The Minimal Effects of Growth Methods on Enzymes,

Carbohydrates, and Photosythesis of Lettuce



Luke Zoet, Jessica Brown, Heather Rothe,

Steve Shaheen, and Yvette Gross



Controversy between organic and non-organic foods has been on the rise. Several people believe that pesticides and fertilizers, used to enhance the crops, are harmful to the nutrients in the crops. We tested three samples of lettuce, including two non-organic lettuces, one rinsed, one un-rinsed, and an organic lettuce. Our labs included: tests for carbohydrates: Benedicts, Barefoeds, Selivanoffs, Bials, and the Iodine test; for photosynthesis: Pigment identification, Action Spectrum and Absorbance Spectrum; and Enzymes: Environmental effects on enzyme activity including the presence of PPO, effects of heat, inhibitors and pH (Maleszewski, Wilterding, Sayed, Luckie 2002).
According to the carbohydrate, photosynthesis and enzymes labs that were performed on the three samples of lettuce, there was not a significant difference established between the samples. The sugars, photosynthesis, pigments, absorptions, and enzymes were tested in each type of lettuce. The sugars present in each sample were polysaccharides, and aldoses, each containing a six-carbon chain, galactose, and were free of starch.
Each type of lettuce was shown to have a large amount of chlorophyll, although the chlorophyll in the organic lettuce was more apparent. The organic lettuce was found to have a slightly greater presence of enzymes then the non-organic rinsed and un-rinsed samples. This was because organic lettuce did not have the slightest interference of pesticides, water, or other altering factors. This difference is minute and not significant enough to conclude a healthier type of lettuce between organic, non-organic rinsed, and non-organic un-rinsed lettuce.


Figure 10: This figure is of the absorbance spectrum of lettuce for the photosynthesis lab (Lab 2) Trial 1. The absorbance of the all three types of lettuce is on this graph in 15nm intervals from 400 nm to 700 nm wavelength of light. On the graph blue is for the Organic lettuce, pink is for the non-organic rinsed lettuce and yellow is for the non-organic Un-Rinsed lettuce. On this graph we are concentrating on the green light section, which is around 540 nm.


