Absorbing Light Waves in Photosynthesis. Evan Bradley, Tara Popik, Ava Tillman

Transcription

1 Absorbing Light Waves in Photosynthesis Evan Bradley, Tara Popik, Ava Tillman

2 Question How do different wavelengths of light affect the rate of photosynthesis in leaves? spinach

3 Hypothesis/Prediction Prediction: If the spinach leaves are placed under blue or red light, the rate of photosynthesis will be faster than green light because chlorophyll a and b as well as several types of carotenoids are present in the spinach. This causes an absorption of energy from red and blue wavelengths which is used in photosynthesis. If the spinach leaves are placed under green light, they will cease to perform photosynthesis because green wavelengths are reflected by plants and not absorbed. Hypothesis: When spinach is in the presence of red or blue light, it will have a faster rate of photosynthesis compared to other wavelengths in the light spectrum due to the plants abundance of chlorophyll a and b as well as several carotenoids which help absorb red and blue wavelengths and turn them into chemical energy during photosynthesis.

4 Procedure First, 12 leaf disks were created with a hole punch. Then, a bicarbonate solution was made using a pinch of baking soda, a drop of dish soap, and approximately 25 ml water. The leaves were placed in the syringe and 1/3 of the syringe was filled with the bicarbonate and soap solution. A vacuum was formed using the syringe. Someone's finger was placed on the tip and the back of the syringe was pulled backward. This process was repeated approximately three times until the leaves sank to the bottom of the solution. After they were infiltrated, the leaves were dumped back into the cup containing the bicarbonate and soap solution. The cup was placed approximately 8 cm away from a light that was covered in clear cellophane. Every minute for 16 minutes, the number of leaves that floated to the top of the solution was counted and recorded. This entire process was repeated while covering the light with green, blue, and red cellophane.

5 Experimental Control The control for this experiment involved placing the leaf disks underneath the light covered with clear cellophane. This is an effective control because instead of radiating one specific wavelength, the clear cellophane would allow the light to radiate all of the different wavelengths of visible light. For the entire experiment, the control could be compared to as the ideal situation for a given plant to perform photosynthesis.

6 Data As time increases, more leaves rise. Out of the three colors/wavelengths tested, red light was the most effective with blue light trailing slightly.

7 Data Leaves Risen Minute Control Red Green Blue Total Count Total %

8 Discussion In this lab, the rate of photosynthesis under different colors and wavelengths of light was measured. In order to measure the rate at which photosynthesis occurs, the number of leaf disks that floated per minute was recorded. This method was used to measure the rate of photosynthesis. It is known to be effective, because the factor that allowed the leaf disks to float was the fact that they were producing oxygen, and since oxygen is a known product of photosynthesis, it can then be safely assumed that the leaf disks were performing photosynthesis Therefore, if more leaf disks rose during the allotted time, the rate of photosynthesis was quicker. Not all of the leaf disks rose at once, though, for some of the leaf disks had more direct access to the light source than others. From the data collected, it can be concluded that spinach leaves absorb red and blue light the best, showing that photosynthesis occurs at a faster rate when red or blue light is present compared to when green light was present. When the spinach leaves were exposed to the green light the rate of photosynthesis fell immensely and almost stopped completely. These results can be explained by understanding the way leaves absorb light.the spinach leaves contain chlorophyll a and b as well as several carotenoids which help absorb red and blue light wavelengths that they receive from the sun and turn into chemical energy during photosythesis. As for why green was not as effective as red or blue, this was due to the fact that spinach leaves reflect green light. Reflecting green light is what gives spinach its green color. Even though the desired results were produced, there is one unusual data point that did occur. Under the red light, during minutes ten to sixteen, a plateau was experienced, and no leaf disks rose. This is most likely simply due to the leaf disks access to the light. If all leaf disks had equal access to the light, the plateau would probably have been avoided.

9 Errors Possible sources of error in this lab include the spinach leaves exposure to small amounts of fluorescent light and the mass of the leaf disks. If the leaves were being exposed to small amounts of fluorescent light during the experiment, the data collected would be disqualified, for it would be impossible to draw valid conclusions without knowing what wavelengths were included due to the fact that the fluorescent light contains several different light wavelengths. This can be exemplified by simply using a prism with the fluorescent light and showing it true composition of several different wavelengths of light. At blame for this possible error would be the light bulbs in the classroom shining on the cup when it was being exposed to the green, red and blue wavelengths. This could have been prevented by shutting off these light bulbs or using some type of contraption to help block out those waves of light. The mass of the leaf disks not being uniform throughout would skew the results, for leaf disks with larger masses would require more oxygen to be produced in order to rise than ones with lower masses. Therefore, not all of the leaf disks would have had an equal opportunity to rise, since time was limited.

10 Conclusion The original hypothesis was supported by this experiment. It was originally stated that when the spinach leaves are placed under blue or red light, the rate of photosynthesis will be faster than green light because chlorophyll a and b as well as several types of carotenoids are present in the spinach. This causes an absorption of energy from red and blue wavelengths which is used in photosynthesis. This was supported by our experiment because red and blue light were the most effective when measuring the rate of photosynthesis compared to green light which was simply reflected by the leaves. For example, our data shows that red had 7 leaves float and blue light had 6 leaves float whereas green only had 5 leaves float. In conclusion, different wavelengths of light do affect the rate of photosynthesis because some wavelengths such as red and blue are absorbed and used by the plant whereas others like the green light are reflected.