Discussion

Brian Farber

The carbohydrate relationship between Bartlett pears and Mackintosh apples appears to be quite close by the methods used. Using Benedicts and Barfoed's test, we

determined that both fruits contain monosaccharide reducing sugars. We also found using Selivanoff's test that both Mackintosh apples and Bartlett pears both contain

monosaccharide ketose sugars. We concluded that both apples and pears contain a sugar that possesses a hexose-furanose ring from performing Bial's test. The Iodine

test showed that neither of these fruits contains starch. Mackintosh apples and Bartlett pears according to these tests show the same presence of carbohydrates. However

the amounts of these sugars were not tested. We did use a glucose meter to see if there was a difference in glucose levels between the fruits. We discovered that apples

possessed an average of 505.5 mg/dL of glucose while pears possessed on average 464 mg/dL of glucose. In order to make this claim statistically significant, we would

have needed to test many more replicates. In terms of sugar composition, the glucose levels existed as the only difference between the apples and the pears that we found

in our results.

The next part of the testing allowed us to see the relationship between the apple's and the pear's photosynthetic pigments. The paper chromatography test showed that

both plants are without carotene and chlorophyll b, and that they both contain chlorophyll a. The average Rf values for chlorophyll a in pears, apples, and spinach all

showed similar results, .27, .29, and .3, respectively. We believed that both plants also contain xanthophyll, but we cannot be sure due to widely ranging results between

our apple, pear, and spinach results for the pigment. In the spinach results, which functioned as our positive control, the Rf values had a mean of .95; our apples and pears

showed an average Rf value of .55. This could suggest that we made an error in measuring the apple and pear paper chromatography strips or the spinach strips. It could

also suggest that apples and pears do not contain xanthophyll at all, but rather another pigment unknown to us. These results once again show that apples and pears have

similar composition, showing that they probably have similar photosynthetic abilities.

The absorption spectra results for apples and pears showed yet another similarity. Both pear and apple trees use the same wavelengths of light during photosynthesis. Both

trees' absorption spectra showed a maximum at about 400 nm, slowly declined until 490 nm, then drastically decreased after that point. The numerical values of our apple

trees absorption spectra, however, were much lower than those of our pear trees. This discrepancy may have been caused by differing concentrations in our apple and

pear leaf solutions for the absorption spectra.

Our Hill reaction results show that apple leaves appear to perform photolysis at the same level whether absorbing white, red, blue, or no light; pear leaves followed the

same pattern. Photolysis exists as the process by which water is split when an electron is donated to chlorophyll to replace the one chlorophyll loses. In order to obtain

more meaningful results from our Hill reaction, we would have had to test pear and apples photolysis abilities under green light, where a minimum probably would have

existed, according to Dr. Urbance. This would give a more complete picture to a potential action spectrum graph we could create based on our Hill reaction results. Our

Hill reaction results, moreover, could be inaccurate due to the many problems that could have gone on during the lab. First of all, if the solutions were exposed to any

outside light the results could have been altered. Another way the results could have been incorrect was if the solutions were kept together for to long outside of the light.

The third part of our results demonstrated the enzyme activity for the Mackintosh apples and the Bartlett pears. We found, first of all, that both apples and pears contain

polyphenoloxidase (PPO). The presence of PPO causes the meat of the fruit to turn brown when exposed to air. PPO catalyzes the oxidation of catechol using a cofactor

of copper ions to produce o-benzoquinone, which in turn, leads to the color change in the fruit. We found, furthermore, that the PPO in apples and pears responded

exactly the same to the effects of changing pH. The pH graph showed similar absorbance trends for PPO under different pH conditions. Both fruits had peaks for PPO

absorbance at a pH of 7.0, suggesting that the enzyme functions optimally in neutral conditions. Heat affected PPO the same for both apples and pears; when we boiled

the fruit slurries and then added the catechol, no color change occurred, suggesting that the PPO enzyme lost its function. The heat from the boiling caused the PPO

protein to denature, or lose its 3-D shape, compromising its functionality. Phenylthiourea also completely stopped the enzyme for both apples and pears, as it absorbed all

the copper ions from the surrounding environment. Since PPO needs copper ions to function, the addition of CuSO4 to the test tube after adding the phenylthiourea

allowed for the reactivation of the enzyme. These results would suggest that PPO was present and functioned similarly in both fruits.

Using a Bradford Assay, we found that apples have a lower amount of protein than pears. Apples contained on average 0.162 µ g/ µ L + 0.207 of protein while pears

had on average 0.2465 µ g/ µ L + 0.025 of protein. After adding the standard deviation for apples to our apple protein level, however, we found that the range of protein

levels for apples and pears overlap. Therefore, though our results numerically show that the protein level difference between apples and pears exists, our results are not

significant. We cannot conclude, then, that apples and pears contain different levels of protein. Further experimentation with a higher number of replicates would be

required to come to a more valid conclusion.

There are several sources for error in this investigation. The first time the paper chromatography was done on the apples and the pears there was no result; the negative

results of our positive control proved this. Afterward, we did the experiment again this time with better results. For the photosynthesis part of the experiment some of the

leaves had started to change colors, due to the time of the year they were collected. This could have skewed our results due the loss of pigmentation in the leaves.

Our hypothesis that the apples and pears would show similar results in nearly every test that we did held. Overall, our research showed that both apples and pears have

the same carbohydrate makeup and the same photosynthetic material, and that their PPO reacted similarly to changes in pH, heat, and the addition of phenylthiourea. We

conclude that Macintosh apples and Bartlett pears are the same in what they contain, but may not necessarily be the same in the amounts that they contain it. We found,

for example, that apples and pears contain different levels of glucose and protein. For the majority of our results, the basic composition of apples and pears appeared

identical. While obviously the absorption spectra had difference numerical values for apples and pears, they usually followed the same general patterns in their respective

absorption graphs. The action spectra offered opposite results, but this could be due not to significantly different chemicals present in apples and pears, but merely the

levels that they are present. In summary, apples and pears appear to be quite closely related, though further testing needs to be done to determine the exact nature of their

relationship.

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