How does the color of light affect the rate of photosynthesis in spinach leaves?

Grace Warznak Harkiran Arora Lawrence Mahle

Hypothesis and PredictionHypothesis: The lights higher on the light spectrum, like blue, would have the fastest rate of photosynthesis because the energy is the highest. The green light would have the slowest rate because the chlorophyll inside of the leaves reflects green light, so it would not be absorbed as much as the other colors.

Prediction: The blue light will have faster-floating leaf disks than the red, yellow, and green lights.

Experimental Control● A control experiment (no light filter) showed what typically happens with

normal light in photosynthesis● All of the lights had a filter of the same material so the results weren’t

affected.● The lights were kept at the same height above the cups so the amount and

intensity of the light was the same throughout each experiment.● The soap was the same brand throughout each experiment so the solutions

wouldn’t change.● The baking soda was the same brand throughout each experiment so the

solutions wouldn’t change.● Any leaves that were in the middle of floating to the top of the solution

when floating disks were being counted were counted as a floating disk.

Materials ● Sodium Bicarbonate● Dish soap● 1 pipette● 2 plastic cups● 5 cellophane light filters

(red, yellow, green, blue, clear)

● Spinach plant leaves● Hole puncher● 2 10ml disposable syringes

○ Without needles● Stopwatch● Light source (lamps)● Ruler

ProcedureThe first part of this lab was making the bicarbonate and soap solution. A pinch of baking soda and water (about 6 cm deep) was added to a cup and stirred. A drop of liquid soap was added to the solution and stirred, with little to no studs forming. The solution was then divided into two cups. Next, the light filter was taped beneath the light bulb. This was done to get different colored lights. The next part was making the leaf disks. Enough spinach leafs were selected to make 12 leaf disks per cup. Using a paper single hole puncher, the spinach was punched and many leaf disks were made. In order to make the leaf disks float, the gases inside were removed by infiltrating them with the bicarbonate and soap solution. For this part, the plunger was removed from the syringe and 12 leaf disks were poured into the barrel of the syringe. The plunger was carefully placed back into the syringe. The tip was then placed into the bicarbonate and soap solution and some of it was pulled up until the syringe was ⅓ full.

Procedure ContinuedThe syringe was then held with the tip upwards and the open tip was then covered with a finger. The plunger was pulled back, creating a vacuum. This pulled the gas out of the leaf disks and replaced it with the bicarbonate and soap solution. This was done until all the leaf disks sunk in the solution and were ready for testing. The leaf disks and solution were then put back in the cup. The cup was placed under the light and the number of leaf disks floating were counted and recorded at one minute intervals for 25 minutes. Once all the disks were floating or when 25 minutes were over, the next test was completed.

Data TableNumber of Floating Leaf Disks per each Color of Light (Round 1)

Number of Floating Leaf Disks per each Color of Light (Round 2)

Time (minutes)

Blue Red Green Yellow Clear No Light Color Blue Red Green Yellow

1 0 0 0 0 0 0 0 0 0 0

2 1 0 0 0 0 0 0 0 0 0

3 1 0 0 0 0 0 0 0 0 2

4 3 0 0 5 0 9 0 10 1 7

5 5 2 0 5 0 10 0 10 1 8

6 6 9 0 5 0 11 0 11 1 9

7 8 10 0 5 0 12 1 11 2 9

8 8 10 2 5 0 - 1 12 2 9

9 9 10 2 6 0 - 1 - 2 11

10 9 10 2 7 0 - 1 - 2 11

Data Table ContinuedNumber of Floating Leaf Disks per each Color of Light (Round 1)

Number of Floating Leaf Disks per each Color of Light (Round 2)

Time (minutes)

Blue Red Green Yellow Clear No Light Color Blue Red Green Yellow

11 10 10 5 7 0 - 1 - 2 11

12 10 11 6 7 0 - 2 - 2 12

13 11 11 8 9 0 - 2 - 3 -

14 11 12 10 10 0 - 2 - 3 -

15 11 - 10 10 0 - 3 - 3 -

16 11 - 10 11 0 - 3 - 4 -

17 11 - 10 11 0 - 4 - 4 -

18 11 - 10 11 1 - 5 - 4 -

19 11 - 10 11 1 - 5 - 4 -

20 12 - 11 12 1 - 6 - 5 -

Data Table Continued

Number of Floating Leaf Disks per each Color of Light (Round 1)

Number of Floating Leaf Disks per each Color of Light (Round 2)

Time (minutes)

Blue Red Green Yellow Clear No Light Color Blue Red Green Yellow

21 - - 11 - 1 - 10 - 5 -

22 - - 11 - 1 - 10 - 5 -

23 - - 11 - 1 - 11 - 7 -

24 - - 11 - 1 - 11 - 8 -

25 - - 11 - 1 - 12 - 8 -

Graph- Round One

The light without a color filter had the leaf disks that floated the fastest. The red light was the fastest filtered light, and the blue and yellow filters ended at the same time. The green light and the clear filters never made all of the disks float.

Graph- Round Two

The lights that were higher on the electromagnetic wave spectrum, like the blue light, had the leaves float slower. The lights on the lower end of the spectrum, like the red light, had faster-floating disks. The only exception was the green, where not all of the disks floated.

DiscussionAs shown by the data, the light without the filter was overall the most successful. This is because the leaf disks were being hit by light directly and there was nothing blocking the light that would make the rate of photosynthesis slower. This made the light have a shorter, more energetic wave, exciting the electrons in the second photosystem more quickly. Because the experiment was done two times, some trends were noticed. It was observed that the red light showed the fastest rate of photosynthesis of the filters. It was decided that this happened because the light seemed to be the brightest and light could easily get to the leaf disks.

Discussion (cont.)When the brighter lights were used, the rate of photosynthesis was faster because the intensity of the light was greater. One unusual piece of data that was noticed was the clear filter. It worked far slower than the other filters since only one disk floated. It was thought that this would work the fastest if not almost the same way as it did with the control (no filter). This may have been because the clear filter caused the angle that the light hit the leaf disks to be off, though there was no true reasoning or explanation behind this.

Experimental Errors● The amount of soap used in each solution was not measured

exactly the same every time because different pipettes were used, so some of the solutions may have had different amounts of soap.

● The amount of baking soda was not measured precisely, so the solutions may have had different amounts of baking soda.

● The filters may have had different intensities, so the results could have slowed down or sped up, depending on the intensity.

ConclusionThe hypothesis was that the lights higher on the light spectrum, like blue, would have the fastest rate of photosynthesis because the energy is the highest; the green light would have the slowest rate because the chlorophyll inside of the leaves reflects green light, so it will not be absorbed as much as the other colors. The first half was proven wrong by the experiment. The experiment showed that the control (no filter) and the red light worked the best. This is because of variables that were not accounted for when the hypothesis was created. The non-filtered light shone the clearest, most intense light as there wasn’t a cover. The red light was also successful because the filter was probably less thick or dark/intense than the other filters. The second half of the hypothesis was proven correct. The green light was the least successful because chlorophyll makes the leaf green, so most of the green light is reflected to make the leaf that color. This means the green light was mostly reflected instead of absorbed.