The document summarizes an experiment that tested how the rate of photosynthesis is affected by the color of leaves. 15 disks were punched from two different colored leaves (light green and dark green) and their floating times in a sodium bicarbonate solution were recorded over 4 trials. The average rate of photosynthesis was then calculated for each leaf type based on the time it took for the disks to float. The results showed that the light green leaf disks floated faster, indicating a higher rate of photosynthesis, compared to the dark green leaf disks.

1. Honori Yamada
Biology SL 2
Mar/12/11
The Effect of the Rate of Photosynthesis on Different Leaves
Introduction:
Oppositely from cellular respiration, photosynthesis is a chemical reaction in
which autotrophs or green plants produce their own food and as a byproduct, they
synthesize glucose and oxygen. In order for photosynthesis to process, three
fundamental inorganic compounds are needed along with the plant: carbon dioxide
(CO2), water (H2O), and light intensity. This overall reaction of the photosynthesis
process can be written as a equation:
6H2O + 6CO2  C6H12O6+ 6O2(1)
where6H2O indicates six water molecules, 6CO2are six carbon dioxides, C6H12O6 is
glucose, and 6O2 refers to six oxygen molecules. The process of photosynthesis shows
how photosynthetic organisms store light energy, water, and carbon dioxide to create
glucose and oxygen. Oxygen is released in the atmosphere whereas glucose is used at a
later time to supply the energy needs of the cell.
Combining of these elements to produce sugar and oxygen takes place in the
chloroplast which includes chlorophylls that associate with the action of the green
pigment. A pigment is any substance that absorbs light. The wavelength of the light
reflected or absorbed determines each color of the pigment. Chlorophyll, which is a
green color pigment, tends to absorb all wavelengths of visible light except green. Since
chlorophylls do not absorb the light with the specific wavelength of color green, it
reflects back to be detected by our eyes. This is the reason why leaves are green; the
color green could not be absorbed by the chlorophylls in the cells that the light reflects
back to our eyes making it visible for humans to see.
In this research, the experiment will be investigated on whether the color of the
leaves will affect the rate of photosynthesis. Throughout this experiment, 15 hole
punched disks of leaves will be placed in a water filled syringe to such out the oxygen in
the leaf disks by drawing back the plunger to create vacuum. Then, the leaf disks will be
inserted into a 2% sodium bicarbonate (NaHCO3) solution. Photosynthesis will further
occur when the leaf disk inserted solution is placed where the light from the lamp is
directly shined through, making it a light-dependent reaction. The leaf disks are
gradually going to create oxygen that will change the buoyancy – causing the disks to
float.
At first, the leaf disks in the water filled syringe all float because the disks insist
small oxygen particles. However, since this experiment tests the rate of photosynthesis
in the leaves, the leaf disks are drawn back with a plunger in order to suck out the

2. Honori Yamada
Biology SL 2
Mar/12/11
oxygen until each pieces sink. During this experiment, sodium bicarbonate, that has
carbonate ions will be used as it serves as the carbon source for photosynthesis. As
sodium bicarbonate dissolves in water, carbonate ions appear as it absorbs into the leaf
disks – making it a carbon dioxide gas. Therefore, sodium bicarbonate will be used
throughout this lab in order to quicken the rate of photosynthesis.
Design:
Research Question:
How will the difference in the color of the leaves affect the rate of photosynthesis?
Table 1: Important Variables
Variable Type How
Types of Leaves Independent Variable Picked up 2 different leaves
with different colors (light,
dark)
Length of time (rate of Dependent Variable Stopwatch
photosynthesis)
Circumference of leaf disks Controlled Variable Hole puncher
Concentration of solution Controlled Variable Electronic Balance, beaker,
- Amount of sodium water, stirrer, sodium
bicarbonate bicarbonate
- Amount of water
Temperature Controlled Variable Water tank, thermometer
Size of Beaker Controlled Variable -------------
Light intensity Controlled Variable Ruler, pencil, beaker, lamp
Table 1▲: These are the important independent, dependent, and controlled variables
that are shown as well as the process of how it was done.
Materials:
- Leaves (2 types)
- Hole puncher
- Syringe
- Beaker
- Water
- Sodium bicarbonate
- Thermometer Figure 1: Sodium Bicarbonate,
- Electronic Balance syringe, beaker, stopwatch,
- Stopwatch leaf A and B are shown. Figure 2:The water tank and
- Water Tank
- Lamp the lamp are shown which
controlled the temperature

