pH and Yeast. uh oh

Abstract: 

In this experiment, my partner, Chris Jung, and I explored the effects that pH had on the cell respiration of yeast. We altered the pH of 3 different yeast/water/glucose solutions, while keeping a control solution. Thus, we ended up with one acidic solution with a pH of 1-2, our control at a pH of 7, and two basic solutions with a pH of 8 and 9. We measured the rate of cell respiration by the amount of CO₂ created. The results showed that the optimum pH for the cellular respiration of yeast is more acidic than basic, and is closer to 7 than 1 or 2.

Background:

            Cellular Respiration is a process that is essential to all life. Through cell respiration, ATP is captured from the chemical energy released after digesting foods like carbohydrates, fats, and proteins.

The process of Cellular Respiration uses the fuel of glucose/fructose/galactose and oxygen to create carbon dioxide, water, and 36-38 ATP, which is then used to normal bodily functions. This can be seen in the chemical formula, C6H12O6 +6O2 → 6CO2 + 6H2O + 36-38 ATP.

            There are three parts to Cellular Respiration: Glycolysis, Krebs cycle, and oxidative phosphorylation. In glycolysis, which occurs in the cytosol of the cell, the 6 carbon (glucose/fructose/galactose) is broken down, through the investment of 2 ATP, into 2 three carbon chains a.k.a pyruvate. The pyruvate molecules are then oxidized and both lose one Carbon in the form of Carbon Dioxide. These 2 two carbon chains, acetyl coA, are then taken into the matrix of the mitochondria to participate in the krebs cycle. Here, NADH and FADH₂ are formed and carry electrons off to the Christae and Electron Transport Chain. In this last phase of Cellular respiration, the electrons are transferred through carriers from one protein to another, with oxygen being the final acceptor. Each time, hydrogen is attracted and led out the membrane. Eventually, a higher concentration of Hydrogen is formed on the outside compared the inside. This group of protons goes through chemiosmosis, and is pumped through the membrane by the ATP synthase. Once pumped through, the hydrogen join oxygen to create water. The energy released during this process is used to form ATP.

            However, we know that because yeast is unable to go through aerobic respiration, it goes through fermentation a form of anaerobic respiration. In fermentation,

C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide),

Glucose is changed into energy, with ethanol and carbon dioxide as the waste products. In yeast, there the enzyme zymase is responsible for breaking glucose anaerobically to ethanol and CO2.

Hypothesis: 

Because yeast is able to go through cellular respiration in solutions with plain water, the farther away the pH in a yeast solution is from 7 the slower the rate of cellular respiration will be. Out of all our experiments, our control will have the best results.

Materials:

·         4 test tubes

·         Salt

·         Glucose

·         Yeast

·         Warm water

·         4 test tube stoppers with holes and pipes in them

·         4 syringes that connect to the test tubes pipes

·         Timer

·         Test tube rack

·         HCL

·         NaOH

Procedure:

1.      Before you start, collect the 3 solutions that your teacher so kindly created for you, because you were too slow. These solutions should then be labeled with their appropriate pH levels: 1-2, 8, and 9. These solutions were created by a mixture of water and HCL or NaOH.

2.      Collect 4 test tubes and label them, 1, 2, 3, and 4.

3.      Fill each test tube with 1 gram of yeast and 1 gram of salt each.

4.      Fill test tube # 1 with 35 mL of warm water

5.      Fill test tube #2, with 35 ml of the solution with a pH of 1-2, test tube #3 with 35mL of the solution with a pH of 8, and test tube 4 with 35 mL of the solution with a pH of 9.

6.      Connect each test tube with a stopper, tube, and a syringe.

7.      Make sure each syringe is starting around 2.0 ml

8.      Wait 5 minutes for the process of cell respiration/fermentation to begin.

9.      After the 5 minutes, every minute measure the amount of CO2 produced.

a.       To measure how much CO2 is being released, push down the syringe, then wait for it to rise, and read the new number.

10.  Do this for 10 minutes, or as long as you can to get some clear results.

Results:

Time (min) \ pH	7 (control)	1-2	8	9
1	2.3	2.4	2.0	2.1
2	2.4	2.2	2.2	2.4
3	2.4	2.0	2.4	2.4
4	2.5	1.9	2.5	2.4
5	2.6	1.2	2.6	2.4
6	2.8	0	2.6	2.4
7	2.9	0	2.8	2.6

All four lines should have started 2.0 and should have continued to 7 minutes. There were some technical difficulties.
The Title of this chart is effects of pH on production of CO2

Conclusion:

            In this experiment, the pH of the environment of the yeast was changed. The results matched my hypothesis. Because of fact that yeast can release carbon dioxide normally with simple tap water already, it was hypothesized that the amount of co2 produced would be greatest the closer to the pH of 7, like our control.

            The results show that our control, the yeast solution made with only water (pH of 7), had the greatest amount of carbon dioxide emission. Solution 3 and 4 had the next greatest amounts of CO2 emission, in that order. This makes sense seeing as how solution 3 (pH of 8), which is closer to solution 1 in terms of pH instead of solution 4, had a greater emission than solution 4. Solution 2, with a pH of 1, had the lowest amount of emission; in fact, there was absorption of CO2 apparently. This, however, may have been a result of a leak. Still, if it was intentional, it makes sense, for the enzymes in the yeast, zymase, was denatured, and forced into a habitat  far from its optimal level.

            After some research, I found that the optimal pH level for zymase is 6 (5-7), proving the results of my experiment. Though there were many small errors in my lab report, like not capping the test tubes immediately, the results were still able to be conclusive, and accurate.

            For future experiments, I would hope to use more solutions, one for the pH levels of 1-14. I would also like to take measurements every 10 minutes, for I had run out of time during this experiment.