2644 - CSUN ScholarWorks - California State University, Northridge

2740
Journal of Student Research Abstracts · 47
THE EFFECTS OF CITRUS OIL ON THE REPRODUCTION OF DROSOPHILA
MELANOGASTER.
Jason Poon and Steve DeGusta (teacher). John F. Kennedy High School, 6715 Gloria Drive, Sacramento,
CA 95831.
The main objective of this investigation was to determine whether or not citrus oil, specifically orange citrus
oil, was toxic to the reproduction of fruit flies Drosophila melanogaster. Therefore, a control group, four culture
tubes filled with 10 ml of instant .drosophila medium, and an experimental group, four other culture tubes
filled with 10 ml of instant drosophila medium as well as 2.5 g of finely diced orange peels, were used. The
orange peels provided the tubes with the citrus oils needed to combine with the medium. Three female and three
male VS Drosophila were added to each tube. After three weeks a count of the offspring was made to see if the
citrus oils killed off some of the offspring, and the count resulted with 444 flies for the control group and 85
flies for the experimental group. There was a highly significant difference between the control at)d the experimental
(X 2 = 243.6, p < 0.001), thus proving that orange citrus oil was toxic to the reproduction of fruit flies.
2741
THE EFFECT OF BREAD MOLD'S GROWTH ON THE pH VALUE OF THE
MEDIUM
Eric Yeung and Steve DeGusta (teacher), John F. Kennedy High School, 6715 Gloria Drive, Sacramento,
CA 95831.
The purpose of this experiment is to test if bread mold's (Rhizopus nigricans) growth will cause an increase
in the pH value of the medium that it grows on. I mixed Brom Thymol Blue indicator and vinegar with nutrient
agar and used it as the medium for the bread mold to grow on. The vinegar gave the agar an initial color
of yellow, indicating a pH value of about 6. Then I transferred bread mold aseptically to the agar for the experimental
group of 20 petri dishes, while nothing was transferred to the 20 petri dishes of the control group. The
petri dishes were observed for the next four days and the color of the agar in each petri dish was recorded. The
color of agar in all of the control plates remained yellow indicating a pH value of about 6, while the color of
agar in all of the experimental plates changed to blue indicating a pH value of about 7. According to the results
of this investigation, I conclude that the growth of bread mold causes an increase in the pH value of the medium
that it grows on.
2742
EFFECTS OF CONCENTRATION ON THE pH OF A PHOSPHATE BUFFER.
G.J. Fornero, J.W. Lee, P. Porazik and B. Van Duzee. Saugus High School, 27900 West Centurion Way,
Saugus, CA 91350.
A phosphate buffer with neutral pH is one of the most commonly used reagents in biological studies. Proper
preparation of such buffer with defined pH is essential for accurate and reproducible measurement for biological
acitivities. To understand the concept of acid-base equilibration and how changes in concentration affects
the pH of a buffer, we measured the pH of a series of increasingly diluted potassium phosphate buffer and compared
the observed pH values to the calculated values. We prepared a 400 mM pH 6.8 solution and then diluted
to 300, 200, 100, 50, 25 and 10 mM, respectively, with water. It was found that the pH of these serially diluted
phosphate buffers are pH 6.80, 6.83, 6.89, 6.94, 7.02 and 6.99, respectively. In contrast, a calculation based
on dilution alone predicts the pH to be 6.92, 7.10, 7.40, 7.70, 8.00, and 8.4 respectively. The slower than
expected increase in the measured pH indicates that dilution of phosphate causes increases in proton concentration
as the result of a shift in the acid-base equilibration towards the dissociation and release proton ions.