Abstract:
This experiment was performed to test the effect of different wavelengths of light had on photosynthesis. According to the results gathered we can say that if two plants are put under different lights, one green and one a normal light, that the plant under the normal light will perform photosynthesis at a higher rate than the plant under the green light. This experiment is important because it shows us the effect of different wavelengths of light had on photosynthesis. Introduction:
Photosynthesis is a two stage process. The first process is the Light Dependent Process (Light Reactions), requires the direct energy of light to make energy carrier molecules that are used in the second process. (Photosynthesis, 2010)The Light Independent Process (or Dark Reactions) occurs when the products of the Light Reaction are used to form covalent bonds of carbohydrates. In the Light Dependent Processes (Light Reactions) light strikes chlorophyll a in such a way as to excite electrons to a higher energy state.
In a series of reactions the energy is converted (along an electron transport process) into ATP and NADPH. Water is split in the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are used to make bonds in the Light Independent Process (Dark Reactions) (Photosynthesis, 2010). In the Light Independent reactions, carbon dioxide from the atmosphere is captured and is modified by the use of hydrogen to create carbohydrates (Raven, Johnson, Mason, Losos, & Singer, 2011).
In cellular respiration, the glucose that is made in photosynthesis is taken and converted into ATP which is used as energy to drive other functions done throughout the cells. The electromagnetic spectrum is special in the process of photosynthesis because it shows the different wavelengths of the different colors of light. This helps us find out what color(s) of light are absorbed best by plants for photosynthesis. Chlorophyll and carotenoids are the pigments inside the chloroplasts of leaves that absorb the light from the sun. There are two because chlorophyll reflect green light and can’t absorb the green light wavelength from the sun.
Carotenoids are in the leaves because they can absorb the green light so it is not wasted (Chlorophyll and Carotenoids, 2011). During the experiment performed in lab, my group was given the green wavelength to test. Our hypothesis was that the amount of leaves that rise under the light will be less than the amount that raised during the full spectrum test and the amount fallen during the dark test will also be less then when tested with the full light spectrum. This is our hypothesis because green light can only be absorbed through carotenoids and there are very little if any in plant leaves. So therefore, we say that barely any leaves will rise because there is no photons of light able to excite the electrons.
Methods:
The first thing done in this experiment was to take spinach leaves and cut 10 circles out of them(avoiding the veins) using straws. Once that was done, the leaflets (10 circles) were then put into a syringe. Next, 10ml of infiltration solution and 30 ml of sodium bicarbonate were mixed together in a beaker. Once those two were mixed, 8 ml of the solution was then put into the syringe with the leaflets in it. We then flipped the syringe and while placing one finger on the end so no air could escape, we then pulled on the other end of the syringe drawing out the oxygen from the leaflets. Once we pulled a little ways down, we released both ends of the syringe creating a popping noise.
Then we tapped the side of the syringe to knock off the air bubbles from the leaflets. We did this 3 times or until all of the leaflets had sunk to the bottom of the syringe. Any left floating that would not sink were discounted. Once all that was done, we placed the syringes underneath a lamp and inverted them every minute and recorded how manyn leaflets had sunk every minute until all the leaflets rose back up to the top of the syringe.
We then graphed the data taking note of when 50% of the total amount of leaflets sunk had risen. We then took the syringes and placed them in a dark box so that no light could reach them. We then inverted them every two minutes and wrote down how many leaflets had risen every two minutes until all the leaflets had risen to the top again. We did the same exact thing for the limited light spectrum experiment except we used a specific color lamp. I am not sure why we used spinach over other leaves but my theory is that it is easier to get leaflets out of the spinach while
avoiding veins. Results:
ET50 = 8.75
ET50 = 8.75
% of Floating disks during the Full Light Spectrum Experiment This graph shows the data that we collected during the full light spectrum experiment. It shows that underneath the light, it took about 8 minutes and 45 seconds for 50% of the leaflets to float.
ET50 = 20
ET50 = 20
% of Sunken Disks During the Full Light Spectrum Experiment
This data shows that during the dark part of the Full Light Spectrum experiment, that it took about 20 minutes to reach the 50% mark. We could not verify the amount of time to reach 50% of our total because we ran out of time doing the experiment.
ET50 = 17.5
ET50 = 17.5
% of Floating Disks during the Limited Light Spectrum Experiment
Our data shows that it took about 17 and a half minutes to reach the 50% mark. It reached 50% before this but right after, some of the leaves went back down so we decided on a later time because we think those leaves that went back down were not ready to float yet like we had marked them.
% of Sunken Disks During the Limited Light Spectrum
Our data shows that it took about 7 minutes and 15 seconds to reach 50%. We had such low percentage because only 6 leaves out of the total had risen after 30 minutes so we could only use 6 leaves for the dark part of the experiment. We put all of our syringes under the dark but like stated
before, only 6 were able to be recorded because only 6 had risen.
Discussion:
Our hypothesis was that the amount of leaves that rise under the light will be less than the amount that raised during the full spectrum test and the amount fallen during the dark test will also be less then when tested with the full light spectrum. Based on our results, our hypothesis was supported. The results show that under the green limited light spectrum, less photosynthesis was performed than what was performed during the full light spectrum. This is true because as stated in the introduction, chlorophyll cannot absorb green light because they naturally reflect it so therefore, photosynthesis cannot occur if the only wavelength of light shining on the plants corresponds with green light.
Bibliography
Photosynthesis. (2010). Retrieved March 31, 2013, from Photosynthesis: http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookps.html Chlorophyll and Carotenoids. (2011, January 7th). Retrieved March 31, 2013, from Chlorophyll: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chlorophyll.html Raven, P. H., Johnson, G. B., Mason, K. A., Losos, J. B., & Singer, S. R. (2011). Biology. New York: Mcgraw Hill.