Effects of Green and Blue Light on the Rate of Photosynthesis - Lab Report Example

Effects of Green and Blue Light on the Rate of Photosynthesis Group: Effects of Green and Blue Light on the Rate of Photosynthesis Abstract This paper covers two experiments on photosynthesis; the first one investigates whether a positive rate of net photosynthesis depends on light levels while the second one establishes other factors that affect photosynthesis. Introduction Photosynthesis is the process through which green plants, algae, and cyanobacteria convert the sun’s energy into chemical bond energy of organic molecules that it consumes as food. On the other hand, respiration is a series of reactions that convert the energy in the bonds of the organic molecules into adenosine triphosphate (ATP) molecules that plants use to power their cellular activities. Whereas photosynthesis occurs in the chloroplasts, respiration takes place in the mitochondria. Both the chloroplasts and mitochondria are located in the leaf; hence the two processes may occur simultaneously, working against each other. This can be represented by the chemical reaction below: Photosynthesis combines carbon (IV) oxide from the atmosphere with water to produce energy (carbohydrates), which when broken down by transpiration yields water, carbon dioxide, and energy (ATP). Background Since photosynthesis and respiration occur simultaneously, the amount of oxygen generated by the former is cut back by the amount the former consumes. The difference between gross photosynthesis and the amount of oxygen consumed during respiration is referred to as net photosynthesis. This experiment aims to establish the dependence of net photosynthesis on light levels. Raised Question The experiment raises the question of whether or not net photosynthesis depends on the light levels supplied during photosynthesis. Hypothesis Under blue light the photo respiration will be faster than under green light. Prediction If the more leaf disks exposed to blue light float at a rate faster than those exposed to green light, then photo respiration is faster under blue light. The two experiments were carried out using similar materials, although there were a few variations. There were two independent variables in both cases: green and blue light was used. The dependent variable was the rate of photorespiration: the higher the respiration rate, the lower the net photosynthesis. Experiment 1 Materials The materials used in the first experiment were: Leaves (English Ivy) Paper punch Blunt probe Eight 100 ml beakers Bicarbonate solution Infiltration solution 10 ml syringes Cheese cloth Source of light (normal) Stop watches Ruler Calculator Ice bath Blue and green color filters (four of each) Refrigerator Graduate cylinder Weighing paper Method The first experiment was conducted using the following procedure: Each group cut 10–12 leaf disks from the English Ivy leaves using the paper punch over the weighing paper. This was done to ensure that all the disks are of uniform size. Only those with no tissue damage (jagged edges) were used in the experiment. The next step involved using the syringes to drive out air from the leaf disks. This was done removing the plunger and inserting the disks in the syringe. After this the infiltration solution was added into the syringe up to the 6 ml mark, and the plunger inserted and depressed to remove air. We then covered the tip of the syringe with thumbs and drew the plunger back to create a vacuum for five seconds. The thumb was removed, and the plunger depressed severally until the leaf disks sank. This procedure was repeated to produce four sets of leaf disks for the four replicas of the experiment, hence bringing the sample size to 80. In conducting the actual experiment, each group added 50 ml of bicarbonate buffer solution into the cylinder and then emptied the infiltration solution and leaf disks from one syringe into the beaker. We then added the rest of the bicarbonate solution into the reaction beaker, discarding leaf disks that did not sink. This was done using 8 beakers, each containing 10 disks; 4 for blue light, and 4 for green light. The beakers were laced with foil and could only get light from the bottom where the blue and green color filters were placed. Measurements were then taken, with the percentage of disks that floated being tabulated against time for values between 10% and 90%. The measurements were taken after every minute. Each group repeated the experiment four times, found the average, and submitted its data to the class to form the class data. Results The graphs below show a comparison between the green light and blue light. [Figure] 1: From the 1st experiment the leaf disks in green light record a faster time than those in blue light. [Figure] 2: Based on the 1st experiment; from 10% to 90% leaf disks’ averages (4 beakers in green light and the other 4 beakers in blue light) are recorded. The observation implies that the leaf disks in green light are photosynthesized more rapidly than those in blue light. [Table] 1: Table showing standard deviation in Experiment 1 The leaves in the beakers with green light took a shorter time to rise than those in the beakers with blue light. Those in green light took half as much time for them to rise compared to those in blue light; it took 16.5 minutes in green light and 33 minutes in blue light. The t-test below is carried out on the hypothesis using the results of this experiment. The sample size used is 40 for both blue and green light, the confidence level at 95%, and with 78 degrees of freedom. The critical t-value with 5% chance at 78 degrees of freedom is 1.6646, which is less than the calculated t value; hence we adopt the hypothesis: Under blue light the photo respiration will be faster than under green light. Discussion The faster rising in green light than blue light indicates that air is filling the leaf disks at a faster rate in the green light than the ones with blue light. This air filling the leaf disks comes from the processes of photosynthesis and photorespiration (Lambers & Balears, 2010). These results, therefore, suggest that the rate of photorespiration is higher under green light than blue light. According to this experiment, net photosynthesis is lower in green light than blue light. Experiment 2 Materials and method The second experiment used most of the materials utilized in Experiment 1, albeit in fewer quantities than in the 1st experiment. They included two head light stands, 1 green and 1 blue filter. The sample size used in this experiment was 20; there were 20 leaf disks and two beakers. As opposed to the first experiment, the beakers were not covered in foil. They were covered with colored, circular filters: blue and green. Although this experiment was not replicated, it also recorded the percentage of leaf disks that floated against time, ranging from 10% to 90%. Results The results of the experiment can be summarized in the graphs below: [Figure] 3: Based on the 2nd experiment, the 90% leaf disk under blue light is photosynthesized more rapidly while the 90% leaf disk under green light is photosynthesized at a slower rate. [Figure] 4: Based on the 2nd experiment, overall, the leaf disks under blue light are rising faster than under green light. [Table] 2: Table showing standard deviation in Experiment 2 The leaf disks in the blue light rose at a faster rate than those under the influence of green light. It took 13 minutes for the disks under the influence of blue light, and only 10 minutes for 90% of those exposed to blue light. A t-test based on this study yields the results below: Discussion The critical t-value with chance > 95% at 18 degrees of freedom is 2.1009. This value is less than the tabulated t-value (2.212); hence, we adopt the hypothesis. Therefore, it is correct to state that photorespiration is faster in blue light than in green light. This implies that blue light yields a photorespiration rate higher than green light does, hence the higher rate of carbon dioxide gas production. Experiment 2, therefore, suggests that blue light results in a lower net photosynthesis than green light. References Lambers, H., & Balears, U. I. (Eds.). (2010). Plant respiration: From cell to ecosystem (advances in photosynthesis and respiration). New York, NY: Springer Publishing. Read More