The Effects of Different Wavelengths of Light on the Rate of Photosynthesis

The effects of different wavelengths of light on the rate of photosynthesis

Introduction

This experiment was performed to investigate the effects of different wavelengths of light on the rate of photosynthesis. If a multiple colored film petri dishes are place under a 50 watt lamp, then the rate of photosynthesis will be greater for those with red, blue and clear film, than those with green and black film.

We believed the petri dishes with the red, blue and clear film would produce the best results of photosynthesis as compared to the petri dish with the green and black film. This is said because chlorophyll absorbs red and blue wavelengths of light and reflects green wavelengths of light. When referring to the light spectrum, red and violet are furthest away from green, and would be most absorbed by the leaf. White light is all the colors of the spectrum, and would have results similar to that of red and blue.

Below is a chart provided by Daniel Winik of Sidwell Friends School in Washington, DC. A similar experiment was done using Arabidopsis thaliana plants. The purpose of his experiment was Тto observe the effects of different wavelengths of light on the rate of photosynthetic rate in Arabidopsis thaliana plants.У

By using petri dishes with colored film, and spinach disks, we are allowing only certain wavelengths to pass through and show the rate of photosynthesis. If the experiment is done properly, it will provide us with the expected results. As the wavelengths are allowed to pass through the spinach disks will begin to float or remain the sunken at the bottom of the petri dish. The spinach leaves will float once enough O2 (a product of photosynthesis) has been accumulated.

If the hypothesis is supported, the petri dishes with the red, blue and clear film will provide the best rate of photosynthesis. The independent variable would be the wavelength of light and the dependent variable is the rate of photosynthesis measured by a percentage.

Materials

The materials needed for this experiment will consist of petri dishes with a variety of films. The colors for this experiment will be red, blue, green, clear, and black film, to cover the petri dishes. The experiment will be performed using spinach disks, which are spinach leaves that have circles punched out using a cork borer. There will need to be 20 spinach disks for each petri dish, totaling 100 spinach disks. All of the spinach disks will be placed in a beaker containing a bicarbonate solution. The beaker will then be covered by a rubber stopper, and hooked up to a water aspirator. A water aspirator will be used as a vacuum source to sink the disks. You will also need to pour 0.2% NaHCO3 into each petri dish, so it is about 2/3 full. An estimated amount of NaHCO3 would be 100 Ml. The petri dishes will then be placed under a 50 watt lamp, 25 cm for the base, for a time period of 20 minutes.

Results

The results can are expressed in the Table 1 shown below:

Wavelength Number floating Percentage

White 20 100

Red 18 90

Blue 6 30

Green 0 0

Dark 0 0

After the petri dishes had sat under a lamp for 20 minutes, the petri dish with the clear film had the best results. This is followed by the petri dish with the red film, then the petri dish with the blue film. The petri dishes with the blue and black film had shown no photosynthesis took place. Graph 1, shown below, shows the results of the effect of different wavelengths on the rate of photosynthesis

Discussion

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