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

𝐥𝐢𝐠𝐡𝐭 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.

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

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

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

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.

0:00

1:12

2:24

3:36

4:48

6:00

7:12

Average Time

blue

red

green

violet