine production in the diatom Haslea ostearia. After close
observations of leaf disks in NaHCO3 and H2O solutions under 15W and 60W light bulbs were
made, one could hypothesize that light bulb type does not affect the production of O2 during
photosynthesis.
The observation was made that the number of floating leaf discs was the same under the
60W full spectrum light blub as it was under the 60W soft white incandescent light bulb after
twenty minutes in the NaHCO3 solution. Mougot, Vachoux, and Tremblin’s (2005)
experimental results also show that when under a blue colored light source, there was not an
enhancement of marennine production in the diatom Haslea ostearia. After close observations of
leaf disks in solutions of NaHCO3 and H2O under soft white incandescent 60 W and full
spectrum/ daylight incandescent 60 W light bulbs were made, one could hypothesize that light
bulb color tone does not affect the production of O2 during photosynthesis.
Materials and Methods:
To begin, 300 mL of NaHCO3 solution and 300 mL of prepared DI water solution were
obtained in beakers (both solutions already contained dilute liquid soap). Since the two solutions
looked similar, each was labeled with its content. Four plastic cups were then obtained and
labeled with colored tape to identify which treatment and solution was to go in which. Cup A
contained NaHCO3 solution and had a specific light source. Cup B contained H2O solution and
had the same specific light source. Cup C contained NaHCO3 solution and had a different light
source. Cup D contained H2O solution and had a different light source. On each cup, a threecentimeter line was marked form the bottom and the appropriate solutions were poured into each
cup. Two stirring sticks were also labeled specifically to the two different solutions.
Cut ten (10) uniform leaf disks for each treatment or control
Next, a fresh leaf was placed on a smooth section of Styrofoam. A cork borer was then
used to push down on a leaf with even pressure to punch out each circle. Ten uniform leaf disks
were used for each treatment or control. Major veins, damaged areas, and leaf edges were
avoided and a wooden stick was used to gently remove disks from the borer.
Degas and infiltrate the leaf disks with the appropriate solution
To degas and infiltrate the leaf disks with the appropriate solution, the plunger was
removed and the leaf discs were placed into the syringe barrel. The plunger was then replaced
while being careful not to crush the leaf discs, and it was pushed until only a small volume of air
remained in the barrel. Four milliliters of the appropriate solution (NaHCO3 solution or H2O
solution) was pulled into the syringe. The syringe was then tapped to suspend the leaf discs in
the solution. A finger was then placed over the syringe tip opening and the plunger was drawn
back to the ten milliliter mark which created a vacuum; this position was held for up to 30
seconds or until the leaf discs floated. While the position was held, the solution and discs were
swirled to suspend the disks in the solution. Air coming out of the discs should be noted at this
time due to oxygen being removed form the spongy layer of the leaf (mesophyll). The vacuum
was then released by uncovering the syringe tip. The plunger was pushed until all of the air left
the syringe. The solution was then swirled and tapped so that disks dislodged from the sides and
settled. If the disks did not sink, the previous degasing steps were repeated. Once the discs no
longer floated, the investigations began. Leaf disks that did not remain at the bottom were
removed and replaced before beginning the investigation.
Perform the Experiment
Once the cups were in position for the appropriate experiment, one-minute intervals were
timed and recorded. After each minute, the contents in the cups were gently swirled with the
appropriately labeled sticks to dislodge the disks that were stuck to each other of the side of the
cup. The disks were allowed to settle before the number of floating discs was recorded in the
data table. The cups were immediately returned to their respective treatments. This recording
was continued for twenty intervals.
Light Bulb Type
After the above steps of preparing, cutting ten uniform disks, and degasing were taken,
Cup A containing NaHCO3 solution and ten uniform and degased disks was placed 21
centimeters underneath a light source with a soft white compact fluorescent 15 watt light bulb.
Cup B containing H2O solution and ten uniform and degased disks was placed 21 centimeters
underneath the same light source of soft white compact fluorescent 15 watt bulb. Cup C
containing NaHCO3 solution and ten uniform and degased disks was placed 21 centimeters
underneath a 60 watt soft white incandescent light bulb. Cup D containing H2O solution and ten
uniform and degased disks was placed 21 centimeters underneath the same light source of 15
watt soft white incandescent light bulb. The above “perform the experiment” steps were then
taken and data was recoded and observed.
Light Bulb Color Tone
After the above steps of preparing, cutting ten uniform disks, and degasing were taken,
Cup A containing NaHCO3 solution and ten uniform and degased disks was placed 21
centimeters underneath a full spectrum/daylight incandescent 60 watt light bulb. Cup B
containing H2O solution and ten uniform and degased disks was placed 21 centimeters
underneath the same light source of full spectrum/daylight incandescent 60 watt light bulb. Cup
C containing NaHCO3 solution and ten uniform and degased disks was placed 21 centimeters
underneath a 60 Watt soft white incandescent light bulb. Cup D containing H2O solution and ten
uniform and degased disks was placed 21 centimeters underneath the same light source of 15
watt soft white incandescent light bulb. The above “perform the experiment” steps were then
taken and data was recoded and observed.
Results:
In Figure 2 shown below, one can see that the 60 watt full spectrum/daylight incandescent light
bulb had a T50 of 5.6 minutes. The 60 watt soft white incandescent light bulb had a T50 of 5
minutes and a rate of 1 disk per minute in the NaHCO3 solution. In Figure 1 shown below, one
can see that the T50 for the 15 watt soft white compact fluorescent light bulb is at 5.5 minutes and
Number of floating leaf disks
has a rate of 1.1 disks per minute.
10
9
8
7
6
5
4
3
2
1
0
60 W full
spectrum/
daylight
incandecse
nt
60 W soft
white
incandesce
nt
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (min)
Number of floating leaf disks
Figure 2. Number of floating disks in NaHCO3 under a 60 W full spectrum/ daylight
Incandescent light bulb and under a 60 W soft white incandescent light bulb.
