Factors That Affect Photosynthesis
September 18, 2014
Purpose: The purpose of this lab was to observe different situations with light intensity and wavelength of light can affect the process of photosynthesis. We also tested whether different chloroplast types are more efficient in certain environments with light by measuring the production of starch.
Hypothesis: If we decrease the intensity of the light, the photosynthesis process won't be as efficient because chloroplast needs enough light in order to function. If we decrease the wavelength by reflecting the blue light, the photosynthesis will be less productive because the plant won't be able to absorb the blue visible light and can only use red light for photosynthesis.
Materials: Green plant leaves, Red plant leaves, Black construction paper, Blue cellophane, Scissors, Iodine, Test tubes, Alcohol, Petri dishes, Pipets, Tape, Paper towels, Tweezers, Fume chamber, Hot plate
Procedure: First, we covered three selected plant leaves with black paper and three other leaves with cellophane to manipulate the intensity or wavelength of the light. We also kept several leaves of the same plant exposed to provide a baseline for our test results. After waiting forty-eight hours, while the plants rested under heat lamps, we then cut off the plant leaves and placed them into labelled test tubes. We also tested different types of chlorophyll separately by cutting different colored pieces off of a plant. The outer part of the leaf was green and was placed into a test tube and the inner part of the leaf that was red was placed in another test tube. Using a hot water bath, the chloroplast was extracted from the leaves using alcohol; this was to make it easier to visualize the color changes while testing starch. We then placed the leaves in petri dishes after rinsing the alcohol off and covering the plant in iodine. After one minute of waiting, we then observed color changes and recorded our results. Black to the fuchsia.
Color Changes Testing for Starch
Grading Scale: 1- Little to no reaction to 5- Great color change
Grading Scale: 1- Little to no reaction to 5- Great color change
Leaf Situation
Color Change Quantitative Result Observations (Before Chloroplast Extraction) |
Original Leaves
Stayed mostly green; Not much change 1 Felt sturdy and was a brighter green color |
Black Paper
Dark purple; Black 5 Shriveled up and dead leaves; Soggy texture |
Cellophane
Dark brown; Lighter brown spots in middle 4 Soggy leaves; Not dead yet |
Red Leaves
Dark brown; Entire leaf changed equally 4 Bigger than green leaves; Inside portion of leaf |
Green Leaves
Light brown; Redish shade 2 Smaller leaves located near base of plant; Outlined red parts |
Conclusion: Our results did not match our hypothesis or the expected outcome. Theoretically, our results should have confirmed our hypothesis as correct, but all of our tests were the exact opposite of the desired result. We labelled each container very accurately and distinctly and ensured that the variables were divided properly. However, one component of our experiment was obviously flawed because the results showed inconclusive data. The black paper was supposed to show the least amount of starch because the decrease of intensity of light should have slowed the process of photosynthesis. The blue cellophane reflected the blue visible light; therefore, the plant leaves only have access to light with shorter wavelengths. The decrease of options of light the leaves could absorb also slowed down the process of photosynthesis. These two reasons were supported by previous observations make before using iodine to test the starch content. We could view the physical changes that showed the original baseline test as a healthier plant that looked and felt stronger than the other tested variables. Even though the iodine test was not similar to predictions, our hypothesis could be correct because physical observations support our claim. If I were to redo this experiment, I would add more alcohol to the test tubes before boiling out the chlorophyll. This might allow for more of the coloring pigments to dissolve and make the iodine test clearer to read or compare.
Reflection: This project was personally challenging for several reasons. Although my group consisted of six people, myself included, it felt as though I was forced to continually encourage other group members to participate. The majority of gathering the supplies was done by me, along with the rinsing of leaves and petri dishes. Another issue this lab presented was the confusing results. Several people interpreted the incorrect results in many different ways and as a group, we couldn't decide on a final explanation for the unexpected observations. Despite these struggles, our group was very organized and clearly labelled everything to ensure no cross contamination occurred. These distinct labels were helpful while comparing the leaves after the finished experiment. Another positive point of our collaboration was the contribution of ideas for constructing the hypothesis. Even though there were two conflicting ideas for the hypothesis, people who sided with each side explain their reasons for supporting that idea. This made it easier to visualize different possible factors that could benefit or impinge on photosynthesis.