3. Honori Yamada
Biology SL 2
Mar/12/11
Procedure:
1. Prepare a beaker and add 1g of sodium bicarbonate on an electronic balance
2. Get a water tank and fill the water about half way through
3. Prepare the experiment by placing the water filled tank in front of the lamp then
the beaker in front of the tank so that the light shines through the water tank,
then to the beaker in order to keep the temperature controlled(Figure 3)
4. Trace a mark of the beaker onto the table so that the light intensity would also be
controlled
5. Go outside and find two different types of leaves with a different color (one light
green, one dark green)
6. Hole punch 15 pieces of disks from one type of leaf
7. Place the 15 disks into the syringe
8. Prepare 50ml of water and draw in the water with the syringe (the disks should
all float)
9. Hold a finger over the syringe opening and draw back on the plunger to create
vacuum for 30 seconds
10. Repeat the vacuum until all the leaf disks sink to the bottom
11. Hold a finger over the syringe opening and remove the plunger
12. Pour in most of the water in the syringe into the beaker with the sodium
bicarbonate and stir it will
13. After the solution is mixed, pour in the rest of the water with the disks
14. Insert a thermometer to keep the temperature controlled and consistent
15. Once the lamp is switched on, start the stopwatch and record the data
Figure 3▲: The figure above shows the setting of the experiment so that the light does
not affect the rate of photosynthesis by using a water tank.

4. Honori Yamada
Biology SL 2
Mar/12/11
Data Collection and Processing:
Table 2:Time Length for Leaf A Disks to Float
# of floated Trial 1 (sec) Trial 2 (sec) Trial 3 (sec) Trial 4 (sec)
disks
1 34 107 73 6
2 55 187 92 25
3 62 226 116 63
4 216 246 147 107
5 235 266 168 123
6 254 267 218 136
7 277 276 229 147
8 289 284 242 162
9 323 298 252 173
10 345 322 260 216
Table 2▲: The table above shows four trials of the time it took for all ten disks for Leaf A
to float.
Table 3:The Rate of Photosynthesis for each Trials and its Average Average Rate of
Groups: Trial 1 Trial 2 Trial 3 Trial 4 Photosynthesis
(sec) (sec) (sec) (sec)
10th Disk time 345 322 260 216 0.0036 ± 0.0009
Rate of 0.0029 0.0031 0.0038 0.0046
Photosynthesis
Table 3▲:The table above shows the calculated rate of photosynthesis of the four trials
and the average rate of photosynthesis for Leaf type A.
Table 4: Time Length for Leaf B Disks to Float
# of floated Trial 1 (sec) Trial 2 (sec) Trial 3 (sec) Trial 4 (sec)
disks
1 756 536 785 632
2 787 569 970 651
3 874 605 1105 789
4 1142 622 1138 997
5 1285 992 1162 1163
6 1349 1032 1202 1182
7 1369 1041 1246 1196
8 1396 1052 1337 1213
9 1405 1206 1415 1235
10 1453 1238 1457 1386
Table 4▲: The table shows four trials of the time it took for all ten disks for Leaf B to
float.

