Colors of Visible Light and Rate of Photosynthesis

By Madeline Carleton, Jackie Galli, and Maeve Merzena ♡

Which color(s) of visible light are plants

able to use the most efficiently in

photosynthesis?

Background InformationIt is important to understand that using a colored filter only allows certain colors of visible light through. White light contains all colors of visible light, all of which have different levels of energy based on the wavelengths. Refer to the diagram (right) to see which colors of visible light have the shortest and longest wavelengths, and therefore the most and least energy.

The Experiment

Hypothesis

Colors of light with shorter wavelengths have more

energy that plants are able to use, which increases the rate of photosynthesis excluding green light because green is

the color of chlorophyll a and b so therefore can only be

partially absorbed.

PredictionAll colors of light (clear filter) will have the greatest number of disks rise because

all colors of light are available for photosynthesis. Of the single colors, blue will

have the shortest wavelengths of the colors we are testing, so the greatest number

of infiltrated leaf disks will rise using the blue filter. Green will have the least

amount of leaf disks rise because plants reflect green light, but there will still be a

small amount that rise because chlorophyll a and b enable plants to absorb some

green visible light.

Experimental ControlThe experimental control for this experiment is the clear cellophane filter that we placed over the light. This can be considered as the control for this experiment because it contains all of the colors of light.

Procedure (the leaf disks) 1. A 250 mL graduated cylinder was filled with with 200 mL of water. 2. A scoopula was used to measure the proper amount of baking soda, which

was then added to the water.3. Three drops of dish soap were added to the mixture using a pipette, and it

was stirred until all solvents were completely dissolved.4. Using a hole puncher, 12 leaf disks were made from a spinach leaf that were

placed into the bottom of a syringe.5. The leaf disks were infiltrated with the mixture and moved from the syringe

into a plastic cup.6. More solution was poured into the cup so it was about halfway filled.

Procedure (the light set up)(Set up simultaneously as leaf disks were prepared) 1. The cellophane filter was taped onto the silver bowl

surrounding the light bulb (the same light was usedfor every trial).

2. Using the clamp, the light was secured in the cabinet.3. After the light was plugged in and turned on, the leaf disks would be quickly

placed underneath the light (the same distance from the light in each trial).4. The 15-minute trial began as soon as the cabinet door was closed.5. The cabinet door was opened quickly at 1-minute intervals to check and record

how many of the leaf disks had risen to the surface of the liquid in the cup.

Data Table

The following data table displays the number of leaf disks that had risen to the surface of the mixture by each minute of the 15-minute trials. The overarching trend is that the more energy from the light that was available for photosynthesis, the greater the amount of leaf disks rose.

The exceptions to this trend were green light and red light.

Time (minutes)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Red 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Yellow 0 0 0 0 0 0 0 0 1 1 2 3 4 5 6

Green 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1

Blue 0 0 0 0 0 0 0 0 0 0 5 8 10 11 11

Clear 0 0 0 0 1 1 1 2 3 4 6 7 9 11 12

Spinach Leaves at Top of Cup

GraphThe graph shows the rate of the leaf disks rising for all of the colors. As you can see, the clear filter had the most disks rise to the top by the end of the 15 minute trial while red had the least.

DiscussionWhen looking at the data there are many trends, and those trends also link to photosynthesis. In

our data, the clear filter had the most amount of leaf disks rise, and red the least. Through each piece of data, one can see how each color of light, with different wavelengths and energy, affects the rate of photosynthesis. It makes sense that the clear would have the most leaf disks rise, because the clear filter allows all colors of visible light through it, and therefore has the most light energy available for photosynthesis. Then, for the next portion of the data, the colors almost directly follow the light scale. Blue was the next to have the most leaf disks float, and that is because it has shorter wavelengths and therefore more energy. Then was yellow, which has longer wavelengths than blue, but shorter than the green, which is why our data clearly shows this. In addition, since the spinach leaf disks were green, they cannot absorb much green light and therefore cannot really use the green light to photosynthesize. However, the one part of the data that does not make sense, is that the green light had more leaf disks rise than the red light. Since red light can be absorbed by the spinach leaves, unlike green, red data must be the result of some error.

Possible Errors

The red cellophane trial was repeated three times, and no leaf disks had risen by the end of each 15-minute trial. This contradicted the prediction and hypothesis. A possible reason why that error may have occurred was because some of the different cellophane in the colored filters may have had different tints to them (therefore not allowing as much light to pass through). Not nearly as much light passed through the red filter as the blue, green, yellow, or clear. Perhaps tint of the cellophane could have affected light energy available for photosynthesis. This therefore affected our data by having no leaf disks rise for the red cellophane trials because not enough light could pass through.

ConclusionThe hypothesis was that the colors of light with shorter wavelengths have

more energy that plants are able to use, which increases the rate of photosynthesis excluding green light because green is the color of chlorophyll a and b so therefore can only be partially absorbed. In the experiment, the data mostly proved the hypothesis. Clear light increased the rate of photosynthesis the most, as was expected. Out of the colored lights, blue had the shortest wavelength and the fastest rate of photosynthesis. Green had only one disc rise which proves the prediction because green light did photosynthesize but very little. Yellow data also proved the prediction because its rate of photosynthesis was slower than blue and had shorter wavelengths. The only piece of data that contradicts the prediction was the red light data. This was a result of error due to the tint of the cellophane.

Conclusion (continued)To improve on this experiment, more leaf disks could be used to

demonstrate more specific differences between the different colors of light, as well as allow more time in the trials for the leaves to photosynthesize. Also, more trials of each color could be done to help weed out erroneous data and have more correct results. More filters could be used to test more colors of light such as violet or orange. Finally, if resources are available, the amount of light that is able to pass through each filters could be tested to ensure that all filters allow the same amount of light to pass through.

Thank You!