10
9
8
7
6
5
4
3
2
1
0
15 Watt soft
white
incandescent
60 Watt soft
white
incandescent
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Time (min)
Figure 1. Number of floating disks in NaHCO3 under 60 W soft white incandescent light bulb
and under a 15 W soft white light bulb.
Table 2. Number of floating leaf discs in NaHCO2 and H2O at one minute intervals under full
spectrum/ daylight incandescent 60 W light conditions and under soft white incandescent 60 W
light conditions.
Time
(minutes)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Experimental
group: A
(Full spectrum/
daylight
incandescent
60 W and
NaHCO3)
2
4
4
4
4
4
6
8
9
9
9
9
9
9
9
9
9
9
9
9
Control group:
B
(Full
spectrum/
daylight
incandescent
60 W and
H2O)
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
Experimental
group: C
(Soft white
incandescent
60 W and
NaHCO3)
Control group:
D
(Soft white
incandescent
60 W and
H2O)
0
0
3
4
5
6
6
7
7
7
7
7
7
7
7
8
8
9
9
9
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
Table 1. Number of floating leaf disks in NaHCO3 and H2O at one minute intervals under 15
watt light condition and 60 W light condition.
Times
(minutes)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Experimental
group: A
(15W and
NaHCO3)
0
0
0
0
4
6
6
6
7
7
7
7
7
7
7
7
7
7
7
7
Control
group: B
(15W and
H2O)
0
0
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
Experimental
group: C
(60 W and
NaHCO3)
0
0
3
4
5
6
6
7
7
7
7
7
7
7
7
8
8
9
9
9
Control
group: D
(60 W and
H2O)
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
From Figure 2, one can see that the 15 W soft white compact fluorescent light bulb and the 60 W
soft white incandescent light bulb both different T50; the 60 W is higher. The 60 W also had 9
disks floating in the NaHCO3 solution after 20 minutes compared to 7 under the 15 W light
source. The 60 W full spectrum/daylight incandescent light bulb has a higher T50 than then 60 W
soft white incandescent light bulb. According to Table 2 above in the experiment for light bulb
type, after 17 minutes the 60W soft white incandescent light bulb had more floating disks than
did the 15 W soft white compact fluorescent light bulb. There were a limited number of disks
floating at the end of the measured time in Group B and D in Table 1 and 2, and these were the
control groups in the experiments.
Discussion:
In the experiment comparing light bulb type, the 60 W light bulb had a higher T50 than
the 15 W light bulb did. The 60 W had a T50 of 1 disk per minute while the 15 W had a T50 of
.91 disk per minute. The 60 W light bulb produced a higher rate of photosynthesis than the 15 W
light bulb because there was more floating discs at the end of 20 minutes under the 60 W light
bulb. The results differed than what was expected when there was a statistical difference in the
number of floating leaf disks in the NaHCO3 solution between the 15 W light bulb and the 60 W.
In an experiment done by Pastenes and Horton (1996), it was found that high temperature from
light changed the thylakoid membrane in plants and resulted in an increase in the rate of
photosynthesis. The significance of these results is that one can see that NaHCO causes
photosynthesis to proceed at a faster rate under a higher wattage light bulb. From this, one can
deduct that 60 W makes photosynthesis proceed at a faster rate than the 15 W light bulb. The
results from the experiment reject the hypothesis that light bulb type does not have an affect on
the production of oxygen in photosynthesis.
Light bulb color tone was found to affect the production of oxygen during photosynthesis
because the 60 W soft white incandescent had a T50 of 1 disk per minute, and the 60 W full
spectrum/daylight incandescent light bulb had a T50 of .78 disk per minute even though they both
had nine leaf disks floating after 20 minutes of recording. The soft white incandescent light bulb
had a higher T50 than the full spectrum/daylight light bulb did, but they both ended the
experiment with the same number of leaf disks floating. Results from the experiment support the
hypothesis that light bulb color tone does not have an affect on the production of oxygen in
photosynthesis. The significance of these results is that light bulb tone has an affect on the rate
of photosynthesis. From this, one can deduct that plants will grow faster under the soft while
light bulb compared to the full spectrum light bulb.
If this experiment were to be replicated, one could do multiple tests under each
experiment to make sure that the results matched. One could do this by preparing two cups of
the solution and leaf discs to place under the given condition and compare results. NaCHO3
reaction to light could also be more closely studied. One could ask if the distance of the solution
from the light source makes a difference in the number of floating leaf discs in the experiment
with light bulb color tone and the experiment with light bulb type. For further testing the rate of
photosynthesis one could use different wattage light bulbs to see their effects. One could also
use different solutions like salt water or pop under the 15 W and 60 W light bulbs to see if the
number of floating leaf discs changes. Potential sources of error include differences in how long
the solutions were stirred for to mix the content in each experiment. One experiment was stirred
for three seconds while the other did not record time. The experiment was also done in a group
rather than by a single person so there was different people conducting the many steps, so there
was not a control.
Literature Cited
Johnson, Raven, Mason, K. Losos, J., & Singer, S. (2014). Photosynthesis. In BIOLOGY. New
York: McGraw-Hill.
Mouget, J. L., Rosa, P., Vachoux, C., and Tremblin, G. (2005). Enhancement of marennine
production by blue light in the diatom Haslea ostearia. Journal of Applied Phycology.
Pastenes, C., & Horton, P. (1996). The effect of high temperature on photosynthesis in beans:
I. Oxygen evolution and chlorophyll fluorescence. Plant Physiology.
Vodopich, D. S., and Moore, R. (2014). Biology laboratory manual. McGraw-Hill.