| Explore | Plants use photosynthesis to convert light energy into chemical energy, which takes place in the chloroplasts. This takes place in two stages: light-dependent and the Calvin cycle. The light-dependent reaction uses energy from sunlight to split water, producing oxygen gas, protons, and high-energy electrons. The oxygen is released and the protons and high-energy electrons power the production of ATP and NADPH. This is then sent to the Calvin cycle, where the ATP, NADPH and carbon dioxide, produce sugars. Then sends ADP pi and NADP + back to light-dependent so the photosynthesis can continue. We learned in class that plants need light and carbon dioxide. We did this by seeing if the plant leaves float in different light and carbon dioxide levels. |
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| Research Question | How can changing the pH affect plant growth? We came up with this research question because one of our past experiments used pH to determine if O2 was being produced. This brought up the question if the pH of the solution that the leaf is in would affect the rate of photosynthesis. This question fits what we know about the topic as we know that if pH gets too high or low, structures can denature which would therefore stop photosynthesis. |
| Predictions | We believe when the plant is exposed to higher or lower pH, the plant will lower in rate of photosynthesis or stop within the plant. This would happen due to the change of the hydrogen ion gradient within the thylakoid causing the Electron transport chain and ATP synthase to slow or stop working. Which would cause the stop and or slowed production of photosynthesis. |
| Experimental Design | 1. Cut out 36 leaf disks from the spinach plant. 2. Get 3 cups and label one high pH, one low pH, and one neutral. 3. In the cup labeled high pH add water, sodium hydroxide, and baking soda. In the cup labeled low pH add water, sulfuric acid, and baking soda. In the cup labeled neutral add water and baking soda 4. Record the pH of each solution with pH testing strips. 5. Vacuum 12 leaf disks with a syringe filled with the corresponding solution until all sunk. Repeat this with the other two solutions. 6. Put all three cups under a light. 7. Record how many disks are floating or not floating every minute. The variables we are testing if amount of pH. We keep everything else about the experiment constant. |
| Conclusion | From our experiment, we found that the neutral pH solution had the highest rate of photosynthesis. In contrast, the higher and lower pH solutions had a lower rate of photosynthesis, with lower pH having the lowest rate of photosynthesis. The explanation for these results is that photosynthesis has an optimal pH of 7, and as the pH increases and decreases, the rate of photosynthesis lowers because it is not at its optimal pH yet, but nothing has denatured. This supports our claim that a pH of 7 yields the most effective rate of photosynthesis, and as it increases and decreases, the rate of photosynthesis decreases. A future experiment that could be done to expand on the results of this experiment is making the pH of the solutions even higher/lower to see at what pH the rate of photosynthesis stops because of denaturing. |
| Investigation Theme | POS |
| Grade Level | High School Students (Grades 9,10,11,12) |
| Teacher Name | Shirl Shawhan |
| School Name | Hunterdon Central Regional High School |
| Session | Fall 2023 |
| About this Project | The mentor and the mentees tried to communicate with each other by using plant jokes. The mentees cracked a plant related joke every time and the mentor complimented them on that. But then the mentor joined in the closing comments and cracked a joke themselves. -- SNEHANJANA CHATTERJEE, Liaison |
