1. Kai Hondo
Biology SL
How light wavelength affects photosynthesis?
Introduction:
Photosynthesis is a reaction when plants use light and carbon dioxide to produce energy
and oxygen. The equation of the photosynthesis is that:
������������������������������
6H2O + 6CO2 6O2 + C6H12O6
Plants need pigment to catch and absorb light energy to start reaction of photosynthesis and the
pigment which plants mainly used is Chlorophyll a. The graph below, it shows absorbance of
Chlorophyll a and Chlorophyll b in different wavelength and as the graph, Chlorophyll a mainly
absorbs blue light (around 435nm wavelength) and red light (around 680nm wavelength) and
Chlorophyll a does not absorb green light. Sometimes, plants also use the other pigments such
as Chlorophyll b, Carotene, and xanthophylls to support absorbing light energy.
In this experiment, we are going to define
the connection between rate of photosynthesis and
light wavelength to limit color (wavelength) of light
which plant (leaf) can absorb for photosynthesis. In
the experiment, leaves are sunk into five (red, green
blue, and violet) different food coloring NaHCO3
solutions. These five different food colorings are
used to limit color of light. If experiment goes
successfully, leaves in the green solution flow first
and leaves in the red solution flow last because of
this, plant does not use green color for
photosynthesis but plant use red color so, using
green food coloring to limit green light does not
affect the leaves photosynthesis than the red color.
NaHCO3 is used to increase the rate of
photosynthesis because in the nature,
photosynthesis takes more than one hour.
Design:
Independent variable: limited color (wavelength)
Dependent variable: amount of pigment each leaves have
Control variable: light intensity, temperature of water, amount of light: These control variables
affect the result of the experiment but light intensity and amount of light are measured by the
light probe carefully and temperature of water is also measured by thermometer so, affect of
these factors will be minimum.

2. Procedure:
1) Mix 1000mL of 4% NaHCO3 solution (50mLs per bottle × 4 trials) *
2) For each of the 4 colors:
Water & food coloring in 200mL beaker to get approximately 700lux light intensity
based on the light probe reading. (Make sure the beaker & light probe is placed in the
marked position)
3) Punch out 100 pieces from dark green leaves using a hole-puncher (15 per bottle × 4 trials)*:
Put these in a small beaker/ bowl and place in the dark (i.e. cupboard)
4) Fill aquarium with 29 degree water (mark bottle position & attach thermometer to a side)
5) Place 2 lamps (equal light intensity  forgot the value/ what type) equidistant from
aquarium
6) TO be repeated for 4 trials steps
a) Fill 4 small bottles each 50mL with one of the colored water & 50mL solution
b) Place rubber bands around 4/5 way of the bottles
c) Drop 15 leaves into each bottle
d) Place the bottles in designated areas within aquarium
e) Start timer & record
7) Repeat step 6 for 3 more trials
*leftover is for backup
Picture 1: four different food coloring Picture 2: Use aquarium to keep temperature
Data Collection
Trial 1:
leaf # red green blue violet
1 3:32 4:37 3:27 3:19
2 3:34 4:48 3:45 3:37
3 4:59 5:08 5:31 3:45
4 5:05 5:21 5:32 4:31
5 5:06 5:35 5:36 4:32
5 5:19 6:00 5:46 4:34
6 5:40 6:07 5:52 5:01
7 5:42 6:58 5:58 5:34

3. 8 6:29 7:07 6:02 5:43
9 6:55 7:13 6:31 6:01
10 6:57 7:32 6:49 6:14
Trial 2:
leaf # red green blue violet
1 3:41 4:01 3:35 3:18
2 4:28 4:09 3:55 3:18
3 4:57 4:15 3:56 3:28
4 5:09 4:17 3:57 3:30
5 5:13 5:58 4:44 4:27
5 5:14 7:04 4:59 4:57
6 5:30 7:17 5:10 5:19
7 5:31 7:20 5:34 5:23
8 5:59 7:24 5:45 5:47
9 6:04 7:34 6:11 5:48
10 6:15 9:18 6:12 5:56
Trial 3:
leaf # red green blue violet
1 3:21 3:56 3:19 3:12
2 3:35 4:15 3:31 3:14
3 3:44 4:23 3:36 3:26
4 3:44 4:58 3:48 3:27
5 4:20 5:01 4:56 4:13
5 5:27 5:02 5:02 4:38
6 5:39 6:25 5:29 5:07
7 5:56 6:53 5:51 5:50
8 6:15 7:00 5:56 6:02
9 6:25 7:17 6:35 6:18
10 6:43 7:24 6:40 6:22
Trial 4:
leaf # red green blue violet
1 3:29 3:38 3:30 3:08
2 3:00 4:03 3:56 3:11
3 3:00 4:03 4:13 3:26
4 4:00 5:14 4:15 3:34
5 4:36 5:35 4:16 4:03
5 4:42 5:36 4:17 4:32

4. 6 5:16 5:41 4:47 4:48
7 5:31 6:23 5:24 4:55
8 5:52 6:52 5:25 5:30
9 6:05 7:18 5:58 5:42
10 6:24 8:06 6:21 5:49
Data Analysis:
Average time leaves take to flow in each color
blue red green violet
5:05 5:54 5:02 4:38
Figure 1: Average time leaves take to flow in each color
Average Time
7:12
6:00
4:48 blue
red
3:36
green
2:24 violet
1:12
0:00
Conclusion:
As the data of figure 1, we can know that red color is most important color for plants to
do photosynthesis because leaves which limited red color rise slowest. However, the other
results are not supported the theory of photosynthesis. By the theory, leaves which limited
green color should rise fastest because plants does not use green color so much to do
photosynthesis. However, the result shows that leaves which limited violet color rise fastest.
Evaluation:
I think the food coloring we used is too pale so, maybe it does not limit wavelength of
light completely.