| Explore | Outside our experiences in school, we knew that plants are eukaryotes that perform photosynthesis to fuel the metabolic processes needed for their growth. They took in energy from the sun and oxygen from the air to produce sugars and release oxygen. Within the classroom, we have discovered that the two major metabolic pathways of plants, photosynthesis and cellular respiration, are each comprised of numerous intermediate reactions. Different plants thrive under different conditions, but all plants photosynthesize most effectively with sufficient amounts of light, water, and carbon dioxide. We are interested in how plants respond to different wavelengths of light. For example, how will plants photosynthesize under red light? How will their rate of photosynthesis under red light compare to that under blue light? |
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| Research Question | We wanted to study the effect of carbon dioxide on photosynthesis. This was done by comparing infiltrated leaf disks in three solutions of varying carbon dioxide concentration and the amounts of floating disks in each sample (which correlated to their release rates of oxygen gas). The question expands our understanding of the topic because it demonstrates how the amount of carbon dioxide taken in by the plant affects its rate of photosynthesis. |
| Predictions | Some possible outcomes were: 1. the infiltrated leaf disks in all three solutions would float, 2. the leaf disks in the solutions with carbon dioxide would float, or 3. none of the leaf disks would float. We predicted result #2. Since all samples received an equal amount of light, water and number of leaf disks, the only difference between the solutions was the amount of carbon dioxide in the water. We figured that photosynthesis may only occur when light, water, and carbon dioxide are all present. Two out of three of the solutions had carbon dioxide, so we predicted that only the leaf disks in those two solutions would photosynthesize and subsequently float. |
| Experimental Design | We filled three cups each with 100mL of water and two drops of dish soap. In the first cup, labeled "water," nothing else was added. In the second cup, labeled "breath," a group member blew into the solution using a straw for 90 seconds. In the third cup, labeled "baking soda," 0.2 grams of 0.2% baking soda was added. We cut 36 small disks of spinach leaves with a straw. We then infiltrated them with twelve disks per syringe, for a total of three infiltrations (one for each solution). After infiltration, we placed each set of disks into the cup with their respective solution. We placed each cup 1.5 inches from the lamp and kept them there for 25 minutes. In our lab notebooks, we recorded the number of floating disks for each cup every minute. After the first 8 minutes of data collection, we swirled the solution every two minutes. |
| Conclusion | Along with light and water, carbon dioxide is required for photosynthesis to occur. After 25 minutes, 5 out of the 12 leaf disks in the baking soda solution floated, while none of the leaf disks in the water or breath cup floated. The results support our claim because the disks floating in the baking soda cup were exposed to sufficient amounts of light, water, and carbon dioxide, and the disks that did not float in the water cup were only exposed to light and water. A reason why the disks in the breath cup did not float may have been the lower concentration of carbon dioxide in the solution, as 90 seconds of breath may not have contained as much carbon dioxide as 0.2g of 0.2% baking soda. It would be reasonable to assume that after a longer period of time, some of the leaf disks in the breath cup may have eventually floated. To expand on the results of this experiment, we could analyze the variation in photosynthesis rates of leaf disks in solutions of differing concentrations of carbon dioxide (which can be varied by the amounts of baking soda added). |
| Investigation Theme | POS |
| Grade Level | High School Students (Grades 9,10,11,12) |
| School Name | West High School |
| Session | Fall 2017 |