Assessment of the Effect of Yeast and Glucose on Gas Production

Abstract: Yeasts are single-celled fungi that can grow in the presence or absence of air. Examining a yeast cell under a microscope will give a greater understanding of the composition and nature of yeast. A hemocytometer device was used for determining the number of cells per unit volume. To measure the effect of yeast and glucose on a gas production, O2 was removed by drawing yeast into a pipet. In the first experiment the flat part between 0-3hrs is the Lag Phase, the steeply ascending part is the Log Phase, and the top around 22 hours is the Stationary Phase shows that the cells continued to grow even when the antimicrobial was introduced. For the second half of the experiment the tubes without the antimicrobial showed a little gas production followed by a stationary state, and the tube with the antimicrobial showed a continual growth in gas formation Kool-Aid kills off yeast and doesnt allow for fermentation to take place.

Introduction: Yeast is a tiny form of fungi or plant-like microorganism that exists in or on all living matter (Earthlink). Cell separation, budding, is done when the cell core migrates to the cell wall of the yeast cell. It splits up and forms a daughter cell. The daughter cell multiplies in the same way while it is still growing and tied to the mother cell. A colony develops. The multiplication process continues for as long as the conditions for multiplication are present (Earthlink). An antimicrobial is a substance that kills or inhibits the growth of microorganisms such as bacteria, or fungi (Wikipedia). In this experiment we used the Kool-Aid antimicrobial to stop the production of new yeast cells. An antimicrobial might inhibit a microorganisms ability to turn glucose into energy, or its ability to construct its cell wall. When this happens, the cell dies instead of reproducing (Smith).

For our first experiment a hemocytometer is used to determine the number of cells per unit volume (cells / mL). We counted the cell concentration of yeast at four different stages (0 hour, 3 hour, 15 hours, and 22 hours). The more yeast cells present, the less of an affect the antimicrobial has on the cells. In the second part of the experiment aerobic respiration (fermentation), we measured the formation of a gas (CO2) as an indication of how much fermentation took place. The more Kool-Aid present the less of a reaction is to take place because the antimicrobial chemicals interfere with the fermentation process to reduce the overall formation of a gas.

Materials & Methods: The sterile technique method was used to introduce the antimicrobial at different stages of yeast cells growth hour zero, hour 3, hour 15 and an hour 22. Using the bench top flame sterilization experiment, 25 mL of media and 1/3 mL of yeast was added to a 300 mL Erlenmeyer flask. For time zero, 1 standard package of cheery Kool-Aid was mixed with 75 mL H2O which was then added to the yeast mixture. Three hours into the experiment, cheery Kool-Aid was added again. 15 to 22 hours into the experiment the same procedure was repeated. A sample was then drawn from each of the four samples. To prepare the counting chamber the cover slip was placed over the counting surface prior to addition of the solution. The solution was introduced into the side of the V-shape well with the end of a pipet. Enough solution should be introduced so that the mirrored surface is just covered. For hours 15 and 22 samples were diluted 10x that of the original. In this case we multiplied our final count by the dilution factor (10fold). Removal of O2 from yeast accounts for the formation of anaerobic respiration. During respiration, the mixture of glucose and yeast were kept constant while the amount of distilled water and Kool-Aid varied. The glucose used was a 10% glucose mix. Yeast solution was prepared by mixing 7 g of Rapid Rise yeast into 150 mL of approximately 45°C water for at least 10 minutes; this allowed the yeast cells to be active and ready for respiration. The control variable 2 mL yeast, 4 mL glucose, and 7 mL distilled water. Four Kool-Aid sample sizes (1 mL, 2 mL, 3 mL and 4 mL) were observed throughout the experiment. Each sample had increments of 6 mL, 5 mL, 4 mL, and 3 mL of H2O added respectively. All of the ingredients except yeast were added at the same time once yeast is added the cells begin to grow.

To cause the cells to run out of O2, the yeast solution was drawn up through a tube by a pipet pump, the top of the tube was clamped off to kick start the formation of CO2. To assure that reactions took place at a convenient temperature, tubes were placed in a tub half filled with hot water (40°C). So that all solutions started fermentation approximately at the same time, we removed all the clamps at the same time. When it came to measuring the formation of CO2, it was important that the values on the meniscus were recorded as observed negative values stayed negative, this allowed for us to take into account were the meniscus originally was. To make things easier, we did our best to clamp off the tubes near the 0 mark on the pipet. Lastly we recorded the initial and final position of the meniscus.

Discussion: In the first experiment we predicted that the presence of an antimicrobial would kill off the formation of new cells. In Figure 1, the graph shows that the cells grew in an exponential manner. The mere presence of Kool-Aid had little, and or no effect on the production of yeast cells hence, disproving our initial hypothesis. In the second experiment we also predicted that an antimicrobial would kill off yeast and that no fermentation should take place. However, unlike that of the first experiment, Figure 2 shows that the presence of Kool-Aid killed off cells which in turn produced a CO2 gas (Dokota). In all only half of our data favored our hypothesis. Throughout the experiment we had to dilute our cells suspension to get the cell density low enough for counting. It is possible that we made an error in the case where we had to multiply our final count by the dilution factor. To assure that our experiments were valid enough, I suggest that we repeat the first experiment to see if we can come up with different results that in turn would support our initial hypothesis.