The effect of zinc chloride on the formation of food vacuoles in <i>Tetrahymena thermophila</i>

Abstract

Heavy metals, such as zinc, are essential nutrients required by organisms for survival, but can be toxic at high concentrations. In this study, we tested the effects of increasing concentrations of zinc chloride on the formation of food vacuoles in Tetrahymena thermophila. We were also interested in seeing if increasing incubation times in zinc chloride affected food vacuole formation. These were the basis for our three hypotheses, which tested for the effect of zinc concentration, time, and zinc and time together, on the formation of food vacuoles. Our experiment involved introducing three different concentrations of zinc chloride (0 mg L^-1, 50 mg L^-1, and 120 mg L^-1) to the nutrient medium of T. thermophila. We incubated for three different time intervals (20 minutes, 2 hours, and 26 hours) before adding India ink to stain the food vacuoles and fixing the T. thermophila. After the cells were fixed, we counted the number of black food vacuoles (those that have engulfed the India ink) for 10 cells in each treatment for 3 replicates each, resulting in nine averages for each permutation of [ZnCl₂] and time treatment. Finally, we conducted a two-way ANOVA analysis and found that our p-values for our [ZnCl₂], time, and both factors considered together to be 2.5 x 10^-3, 2.6 x 10^-6, and 0.31, respectively. We were able to reject our first two null hypotheses, providing support for our alternate hypotheses. Our results may be due to zinc’s inhibitory effects on the formation of cilia as well as the physiological changes that starved T. thermophila undergo. However, the p-value was greater than 0.05 when both factors were considered together, so we failed to reject our final null hypothesis. This is most likely due to our low zinc concentration not being trace enough compared to successful experiments in the past (Nilsson 2003).