| Explore | Outside of school we have learned that plants need fertile soil, a good source of water and carbon dioxide, and light in order to survive. In class we learned that plants use photosynthesis to create an energy source for themselves known as glucose. The equation for photosynthesis is 6CO2+6H2O—>C6H12O6+6O2 and chloroplasts are the site of photosynthesis. There are two main parts of photosynthesis: light reactions and the Calvin cycle. Some questions that interest us are: Where do plant’s masses and growth come from? Does the rate of photosynthesis change as a plant grows or does it stay consistent? How does climate change affect plants and plant growth? |
|---|---|
| Research Question | How does temperature affect photosynthesis? We came up with this question because we have studied elodea with different levels of light and CO2. With this experiment we were most interested to see how temperature (another environmental factor) affected the amount of photosynthesis over time in an elodea plant. This question fits because we have been learning about different environmental factors that affect photosynthesis. |
| Predictions | There are three possible outcomes of this experiment: the highest amount of photosynthesis could be from the low temperatures in the refrigerator, high temperatures from the heat lamp, or room temperature from being in the classroom. We predict that the elodea plant with the heat lamp will have the highest amount of photosynthesis take place because tropical rainforests, which have high amounts of plants and photosynthesis, typically have more tropical and hotter temperatures. The experiment that will result in the lowest rate of photosynthesis will be the elodea plant placed in the refrigerator because low temperatures slow down reactions, and photosynthesis is a reaction. |
| Experimental Design | For our first experiment, we wanted to use bromothymol blue as our pH indicator to determine how much photosynthesis took place. We measured levels of pH so that we could determine which temperature was ideal for photosynthesis. We kept baking soda constant so that we could give all of our solutions the same amount of carbon dioxide. Our data was recorded via a before and after data table of the pH’s for all 6 test tubes for the 24 hour procedures. Materials needed for experiment 1: 6 elodea plants, 6 test tubes for elodea plants, bromothymol blue, dissolved oxygen probe (to measure rate of dissolved oxygen), heat lamp, baking soda, tablespoon, refrigerator, lamp for refrigerator, lamp for room temperature, graduated cylinder (to measure 50 mL) Our procedure was as follows for the first experiment: 1. Get 6 elodea plants the same length and put them in the 6 test tubes. 2 labeled cold, 2 labeled hot, and 2 labeled room (for room temperature). 2. We poured 50mL of bromothymol blue into the test tube so that the elodea plants were covered. 3. We then put ¼ teaspoon of baking soda in the test tubes (to play the role of carbon dioxide) and stirred lightly. 4. We used a dissolved oxygen meter to measure the levels of dissolved oxygen in the 6 test tubes. 5. Afterwards, we took 6 2x2in parafilm sheets and stretched them so that they would cover the top of the test tube. 6. Place each set of two tubes in each of their locations (room under regular lamp, refrigerator regular lamp, or heat lamp) 7. Leave in locations for 24 hrs then uncover, and stick pH paper in the test tubes For our second experiment, due to our inconclusive results in the first experiment, we used solely water and baking soda to test the difference in pH before and after being in different temperature conditions. Materials needed for experiment 2: 6 elodea plants, 6 test tubes for elodea plants, distilled water, strips of pH paper, heat lamp, baking soda, tablespoon, refrigerator, lamp for refrigerator, lamp for room temperature, graduated cylinder (to measure 50 mL) The procedure for the second experiment was: 1. Get 6 elodea plants the same length and put them in the 6 test tubes. 2 of them are labeled cold, 2 labeled hot, and the last two labeled room temp. 2. Pour 50mL of spring water into each test tube covering the elodea 3. Then put ¼ teaspoon of baking soda into the water with elodea mix and stir lightly until dissolved 4. Use pH paper to determine pH levels in the test tubes. 5. After this place a 2x2 inch parafilm sheet on each of the 6 test tubes until they fully cover the top 6. Place each set of two tubes in each of their locations (room under regular lamp, refrigerator regular lamp, or heat lamp) 7. Leave in locations for 24 hrs then uncover, and stick pH paper in the test tubes |
| Conclusion | Unfortunately our first experiment displayed inconclusive results. However, after redesigning some aspects of our experiment, we were able to conclude that hotter temperatures produce a higher amount of the complete reaction of photosynthesis. A possible explanation for this result is because higher temperatures typically speed up reactions to a certain extent. We collected the data that the pH of the heated lamp test tubes changed from a pH of 8 to 9 overnight. This suggests that the water became more basic due to the usage of CO2 from the baking soda that created carbonic acid in the water, which were ultimately reactants in the photosynthesis. The coldest temperature elodea plants did not experience any pH change, while the room temperature elodea plants experienced a pH change of 8 to 8.5 overnight. This shows that temperature does affect the amount of photosynthesis, and that hotter temperatures result in more photosynthesis to an extent. A future experiment that could be done to expand the results of this experiment would be to find the optimal temperature for photosynthesis. This would show us what higher temperature specifically creates the biggest amount of photosynthesis overnight with denaturing the plant. |
| Investigation Theme | POS |
| Grade Level | High School Students (Grades 9,10,11,12) |
| Teacher Name | Jennifer Sunderman Broo |
| School Name | Mariemont High School |
| Session | Fall 2023 |
| About this Project | This project deserves consideration for a Star Project award due to the group's exceptional determination and resilience in the face of initial setbacks. Despite obtaining no results in the first iteration of their experiment, the team reevaluated their approach and realized they could measure pH directly instead of using an indicator. They hypothesized that the indicator they were using was too dark to allow light to penetrate to their aquatic plant. The group's problem-solving and dedication to continuous improvement show that they were truly engaged in the scientific process. -- Jennifer Broo, Teacher |
