Photosynthesis: An Essential To Life

Abstract

The purpose of this experiment is to gain insight about how photosynthesis occurs and when the process of photosynthesis is the most efficient. The hypothesis being tested in this experiment is: if the light is greater than 5000 Lux, then the rate of photosynthesis will increase as the Lux of light increases. The way to test this hypothesis is to put leaves in light and measure the oxygen output of the leaf. The hypothesis that is stated above is found in this experiment to be true, in which photosynthesis is more efficient with more light intensity (within the range that has been tested). There is never a time when photosynthesis is not needed for life to continue on earth. This study has proven that plants can be put in specific environments in order to grow more efficiently and healthier as long as they are in an optimum environment.

Introduction

Photosynthesis is critical to life here on planet earth. Life on earth heavily relies on the process of photosynthesis. Practically all food derives from photosynthesis, one way or another. For example, if a human were to eat beef, the cow that that beef came from grazed on grass, and grass depends on photosynthesis for its own life. Photosynthesis is the process that plants take part in. In this process, light energy is being converted into chemical energy, which is a super-efficient process; but how efficient is it, and at what amount of light intensity, or lack thereof, is photosynthesis the most efficient? Photosynthesis has a chemical equation of 6 CO2 + 12 H2O + Light Energy C6H12O6 + 6 O2 + 6 H2O. Therefore, one way to know how efficient the photosynthesis is occurring is to measure the amount of oxygen being is being released since oxygen is one of the products of a photosynthesis reaction. There are two types of reactions that photosynthesis undergoes, and those are: light dependent reactions and light independent reactions, or Calvin Cycle. Light dependent reactions change light energy from the sun to chemical energy, and light independent reactions uses that chemical energy which helps push the synthesis of sugars. Light dependent reactions occur on the thylakoid membranes. While light independent reactions occur at the same time as light dependent reactions, light independent reactions occur in the stroma of the chloroplast. In this experiment, the amount of light will be measured in Lux, which is equal to 1 Lumen/m2. With all of that being said, the hypothesis that is being tested is as followed: if the light is greater than 5000 Lux, then the rate of photosynthesis will increase as the Lux of light increases.

Materials and Methods

In this lab, the first step is to calibrate the oxygen sensor and probe. This sensor will be used to measure the outputs of oxygen, which will tell us the rate of photosynthesis in ppm O2/s. The next step in this experiment is to assemble the gas monitoring chamber, which is the site in which data will be collected.

In assembling the gas monitoring chamber, the first step is to fill the 5mL serum vial with tap water. The second step is to close the vial with the gray rubber septum that has a hole in the middle of it. The third step is to choose a leaf that looks well nourished; put the leaf through the gray septum with the stem leading first, and make sure the stem is slightly dipped into the water. The next step is to carefully slide the serum down the cylinder until the serum is resting on the bottom. Turn the cylinder upright, and make sure the leaf is still placed in the serum. The next step is to add approximately 3 mL of sodium bicarbonate to the bottom of the cylinder, outside of the serum vial; this serves as a source of carbon dioxide because it is needed as an input in the photosynthesis chemical equation. The next step is to place the yellow cover with a hole in the middle of it on top of the cylinder, and make sure it is sealed well. Next is to insert the oxygen gas sensor probe through the yellow cover and into the cylinder. Depending if the goal is to see what the rate of photosynthesis would be with no light or with light would decide if aluminum foil is needed to cover the cylinder up. If the control is being tested, meaning no light, then there needs to be aluminum foil wrapped around the cylinder to prevent light from coming in.

The next step in the process is to be prepared to collect data. Do this by turning on the LabQuest2 tablet; after turning it on, change the duration to 300 seconds.

After doing those steps, the sensor will collect data by way of the probe. For this experiment, the lamp needs to be the right length away from the cylinder, depending on what lux is being tested. The lamp will then be turned on. The leaf needed to be getting as much light as possible. The way to make sure of that is to use a piece of paper and look at the shadow on the paper; wherever the shadow is the biggest, that is where the leaf is getting the most light. The leaf was then left in those conditions for approximately 10 minutes so the leaf can become acclimated to the climate. Then, the green button on the bottom left of the oxygen sensor should be pressed to begin collecting data which will take 300 seconds. The screen of the sensor then changes to the data being plotted in real time. The graph stops calculating after 300 seconds.

The last thing done in the procedure is storing the files off of the sensor onto a flash drive, and then uploading them to a computer for data analyzation.

Results

In this experiment, the goal was to see what amount of light caused photosynthesis to be most effective. The stated hypothesis is “if the light is greater than 5000 Lux, then the rate of photosynthesis will increase as the Lux of light increases.” This means that as the amount of one lumen/m2 (lux) increases, the rate of photosynthesis will continue to go up, as lux goes up. Looking at figure 1 below, notice that the 5000 lux experimental is much lower than all of the other graphs, and this is because there was a much less amount of light at such a far distance hitting the leaf, causing the input of light energy in the chemical equation of 6 CO2 + 12 H2O + Light Energy C6H12O6 + 6 O2 + 6 H2O to be much less than the other amounts of light. Notice that the 10,000-lux control actually has a higher rate of photosynthesis than our experimental, which is hard to understand because control means no light, which is done by covering the cylinder in aluminum foil. Notice how the 15,000-lux experimental has the highest rate of photosynthesis, which supports the hypothesis, because it has the greatest about of light at the closest distance, and it also has the highest rate of photosynthesis. This is not a coincidence due to the fact that the amount of light energy is greater in the 15,000-lux test than any other test.

The results overall do support the hypothesis. As the lux increases, the rate of photosynthesis increases. Although the 10,000-lux control had a greater rate of photosynthesis than the 10,000-lux experimental, both were still greater rates than the 5,000-lux tests. The 15,000-lux tests both were conclusively greater than the 5,000 or 10,000-lux tests. These tests revealed that as the amount of lux increases, so does the rate of photosynthesis. 

Discussion

The results of this experiment unanimously supported the hypothesis that was made. The hypothesis was stated as “if the light is greater than 5000 Lux, then the rate of photosynthesis will increase as the Lux of light increases.” One can see in the results that this in fact does hold true because as the intensity of light increases, so does the rate of photosynthesis. In light dependent reactions, photosystems which are located within the thylakoid will absorb the light and then use that energy from the light to create ATP and NADH, which are then used during carbon fixation by way of the Calvin Cycle, which takes place within the stroma of the chloroplast. This explains why the rate of photosynthesis is higher when the light intensity is higher which is due to the fact that light energy is required for photosynthesis. The only source of error that could have hinged on our findings is the fact that the control of 10,000 lux had a higher photosynthesis rate than the 10,000-lux experimental, which would contradict the hypothesis. In the next experiment, if given the opportunity, it would be nice to see if there is a certain lux at which photosynthesis will actually halt due to too much light intensity. This study shows that plants could be put into optimum environments for photosynthesis to occur, which would cause the plants to be much healthier than if they were outside where natural occurrences happen that can slow down the process of photosynthesis, such as a drought, which can help scientists and researchers know what to do in case of a severe incident in weather which may cause a food shortage and a need for vegetables that have to be grown in a greenhouse.

Literature Cited

• Lambers, Hans, and J. A. Bassham. Encyclopædia Britannica. Photosynthesis. June 13, 2019 [November 13, 2019]
• Raven, Peter H., K. A. Mason, J.B. Losos, S. R. Singer, S. Jansky, T. Duncan, G. B. Johnson. (2017) Biology, 11th Edition. McGraw-Hill Education, New York, NY.