Yeast Beasts in Action Lab Investigation

Today we had a lab that measured the amount of pressure conducted when a yeast and water mixture is poured into an acid mixture, neutral mixture, and a basic mixture. Our hypothesis was the the yeast activity in the acidic mixture will be the greatest because the more acidic something is the greater the reaction. Our problem was how does yeast activity differ in acidic, neutral, and basic mixtures. Some of the materials that we used were a computer, Vernier computer interface, gas pressure sensor, 1 hole stopper assembly, 10 mL graduated cylinder, 3% hydrogen peroxide, yeast suspension, 3 test tubes, test tube rack, dropper, acidic mixture (diet soft drink), neutral mixture (skim milk), and basic mixture (stomach antacid).

First, we had to pour 3 mL of hydrogen peroxide into each test tube and labeled them with a sticky note, A for acid, N for neutral, and B for base. Second, we had to pour 3 mL of each mixture into its designated test tube. Next, we had to make the yeast solution which was 50mL of water and 1/2 tsp of yeast. We poured 1 dropper full into the acid solution, placed the gas pressure sensor into the test tube, and collected the data, we repeated these steps with every single mixture that we did.

Mixture	mL of Hydrogen Peroxide	mL of Mixture
A (acid)	3mL	3mL
N (neutral)	3mL	3mL
B (base)	3mL	3mL

The objectives for this lab were to use a computer and a Gas Pressure Sensor to measure pressure, measure and compare yeast activity in acid, neutral, and basic mixtures, and make a conclusion about yeast activity.

Our hypothesis was not correct, we said that the more acid something is the greater the reaction will so it will have the greatest pressure. This did not happen. The basic mixture had the highest amount of pressure which was 124.04 kPa.

Mixture	Highest Pressure kPa
Acid (diet soft drink)	118. 62 kPa
Neutral (skim milk)	111. 97 kPa
Basic (stomach antacid)	124. 04 kPa

1. In which mixture was the yeast activity greatest? Explain.

The activity was greatest in the basic mixture. I do not know why it was the highest in the basic mixture because I thought that the acidic mixture would be the one which had the largest amount of pressure. Because the mixture contains hydroxide ions in it while the acid had hydrogen atoms. Hydrogen is the lightest element known to man and that lack of mass might have something to do with the amount of pressure. The hydrogen peroxide is made of hydrogen and oxygen atom stuck together and it can create an acid when the oxygen atom is released. I think that the hydrogen peroxide and hydrogen are pretty much the same, except for that extra oxygen atom and that's what makes the difference in the gas pressure.

2. In which mixture was the yeast activity least? Explain.

The neutral mixture had the lowest amount of pressure because neutral is right in the middle and it is neither basic or acidic.

3. What can you conclude from the results of your experiment?

I can conclude that bases cause the most pressure and gas to be produced and neutral mixtures produce the least gas and pressure.