How does intensity and wavelength of light affect photosynthesis?
Group Members: Natalie Mansergh, Emmy Nam, Ananya Somasekar, Amritha Somasekar
Photosynthesis: Photosynthesis is crucial for plants to carry out life. It starts with the penetration of light into the cell. Light is one of the most essential and mandatory predecessors to photosynthesis. The light reactions, which take place in the thylakoids of the chloroplast, use the light to excite its electrons. The excited electrons then make their way down the electron transport chain, where water molecules are split in order to bring the electrons to an even higher state of energy. The positively-charged H ion is used to form NADPH and ATP, which is then transported to the Calvin Cycle (light independent reactions). The two remaining Oxygen ions form O2 - which are the byproduct of the light reactions. This is why plants give off oxygen. At this point in time, the ATP and NADPH in the Calvin Cycle undergo processes that create CH2O (sugars).
Hypothesis: If we decrease the intensity of the light through covering the leaves with black paper, photosynthesis will cease; if we decrease the wavelength through covering the leaves in cellophane, the frequency of the wavelength will increase and therefore there will be more photosynthesis.
Materials:
- calendula (plant) - black paper - test tubes - pipettes |
- cellophane
- Lugol's iodine - petri dish - scissors - tape |
Procedure:
1. Cover 3 leaves in: cellophane, black paper, and none (control) 2. Wait 48 hours 3. Cut off experimental and control leaves, remove the papers 4. Roll up leaves and put into test tube; label 5. Extract chlorophyll with hot alcohol |
6. Rinse in water
7. Place in petri dish 8. Cover with iodine 9. Wait 1 minute, then remove leaf and place on paper towel 10. Observe and record observations in a data table, giving numerical value for color change |
Results:
Control - most chlorophyll
|
Cellophane - less chlorophyll
|
Black Paper - almost no chlorophyll
|
Iodine Test:
Control (None) Wavelength (Cellophane) Intensity (Black Paper) |
Qualitative Observation:
mostly green turned brown, okra color turned dark, dark brown |
Quantitative Observation:
1 4 5 |
Analysis & Conclusion:
In this lab, we learned how intensity and wavelength of light affects photosynthesis production. Our original hypothesis was that blocking light with the black paper would be detrimental to photosynthesis, while the cellophane would help the process. We thought that the blue cellophane would shorten the wavelength, and therefore make the light dependent reactions more active. We were proved wrong in this experiment. The control had the most chlorophyll, the cellophane had less chlorophyll, and the black paper had very little chlorophyll. While the change was not so evident in the cellophane covered leaves, the ones that had been wrapped in black paper shriveled up within the 42 hours of the experiment. From this experiment, we learned that leaves absorb red and blue pigments, reflecting green: the blue cellophane means that blue is the color being reflected, not absorbed. This hinders the photosynthesis process and explains our experimental results.
Reflection:
Our group worked extremely well together. We stayed on task the entire time, split up responsibilities evenly, and collaborated in a professional fashion. I thought that this particular lab was interesting and I learned from the results and our hypothesis. I did a similar project in fifth grade testing if brown leaves had chlorophyll as well, and we used alcohol to extract the green pigment in beakers; this experiment was unique because we then used an iodine indicator test. We would have liked to get more conclusive results on the iodine test; maybe if we had put it back in the test tube and boiled it, we could see the color change more clearly. Otherwise, this was a really insightful experience and we learned a lot about photosynthesis.