The document describes a lab experiment that tested how the rate of photosynthesis is affected by leaf color. Students used leaf disks of light green, dark green, and yellow leaves submerged in a sodium bicarbonate solution. They measured the time it took for each disk to rise to the surface as photosynthesis replaced air space with oxygen. Results showed yellow leaf disks rose fastest, suggesting color affects light absorption and therefore photosynthesis rate.

1. SukYoung Cho
IB Biology SL
Period 2
Floating Leaf Disk Photosynthesis Lab
Introduction
Photosynthesis is the process in which plants and bacteria use the energy from sunlight to
produce sugar; where cellular respiration converts into ATP. This process may seem
unimportant, but is a complicated process which serves as a ‘fuel’ to some organisms. Within
a plant, photosynthesis occurs in the chloroplast, an organelle that contains chlorophyll. This
organelle absorbs the energy provided by sunlight and that energy is then converted into a
chemical energy through photosynthesis. Photosynthesis is sometimes defined as the
‘physico-chemical processes.’
The rate at which photosynthesis functions can be varied depending on the factors; for
instance, light intensity, temperature, and the level of water. Furthermore, the rate could
change with the change in color, shape, size, and even the position of a leaf. This lab focuses
on how the color change in the leaf changes the rate of photosynthesis. First it was
hypothesized that color will affect the photosynthesis rate of a leaf because every color
absorbs and reflects different wavelengths; therefore, the light intensity absorbed will differ
as well. To find out whether this idea was true the lab tests:
Does the Difference in Color of a Leaf Change the Rate of Photosynthesis?
Leaves when placed in water naturally float. However, when the air space in the leaf is
replaced by another solution, the density of the leaf increases and causes the leaf to sink. In
the lab, the solution which replaces the air space is made of 50mL of water and 1g of sodium
bicarbonate. The lab uses this solution instead of water because; it helps speed the process by
providing more carbon dioxide. After the leaf disk has sunk, photosynthesis again replaces
the solution with oxygen which creates a space inside the leaf. The oxygen replacement
changes the buoyancy of the leaf and causes them to rise to the surface.
6CO2 + 6H2O + Energy C6H12O6 + 6O2
The equation produced above is six molecules of water + six molecules of carbon dioxide
produce one molecule of sugar + six molecules of oxygen. This formula is the equation for
the process of photosynthesis.
Figure 1: This diagram shows
the process at which the
solution containing water and
sodium bicarbonate replaces the
air space within a leaf disk.

2. Research Question
Does the Difference in Color of a Leaf Change the Rate of Photosynthesis?
Variables
The independent variable was the colors of the leaf: the colors included light green, dark
green, and yellow. The dependent variable then was the time each leaf disk took to rise back
to the surface of water: The dependent variable was measured by a stop watch to keep the
time measurement exact. There were several constants which were involved. The first
constant was the type of beaker used for the three types of leaf disks. The second constant
was the size of each leaf disks: this was kept controlled by using a hole-puncher, cutting out
the leaf with an exact circled disk. The third constant was the amount of water (50mL) and
the amount of sodium bicarbonate (1g) to make the solutions that would replace the air space
inside each of the leaf disks. The fourth constant was the angle and distance at which the
beakers containing the leaf disks were from the light source, lamp. Another variable that was
kept the same was the heat at which each leaf disk was exposed to. The rate of photosynthesis
can differ if heat is added as a factor; so to keep heat to a minimum, a water filled aquarium
was placed between the light source and the beakers. The water then helped absorb all the
heat produced by the lamp, but did not affect the transference of light to the beakers.
Materials
 3 small beakers
 450mL of water
 9g of sodium bicarbonate
 Hole puncher
 Lamp
 Stop Watch
 3 Syringes
 Small aquarium
Figure 3: This diagram demonstrates the
Figure 2: This picture shows the preparation stages at which the air is taken out of the
of punching out disks on the leaf and putting leaf disks to replace with the made
them into the syringe. solution.

