Our experiment tested which color (red, blue, green) would influence the plant to produce the most amount of photosynthesis. There are four main photosynthetic pigments found in the chloroplast of the plant called chlorophyll a, chlorophyll b, xanthophylls, and carotenes. All these pigments absorb light and possibly utilize the light energy in photosynthesis. Light energy is essential for photosynthesis. An initial experiment showed that all the pigments at peak absorbance showed violet/blue light at the highest level, orange/red light as the second highest, and yellow/green having the lowest level of absorption. We hypothesized that photosynthesis was affected by the light absorption rate.
Plants utilize the process of photosynthesis to convert solar energy into chemical energy to produce cellular respiration. The process of photosynthesis uses the energy of sunlight, which is then absorbed into different pigment types to help the cyclical functions that eventually create atmospheric oxygen. In this experiment we asked how different colors of light effect the rate of photosynthesis. The experiment attempted to see how blue colored and red colored lights affected the rate of photosynthesis. It was hypothesized that because plants absorb more red light, then we predict plants in red light should have a higher rate of photosynthesis when compared to plants in blue. The hypothesis was tested by taking the leaves of a live plant and placing the leaves in a flask. A carbon dioxide gas probe was then placed in the flask to test if the levels of carbon dioxide changed. The independent variable was the color of light and the dependent variable was the rate of photosynthesis in change in levels of carbon dioxide per minute per gram. The change in carbon dioxide levels were proportional to the rate of photosynthesis. Thus red light and blue light was placed upon the flasks of leaves for a total of thirty minutes. The first and last ten minutes the leaves were set in the light and the second ten- minute increment the leaves were in the dark. The second ten minutes was to see if carbon dioxide levels decreased thus to control the cellular respiration. The results show in comparing the carbon dioxide levels that the p=value is .36 meaning there was no significance in the comparison. Therefore the different wavelengths in light made no extreme difference on the rate of photosynthesis. In comparison to other experiments done by others the results were much the same finding that neither light wavelength affected the rate of photosynthesis. The experiment was done with a limited amount of time and the leaves were most likely dead by the end of the experiment. A better hypothesis would be to see how the wavelengths of different colored lights like yellow and green affect the rate of photosynthesis. The use of more live plants would help obtain better results also.
These results may seem perplexing if we take the adage 'a photon is a photon' to be correct, and the color of light (or more correctly, its energy level) does not make a difference in photosynthesis (which is true.)
Results of testing show there are clear differences in the rate of photosynthesis when light sources of different hue (or color) are used. See Figure 25.
The standard method for determining light requirements for corals' zooxanthellae has been examination of absorption characteristics of photopigments such as chlorophyll , chlorophyll etc. (good) or action spectrums (better). Both are not without problems. Absorption characteristics are usually based on pigments extracted in solvents. Spectral characteristics shift slightly according to the extraction solvent used, and photopigments, when combined, also change these characteristics slightly. A better way is to examine the action spectrum of zooxanthellae isolated from a stony coral. This is usually done with a monochromator, where a beam of pure color (hue) illuminates a culture of dinoflagellates and a reaction is determined (such as oxygen evolution). A chart of wavelengths versus reaction is then made. See Figure 1. This method also suffers from deficiencies - the two Photosystems (I and II) absorb light wavelengths with difference efficiencies, hence a monochromator might stimulate one photosystem, but not the other, and photosynthesis might not proceed efficiently (although 'spill-over' - also called State Transitions 1 or 2 - could perhaps overcome this problem - something very much in the discovery phase for zooxanthellae.) See Kirk (2000) for further details on action spectrums.
In addition, since the team used different lights for the different colors, the light intensity may have been unequal, also resulting in inaccurate data.
If we were to do the lab again, we would include a trials with more colors of the visible light spectrum such as orange and violet to get a more comprehensive and seamless set of data.
Realizing the fact that light intensity is another variable which may affect results, the team measured the intensity of the different color lights.
CONCLUSION AND CONCEPTS
During the experiment, some of the leaf disks would not rise from the bottom of the beaker.
Record or report findings.
Rate of photosynthesis (measured by ET50, time it took for 50% of the leaf disks to float up)
Color of light (wavelength of light)
Light intensity, temperature, bicarbonate concentration (0.2%), depth of bicarbonate solution, direction of incoming light, pH, amount of soap, size of leaf disk, type of plant
Ten trials for each color, however for each trial, a few disks did not float up.
Our results show that different color lights definitely does have a strong direct correlation with the rate of photosynthesis/growth of a plant.
LIGHT ABSORPTION IN PHOTOSYNTHESIS
Absorption spectra showing how the different side chains in chlorophyll a and chlorophyll b result in slightly different absorptions of visible light.
The plant responded to the different colored light as follows: The rate of photosynthesis was the most successful in white light, and more successful in red and blue lighting, than in green and yellow lighting systems.
Green or yellow light will have the slowest rates of photosynthesis because they are reflected by the pigments in the plant.
DESCRIPTION & ANALYSIS
SOURCES OF ERROR AND IMPROVEMENTS
In this lab experiment, the team examines how the rate of photosynthesis is affected by different light colors in the leafs.
If white light is a mixture of several wavelengths of colors and the chlorophyll in green leaves absorb energies from all visible light except green, then exposing white light to a green plants will result in the fastest rate of photosynthesis, followed by blue or red.
Therefor, the faster the rate of photosynthesis, the faster the leaves rises.
There are five matters that affect the rate of photosynthesis: light intensity, temperature, CO2, water, and the color of light in general.