The Colored Effect On Photosynthesis

Abstract

Photosynthesis plays a big role in the environment in everyday life. This experiment was done to see if an environmental factor affected the rate of photosynthesis. Scenedesmus obliquus algal beads were used as the primary source to receive photosynthesis. For this experiment, two different colored lights were used to see if the color of light being absorbed changed the rate of photosynthesis. The results that were observed are that the algal beads with the red-colored light increased in pH faster than the algal beads with the green light. Looking at the visible light wavelength, the red-colored visible light is longer in wavelength than the green visible light. It can be concluded that different wavelengths affect the rate of photosynthesis.

Introduction

Photosynthesis is a process that uses energy from the sun and carbon dioxide and water to make sugar and oxygen (Kratz). There are two different phases of photosynthesis. One of the phases is a light reaction. This is the process to convert solar energy into chemical energy within the thylakoids of the chloroplast. The second phase is the Calvin cycle. This process is within the stroma of the chloroplast and it takes carbon dioxide and changes it into sugar. With photosynthesis, only autotrophs are capable of photosynthesis; this includes plants, protists, such as algae, and bacteria. The equation for photosynthesis is:

6CO2 + 6H2O + light (energy) → C6H12O6 + 6O2

Many different environmental factors affect the rate of photosynthesis. The environmental factors include the amount of light exposure, the color of the environment, the closeness of the light source, and the temperature of the environment.

For this experiment, an experimental question and hypothesis were formed. The experimental question is, would the color of light being used in this experiment change the pH of the algal beads? The hypothesis that is being tested is, if algal beads are placed under a red light, then the pH of the CO2 solution will increase. To execute this experiment, the environmental factor chosen is the color of the light affecting photosynthesis. This role affects the earth’s system by the chloroplast and pigments absorbing certain colors and reflects others. This is all determined by the wavelength of each color on the visible light spectrum. The affects aquatic life very differently than terrestrial life. For aquatic life, there is a barrier of water between the sun and the autotrophs. For terrestrial life, they get direct sunlight. Light affects the biological processes by being the basis of living organisms, it is the primary source of life; without light energy, sugar is not being formed. It also affects metabolic processes by breaking down the sugars and giving organisms energy. The color of light impacts photosynthesis organisms all the same. All organisms that use photosynthesis have chlorophyll which contains a green pigment. Any color besides green will increase the rate because green gets reflected. Different colored lights do not affect cellular respiration as much as it does to photosynthesis.

For this experiment, Scenedesmus obliquus was used. Scenedesmus obliquus is found in freshwater and is not capable of movement. It is in the genus Scenedesmus and is most commonly found. Scenedesmus obliquus can morph and form into different shapes so it is hard for scientists to determine what species it is. For this experiment, it is important to see if the color of light affects the rate of photosynthesis. To execute this experiment, two different groups of algal beads will be placed under two different colored lights and the absorbance and pH will be recorded to see in thirty minutes, which color light would increase the rate of photosynthesis.

Materials and Methods

This experiment is testing if colored light changes the rate of photosynthesis. First, seven Scenedesmus obliquus algal beads were placed into one cuvette and different seven algal beads were placed into a second cuvette. Next with a serological pipette, two milliliters of carbon dioxide solution into each cuvette. The cuvettes were next placed into the spectrophotometer separately and the initial absorbance and color of each cuvette were recorded. With two different lamps, white pieces of paper were placed on the table, under the light for a lighter background and more accurate results. With the lights off, one cuvette was placed under one lamp, labeling it lamp A, and the second cuvette was placed under the second lamp, labeling it lamp B. Each lamp had a white light bulb for accurate results. One piece of red cellophane was placed on top of the first cuvette under lamp A and one piece of green cellophane was placed on top of cuvette two under lamp B. Once the setup was ready, both lamps were turned on at the same time and a timer was started. Every five minutes for thirty minutes, the absorbance and color were recorded. To record the absorbance, each cuvette was placed individually into the spectrophotometer and the absorbance was recorded in nanometers. To record the color, looking at the CO2 solution, see what color it looks like compared to the pH strip. Once each absorbance is recorded, the cuvettes go under the lamp again. This was repeated six times until thirty minutes were completed.

Discussion

After this experiment was completed, it was clear to see that the red light had the most amount of photosynthesis done to the CO2 solution. Photosynthesis occurred in both of the solutions with each different color of light. Cellular respiration did not occur because blue light was not present. Red and blue light display different changes in the chlorophyll than other colors on the visible light spectrum (Giese). Knowing that chloroplasts accept red visible light and reflect green light, helps by making the hypothesis correct. The hypothesis of the experiment was, if algal beads are placed under a red light, then the pH of the CO2 solution will increase. This was proven to be correct because the pH and absorbance both increased in the red light more than in the green. These results, in the real world, can help understand what light can do for photosynthesis. It can help to know that the color you see on organisms is because with all the visible lights shining on an object, the color that is being shown is the color that the organism is not accepting. During this experiment, there were problems with putting the cuvette into the spectrophotometer. The timer was never stopped so when testing the absorbance, the light was not being shown and it delayed the photosynthesis process. If this experiment would be done again, different colors would have been chosen. Since it is already known that green does not get absorbed, a different color would show different results. If things were to be added, a longer period would have been done to see the full potential of the photosynthesis and the pH would become more basic.