5. Honori Yamada
Biology SL 2
Mar/12/11
Table 5: The Rate of Photosynthesis for each Trial and its Average Average Rate of
Groups: Trial 1 Trial 2 Trial 3 Trial 4 Photosynthesis
(sec) (sec) (sec) (sec)
10th Disk time 1453 1238 1457 1386 0.00073 ± 0.00012
Rate of 0.00069 0.00081 0.00069 0.00072
Photosynthesis
Table 5▲:The table above shows the calculated rate of photosynthesis of the four trials
and the average rate of photosynthesis for Leaf type B.
Sample Calculations:
i. Changing the Time from Minutes to Seconds (Leaf B Trial 1 Disk 10)
= minutes × 60 + seconds
= 24 × 60 + 13
1453 seconds
ii. Calculating the Rate of Photosynthesis (Leaf A Trial 1)
= 1/time length it took for the 10th disk to float
= 1/345
0.0029 (s-1)
iii. Calculating the Average Rate of Photosynthesis (Leaf A)
= (Add the rate of photosynthesis for all four trials)/4
= (0.0029 + 0.0031 + 0.0038 + 0.0046) / 4
0.0036 (sec)
iv. Calculating the Uncertainties (Leaf A)
= range of the rate photosynthesis /2
= (0.0046 – 0.0029) / 2
= 0.0017 / 2
±0.0009

6. Honori Yamada
Biology SL 2
Mar/12/11
Figure 4▲:The graph above shows the difference of the average rate of photosynthesis
with leaf type A and B.
T-Test Results:
Using the statistical program from the site of http://graphpad.com/quickcalcs, the
unpaired T-test was performed for all the 80 raw data of Leaf A and B.
P value and statistical significance:
The two-tailed P value is less than 0.0001
By conventional criteria, this difference is considered to be extremely statistically
significant.
Confidence interval:
The mean of Leaf A minus Leaf B equals -886.15
95% confidence interval of this difference: From -977.33 to -794.97
Intermediate values used in calculations:
t = 19.3491
df = 78
standard error of difference = 45.798

7. Honori Yamada
Biology SL 2
Mar/12/11
Review your data:
Table 6: The Statistical Difference of Leaf A and B
Group Leaf A Leaf B
Mean 188.10 1074.25
SD 92.40 274.52
SEM 14.61 43.41
N 40 40
Table 6▲: The table above shows the results of the differences in the two types of leaves
by the T-test.
Conclusion & Evaluation:
Conclusion:
According to graph in figure 4, there is a great different in the average rate of
photosynthesis for leaf A and B. With leaf A, the rate of photosynthesis was 0.0036s-1
whereas with leaf B, the rate was 0.00073 s-1having the difference of around 0.00029s-1.
This relatively huge difference in the average rate between the two types of leaves signify
that the rate of photosynthesis can be effected by the type of leaves. As leaf B has a
smaller rate than leaf A, this shows how leaf B took a longer time for the process of
photosynthesis than leaf A. Although this experiment showed a relative difference in the
two types of leaves, the reason to the result cannot be proven. However, it can be
predicted that either leaf A had more chlorophyll than leaf B, or that leaf B was thicker
in size than leaf A. Again, for either reason, it can be concluded that the different type of
leaves do make a difference in the rate of photosynthesis.
Not only was the data compared by graphing the rate of photosynthesis, but also
the unpaired data T-testing was programmed in order to further verify that there is a
significant statistical difference in the two rates of photosynthesis. By adding all forty
raw data for each leaf, the calculation which compared the differences in the two rates of
photosynthesis showed a statistically significant difference. Below the “Confidence
Interval”, the mean difference of leaf A and B was886.15. This clearly shows an
extremely large difference in rate of photosynthesis. Not only, but even by taking
account into the statistical error of 5%, the result shows that there will still be a
significant mean difference of 977.33 - 794.97. Therefore, it could be stated both
statistically and mathematically that the type of leaves do affect the rate of
photosynthesis.
The uncertainties for type A and B were both relatively small. For leaf A, the
uncertainty was ± 0.0009whereas for leaf B, the uncertainty was ± 0.00012. This shows
how with leaf B, the results were not as consistent as with leaf A. One reason could be
because of the difference in the amount of chlorophyll in each leaf disks. As leaf A does