3. Procedure
Before the experiment is conducted, make sure that all the materials above are prepared and
set-up. Set up each of the 3 beakers with exactly 1g of sodium bicarbonate and; set up so that
there is a place for the beaker, lamp, and the aquarium between the two. Then add enough
water into the aquarium so that it is well over half the total volume. And make sure that there
is no strong light surrounding the experimental area because light automatically starts the
photosynthesis process.
After the steps above are completed prepare three different leaves each with different colors.
For this experiment leaves with the color yellow, dark green, and light green were gathered.
Make sure that there is more than plenty because 3 trials will require a lot of samples. With a
hole-puncher, shape out fifteen punches for each leaf sample, so total there will be 45 leaf
disks to experiment with. Add fifteen of the same colored leaf disks into the prepared syringe
and then add 50mL of water into them; be aware that water will exit through the bottom of
the syringe. First, close the syringe and have all the air inside escape by pushing the syringe
inward till all air is out. Then with all the lights off in a room, close the exit of the syringe
with fingers or a stopper and pull the syringe outwards so that it creates a vacuum. Letting go,
leave the syringe in a dark area so that photosynthesis does not start early, but all the leaf
disks get to reach the bottom. Repeat the steps above for 2 of the other colored leaves.
Prepare to record data with a stop watch to time when each leaf starts floating.
Place three of the beakers in front of the aquarium and have the lamp turned on so that it is
able to shine upon all three beakers with the same intensity. Then take out the three syringes
and squeeze out 2/3 of the water into each of the separate beakers. After mixing the solution,
add the remaining 1/3 of water and leaf disks by opening the top and pouring it in the beaker.
Repeat the steps for 2 of the other syringes. With the lamp turned on, start collecting data.
Every time that a leaf disk touches the surface of the water, note the time taken.
(be aware that sometimes a couple of leaf disks rise together)
Figure 4: This figure shows a person creating a Figure 5: This picture shows the data collection
vacuum within the syringe, so that the air space scene, where the leave disks are rising due to
inside the leaf disk is removed. photosynthesis; and time is being measured with a
stop watch.

4. Data Collection and Processing
The tables below represent each of the times collected for when a leaf disk rose and reached
the surface of the beaker solution. Each table includes three different leaf colors: light green,
dark green, and orange.
1st Trial (First 15 set)
Time (±0.008minutes)
Leaf Disk Number
Light Green Color Dark Green Color Yellow Color
(minutes/sec) (minutes/sec) (minutes/sec)
1 0:02 0:02 0:02
2 0:02 0:02 0:02
3 0.02 0:02 0:02
4 0:02 6:00 0:02
5 4:00 7:00 0:02
6 4:20 7:02 0:02
7 4:47 11:05 0:02
8 5:17 11:06 0:02
9 6:36 13:25 0:02
10 6:44 16:40 0:02
11 7:54 18:28 0:02
12 8:55 19:33 2:00
13 10:22 27:54 none:
14 13:28 30:21 none:
15 14:58 39:48 None
Avg. Time 6:15 14:27 0:02
Table 1: This table shows the times recorded for each color of the rises of leaf
disks. (the first set of 15)

5. 2nd Trial (second 15 set)
Time (±0.008minutes)
Leaf Disk Number Light Green Color Dark Green Color Yellow Color
(minutes/sec) (minutes/sec) (minutes/sec)
1 0:00 0:00 0:02
2 5:36 0:00 0:02
3 6:00 2:11 0:02
4 6:00 5:34 0:02
5 6:00 6:10 0:02
6 6:12 7:11 0:02
7 6:47 9:22 0:02
8 6:47 10:38 0:02
9 7:00 12:35 0:02
10 7:01 14:30 0:02
11 7:02 17:29 0:02
12 7:04 17:29 2:00
13 7:39 20:31 none:
14 7:40 27:21 none:
15 7:50 35:09 none
Avg. Time 6:18 12:27 0:02
Table 2: This table shows the times recorded for each color of the rises of leaf
disks. (the second set of 15)

6. 3rd Trial (final 15 set)
Time (±0.008minutes)
Leaf Disk Number Light Green Color Dark Green Color Yellow Color
(minutes/sec) (minutes/sec) (minutes/sec)
1 0:01 0:01 no result
2 1:00 0:01 no result
3 3:13 2:30 no result
4 4:12 2:30 no result
5 4:13 2:57 no result
6 4:13 5:20 no result
7 4:14 5:58 no result
8 4:39 5:59 no result
9 5:25 6:00 no result
10 5:28 6:01 no result
11 5:29 8:01 no result
12 7:14 8:04 no result
13 7:24 9:39 no result
14 8:00 9:45 no result
15 8:03 9:50 no result
Table 3: This table shows the times recorded for each color of the rises of leaf disks.
(the third set of 15)