Is organic lettuce all that it is cracked up to be? In our opinion, the growth methods of conventionally processed lettuce, washed or not, does not significantly change the carbohydrates, enzymes or photosynthesis compared to organically grown lettuce. We do not believe that organic lettuce has anything more to offer than commercial lettuce and is not worth the extra expense. This hypothesis is supported by the results of testing the presence of sugars, photosynthesis and enzymes.
In the carbohydrate lab, we were able to conclude that all three-lettuce types showed little to no difference to one another. The Benedicts, Barfoeds, Selivanoffs, Bials, and Iodine tests were the tests preformed to show these results. In the Benedicts test, the organically grown lettuce sample resulted in an aldehyde, while the other two specimen exposed to pesticides, tested positive for ketoses. We know that from reading Campbell's Sixth Edition, that lettuce contains cellulose, and cellulose is glucose chain, which are in fact an Aldose. We also knew that glucose is linked together to make polysaccharide cellulose. The Barfoeds test showed that monosaccharides were present in all the lettuce types. This was because of the red precipitate that formed. The Iodine test was used to test for the presence of starch within the three lettuce types. After conducting this test, we found that none of the lettuce contained starch. After performing the Selivanoffs test, we concluded that the lettuce samples were aldoses because the color changed in less than one minute. The Bials test indicated that the lettuce contained pentose and furanose, as the solution turned olive/green after being heated (Table 1). Although the organic lettuce showed the darkest color, the non-organic and non-organic rinsed lettuce samples were very close to the same color as the organic lettuce.
Through the photosynthesis lab, we were able to see a small change in the amount of pigment from the organic lettuce and other lettuce samples. This was expected because organic lettuce is all-natural. It does not have pesticides on it; therefore, organic lettuce has nothing inhibiting its photosynthetic process. Chlorophyll A and B were obviously the darkest colors for the organic lettuce paper chromatography, which was used to find the pigments. This is because chlorophyll is found in any green vegetable, and organic lettuce is of course the most natural in color.
As for the absorbance, the organic lettuce had the highest absorbance. It had the highest percent of absorbance at 535 nm, as this value is very close to 540nm, which is the green color on the spectrum of colors (McMurry, 2001). The pesticides used on the commercial lettuce clog the pores of the lettuce, and therefore inhibits photosynthesis (Ehler, 2002). This does not allow the non-organic to absorb as much light. This however, does not have a drastic effect and therefore does not yield significant evidence of the effectiveness of pesticides.
The action spectrum showed the same results for all three types of lettuce. Each type of lettuce absorbed white light the best because white light contains every visible color. The action spectrum plots the light wave against the photosynthetic rate. By looking at this type of graph, one can tell which wavelength photosynthesis works the best at.
When testing the enzymes, we observed that the organically grown and rinsed lettuce have the same enzymes. The non-organic lettuce had a lower enzyme count because the pesticides are enzyme inhibitors. This is a very slight change and pesticides do not have enough of an effect to state that organically grown lettuce is superior.
PPO, polyphenoloxidase, is an enzyme capable of catalyzing the oxidation of certain organic molecules. Catechol is a substrate that will result in a color change. After testing for the presence of PPO by adding catechol to each type of lettuce sample, all the tests came back positive, meaning the PPO was present.
When testing for heat and inhibitors, one tube was the control, another was submerged in boiling water, and the last tube had phenylthiourea added to it. The first tube turned green. The last tube turned partially white because phenylthiourea inhibited those enzymes in that specific tube. The effect of pH told of the optimal pH value for enzymes to react the best. This is a value of 6.5. All three lettuce types had the same value.
Enzyme regulation was performed to tell of the Km values for the lettuce types. This is used to help tell of the affinity between an enzyme and it's substrate. The Km value is a constant, in which during a series of reactions, the concentration of enzymes is held constant, while the concentration of substrate is varied (Maleszewski, Wilterding, Sayed, Luckie, 2002). The Km value ultimately tells the concentration of substrate that will use half of the enzyme (Figures 15-20)(Tables 20 and 21). In figures 15-20, the slopes are either constant or at zero and do not level off at any point. The leveling off point is used to tell when the enzyme is totally saturated, and is also known as the Vmax value. Vmax is the value that the enzyme concentration determines. This value is determined at high substrate concentrations when all enzyme molecules are involved in complex formation (Maleszewski, Wilterding, Sayed, Luckie, 2002).
Biology is around us everyday. It is even in the supermarket. For years now, there has been an ongoing debate about the so-called benefits of organic vegetables. In this debate, it is argued that organic lettuce has far more nutrients and is better for you than traditionally grown lettuce. But in reality, people are paying higher prices for vegetables and fruits that are not significantly different. As we have stated previously, we have shown that there are very slight differences between the non-organic and standard lettuces. There are no differences in the carbohydrates and a very small difference in the photosynthesis and enzymes (proteins/nutrients). These differences are not significantly large enough to make the statement that organic food is better for you. A study relating to this subject was preformed at Macdonald Collage. Protein enzymes were studied in vegetables that were organically fertilized vs. those that were chemically fertilized. This was a six-year experiment that resulted in no difference between the different fertilized vegetables.
Organic farmland only takes up less than one percent of the total farmland and supply less than two percent of the nations food in America, but nearly forty percent of U.S. consumers buy something labeled as organic. They spend eleven million dollars a year on this produce. Cropland used for organic growing increased from 400 acres to over 800,000 acres and the number of U.S. growers that were certified as organic rose from 350,000 to 500,000 between 1992 and 1997. As of October 21 of this year, organic food must meet criteria to be labeled as "organic." This is set by the United States Department of Agriculture. These products must be produced without hormones, antibiotics, pesticides, synthetic fertilizers or genetic modification. Under the new guide lines, meat and dairy labeled as organic must come from creatures that are raised on organic grains or grasses, given access to the outdoors and spared treatment with growth hormones and antibiotics. Lettuce is the top organic crop, making up roughly about twelve percent of the acreage devoted to vegetables. Although the "organic trend" seems to be on the rise, conventionally grown foods are still very safe. Produce should be washed, but it should not be made into a large issue. Fruits and vegetables are the best fuel you can put into your body, regardless is they are organic or conventional (Springen and Underwood, 2002).
One weakness in our experimental design is the lack of tests. We have only chosen to test some aspects of the lettuce, making our hypothesis a guess that cannot be truly answered just by the test we administer. Our test could have also been improved by testing amounts instead of presence, therefore being able to acknowledge particular differences instead of general differences. This has affected our results by the fact that although there may have been a difference, we cannot say that there was because our results state otherwise. Another source of error is human error. Concentration can be mis-measured and most of the results are subject to opinion, such as determining color. One other error was that Benedicts test said that there were free or potentially free aldehydes in the organic lettuce, while Selivaoffs said that the organic contained ketose. This could be because the pesticides affected the test and caused an error in the results. In all experiments, there is the risk and the chance of human error. This can affect the results by giving incorrect data, and therefore a wrong and confusing result. Another source of error might be between the non-organic and non-organic rinsed lettuce. They may be similar to each other because even the un-washed lettuce was probably rinsed to some extent in the grocery store. One unforeseen problem was the time in which it took to complete all the tests in one time session, therefore creating problems with the whole group effort.