8. Honori Yamada
Biology SL 2
Mar/12/11
not have a big uncertainty amount as leaf B, it could be stated that the results of leaf A is
more reliable than leaf B.
Although the raw data consists the time lengths of up to fifteen leaf disks, this
experiment only measured the first ten leaf disks for a reason. The experiment tested
with fifteen disks in order to lessen the chance of errors. There is a probability that some
leaf disks were statistically an outlier. Shown in the raw data, some of disks did not float
up due to some errors that were caused during the process. If the calculations for the
rate of photosynthesis consisted up to fifteen disks for each trial, errors could have
resulted such as some outliers. Oppositely, using too little data could have resulted with
an inaccurate calculation of the rate of photosynthesis as some disks could have floated
too fast (oxygen was not completely expunged out of the disks or too many possible
chlorophylls in an area of the leaf disk). To compensate the effect of the outliers, the
concept of Exposure Time or ET50, created by Steucek, is a reliable index to this
research. The Exposure Time is the time it takes for half of the process (or 50%) to
change. By using the time it took for the tenth disk to float, it shows a relatively reliable
result of the rates of photosynthesis.
Evaluation:
Throughout this experiment, there was one big error which was choosing the
right type of leaves. On the first day, two different colored leaves were chosen without
being aware of the other differences such as the thickness and the size. This further
affected the results since the difference in the rates could have been due to the thickness
of the leaves or the different amount of the chlorophylls in a leaf. Therefore, since there
is more than one solution to why the rates differed with the different types of leaves,
nothing could be completely stated. This can be improved by choosing the same type of
leaf which consists of different colors (some parts light green, some parts dark green).
This can further make the experiment itself more precise and controlled as it only would
focus on whether the “color” of the leaf can affect the rate of photosynthesis.
Along with the type of the leaves, the accuracy in expunging all the oxygen out of
the disks by a syringe could have been an issue. Although the syringe was vacuumed
until all fifteen disks sunk to the bottom, it was not completely sure that all the oxygen
was out for all the disks, equally. As some of the data for the time length of disks 1-2
showed as relatively fast buoyancy change than the others, it could possibly be said that
the oxygen was not fully expunged for those. This can further be improved by drawing
back the plunger for as longer period of time, for example 30 seconds. Although this still
would not measure that all the oxygen would be out of the disks, there were still be a
higher chance of reliability.
To make a 2% solution with 50ml of water, 1g of sodium bicarbonate measured
and used. However, there was difficulty in measuring the exact amount of 1g sodium
bicarbonate. This could have affected the rate of photosynthesis since in some trials,
there could have been more carbon ions that would have fasten the rate than the other
trials. This could be improved for next time by doubling the amount of water so that the

9. Honori Yamada
Biology SL 2
Mar/12/11
amount of sodium bicarbonate would be doubled as well. By doubling the amount of
sodium bicarbonate, it would be easier to measure the exact amount that could be
controlled.
Weakness How/what Solve
Type of Leaves The thickness, size, and the Compare with the same leaf
color could have all affected that consist of different
the rate of photosynthesis colors (spotted leaves)
Expunging oxygen out In data, some disks showed Draw back the plunger for a
of Disks Completely a relatively fast buoyancy longer period of time
time than the others
Concentration of the Difficulty in measuring Double the amount of water
Solution exactly 1g of sodium so that the amount of
Bicarbonate sodium bicarbonate would
double as well, making it
easier to measure.
Amount of Chlorophylls Although used the same Make one or two more
in each Disks leaf, each disk could have trials so that the results
consisted a different could be more reliable.
amount of chlorophyll
which could have affected
the rate of photosynthesis
Table 7▲: The different weaknesses that appeared during the experiment and how it
should be solved is shown