7. Figure 6: This is a graph which shows the
correlation between the colors of the leaf
disks and the point of time at which they
finish photosynthesis.
KEY: Yellow – Yellow Disk
Dark Green – Dark Green Disk
Light Green – Light Green Disk
Figure 7: This is a graph which shows the
correlation between the colors of the leaf
disks and the point of time at which they
finish photosynthesis.
KEY: Yellow – Yellow Disk
Dark Green – Dark Green Disk
Light Green – Light Green Disk
Figure 8: This is a graph which shows the
correlation between the colors of the leaf
disks and the point of time at which they
finish photosynthesis.
KEY: Yellow – Yellow Disk
Dark Green – Dark Green Disk
Light Green – Light Green Disk

8. Unpaired T Test Results
- Light Green Leaf and Dark Green Leaf
P value and statistical significance:
The two-tailed P value equals 0.0236
By conventional criteria, this difference is considered to be statistically significant.
Confidence interval:
The mean of Light Green Leaf minus Dark Green Leaf equals -471.93
95% confidence interval of this difference: From -875.68 to -68.18
Intermediate values used in calculations:
t = 2.3943
df = 28
standard error of difference = 197.105
Review your data:
Group Light Green Leaf Dark Green Leaf
Mean 361.93 833.87
SD 286.13 707.73
SEM 73.88 182.74
N 15 15
Sample Calculations
Average Time Rise for Green Color Leaf
 3rd trial data – dark green color

Rate of Photosynthesis (seconds)
 3rd trial data – dark green color

9. Conclusion
This lab was set, to determine whether the color of the leaves affects the rate at which
photosynthesis functions. It was hypothesized that the darker green leave’s photosynthesis
rate will noticeably be faster than those of the lighter green leaves and the yellow colored
leaves. To find the rate of photosynthesis, the O2 production rate was measured. As
hypothesized, results shows that the darker the color, the faster the photosynthesis rate. After
this experiment, online research helped proved why this was the case. Darker leaves have a
significantly higher rate of photosynthesis than lighter leaves, because the dark green leaf
contained more green chlorophyll a and chlorophyll b pigments than the lighter colored
leaves had.
Furthermore, to see if the data collected was reliable, a t-test was conducted. As shown in the
‘data collection’ section above, the rate of photosynthesis for the dark green leaf and the light
green leaf compared with a P value of 0.0236. This t-test shows that ‘this difference is
considered to be statistically significant’.
Therefore, the data collected and the validity of the experiment shown in the t-test helps show
that color of a leaf does determine and change the rate at which photosynthesis occurs.
Evaluation
One of the major sources of random error was the decision for the independent variable: color
of the leaf. To compare the relationship and comparison of the rate of photosynthesis, a valid
difference was to be chosen. However, there are several disadvantages in differing leaves by
the color. This is because; choosing leaves with different colors often mean that the types of
leaves chosen are different species. Therefore, a type of leaf may commonly be thinner than
the other type; and thickness of a leaf is a major factor in changing the rate of photosynthesis.
If the true research was based on the idea that different colors affect the rate of
photosynthesis, all of the leaves chosen for the experiment should have been from the same
species.
The second major source of random error could have been involved in the process of creating
a vacuum within the syringe. In this procedure, the air space within the leaf disk is removed
by creating a vacuum within a syringe. However, some leaf disks could have had more air
space removed than others. If this was the case, the time/rate at which each leaf disk rose to
the solution surface could be inaccurate. The best approach to solving this error can be
creating the vacuum multiple times; by using a stopper to close the exit and pulling the
plunger several times.
A final major source of random error was the difference of color/shade from the top side of a
leaf disk and the bottom side of the disk. The difference of the shade on the leaf disk most
likely affected the rate of photosynthesis. This observation helps support the data of some leaf
disks which, compared to other leaf disks, rose rather slowly or quickly. To improve the
method, it would be important to use a stirring tool to flip some of the disks during the
experiment.