An Analysis of The Photosynthesis Process from The Light Dependent and Light Independent Reactions

Introduction

We as heterotrophs rely on photosynthetic organisms for nearly all the organic plant matter that we consume for energy. Photosynthesis is one of the oldest and one of the most fundamental processes of life. ("BIO 1510 Laboratory Manual," 2015, 131) We study the process of photosynthesis because of just how important it is to our life. Theoretically, scientists that are able to understand the concepts of what plants need to produce what we need from them are then better poised to make more efficient plants in the laboratory. So what do these plants need? Well the photosynthetic process is composed of two chemical reactions. The light reaction and the Calvin cycle. The first set of reactions require light to proceed, and are sometimes referred to as the light dependent reactions, in it, color pigments on the plants leaves grab electrons and pass them along to a coenzyme known as NADP+, which is similar to NAD+ in aerobic respiration. The final process yields energy in the form of NADPH as well as ATP through the process of photophosphorylation. The second set of reactions, sometimes referred to as the light independent reactions, proceed as long as ATP and NADPH are available. The reaction grabs atmospheric CO2 and uses the energy molecules to convert it to an organic molecule for storage, commonly glucose because of its easy convertibility to more complex molecules. ("BIO 1510 Laboratory Manual," 2015, 131) In this lab we attempted to analyze aspects of the photosynthetic process from both the light dependent and light independent reactions.

The first experiment investigated the pigments involved with the process of photosynthesis. Using Thin Layer Chromatography, we analyzed four pigments found in organic matter, Chlorophyll A which is the primary pigment required for photosynthesis to occur, there is also the accessory pigments found in most plants, Chlorophyll B, Carotenes, and Xanothophylls. Their presence helps broaden the spectrum of light the plant can absorb, and the accessories are also the reason that leaves turn color in the fall. ("BIO 1510 Laboratory Manual," 2015, 133) As the temperatures lower the Chlorophyll A pigments which are blue-green die off leaving the Carotenoids which are yellow-brown. We expected our TLC strip to look similar to the one found on the back of the Bio lab book’s cover page.

Experiment two was designed to see the amount of oxygen the photosynthetic process releases when it is absorbing different lengths of visible light as well as the availability of CO2. From the background information we gathered from experiment one, we knew that blue-green was the actual color of Chlorophyll A, which is nearly 75% of all the pigments on the plant. ("BIO 1510 Laboratory Manual," 2015, 133) We made the hypothesis that blue light was going to be most effective, and then the red light behind that. When compared to white light, we said that the blue light would still be more effective because the only thing entering the blue light tube is the light that it can most efficiently process. This is why regular white light makes a good control. The other aspect of this experiment, CO2 availability can also be tested with the same exact procedure, just a different amount of the inhibitor that absorbs CO2 we predicted that the plant in this tube would produce less oxygen.

In experiment three we attempted to learn about the light reactions versus the light reactions qualitatively. By absorbing color difference when leaving the reactions to react in their respective environments, we hypothesized that we could see the reactions proceeding by the color change. We expected only the tube that was left in the light to change color. As the other three did not have the correct prerequisites for a light reaction. With one of the tubes being in the dark, the other having denatured chloroplasts, and the final one having no DCPIP. In order for the light reaction to proceed, it needs chloroplasts, access to light, and NADP+ or in this case the artificial DCPIP. ("BIO 1510 Laboratory Manual," 2015, 131)

The procedures for these three experiments can be found in the lab manual on pages 135 and 138 through 140. For experiment one note that the TLC sheet was 15cm long. For experiment two instead of every group or table doing every possible color and CO2 combination, we each only did one tube, analyzed it for an hour, and compared all of our results at the end.

Our chromatography strip is similar to the one on the back of the lab manual, however our xanthophyll is much closer to the origin, actually being the closest one. We also did not notice the presence of any degraded chlorophylls known as phaeophytins.

Discussion

This set of experiments was overall successful in gaining insight into the basics of the photosynthetic process. In experiment one we analyzed the individual pigments that make photosynthesis possible, while in experiment two we tested under which lighting circumstances those pigments are most effective. Finally experiment three was an attempt at gaining a qualitative look into the process of the light dependent reaction of photosynthesis.

Although we followed the procedure errors were made in the collection of our data, there were four large errors to make note of here, first the TLC sheet, when placed into the tube, did curve slightly into the solution at the bottom, this led to our solvent front being somewhat sideways, because of this it is important to note that the solvent front that we used for our measurements is the point in which the whole sheet was still wet and not the farthest point. The second error came in experiment two with the dataset White light with 0% NaHCO3 while the blue light was the hypothesized and expected result for the efficient production of oxygen, it ended up being that the tube aforementioned had a higher rate of photosynthesis. We have deduced that this was either the result of a measuring error or it came about from the fact that that tube had deionized water in it which has a higher oxygen content than normal tap water. Another error in experiment two resulted because the group that had the green tube did not take the initial weight of their biomass and as a result we were not able to calculate the photosynthetic rate of the green tube, this is shown on graph 1 in the results section. The final error has to do with experiment three, it is a result of the procedure telling us to use too much DCPIP in our trials. The twenty minutes of time was not enough for the chloroplasts to convert all the DCPIP and as a result no color change was observed in any of the tubes so our hypotheses could not be proven, one group repeated the trial with 1mL of DCPIP and got the results that our hypothesis was expecting, confirming that this was the error.

We can use these results from the lab to answer a real world question, one about a pesky weed that can ruin your camping trip and leave you itching for relief. Talking about the world population of poison ivy, which has a slightly different photosynthetic process then most normal plants. Poison ivy actually benefits from an environment more conducive to higher CO2. As a result the effects of global warming, releasing more carbon dioxide into the atmosphere, is likely to increase the global population of poison ivy, as well as the average size of the plants. So in the future, be on the lookout for more aggressive populations of poison ivy on your nature hikes.