Sylvia Talbott How pH Affects Yeast’s Cellular Respiration December 19, 2006 Class G/H Introduction: In this lab how pH affects yeast’s cellular respiration is being tested. Yeast is an inactive cell in its dry state, when activated in an aqueous environment and given the necessary oxygen and food (sugar, in this lab it will be sucrose) it does a process called cellular respiration. Cellular respiration is how animal cells create energy from other molecules, but mostly from glucose (C6H12O6) when oxygen is present, when oxygen is not present fermentation occurs. The chemical equation of cellular respiration is C6H12O6+O2>ATP+H2O+CO2. ATP is the main product; water and carbon dioxide are by products. The different parts of cellular respiration occur within the cytoplasm of the cell, the cytoplasm of the mitochondria, and the cristae of the mitochondria. Within the cytoplasm of the cell a process called glycolysis occurs, when this happens a molecule of glucose is split into two pyruvic acids. The pyruvic acids then go through the process called the Kreb’s cycle, or the citric acid cycle. After the Kreb’s cycle there is a process that involves the electron transport chain. This is where most of the ATP is made. Throughout the lab the amount of cellular respiration will be measured by the production of mainly CO2 in the growing circumference of a balloon. Materials: four 250ml flasks, four balloons, four measuring boats of 5g fast acting yeast and sucrose, scale, 100ml of room temp distilled water, 100ml of 10pH buffer at room temp, 100ml of 7pH buffer at room temp, 100ml of 3pH buffer at room temp, ruler, graduated cylinder, thermometer, a length of string about 30cm, masking or duct tape, magic marker, clock or watch, pH tester strips, newspaper, paper and pencil. Procedure: Before you start your lab set up a table for the pop-up time and the measurements for the balloons afterwards…Use my graphs that appear later on as an example. The procedure is as follows… You will set up each flask of yeast, sugar, and liquid one at a time, so that the times may be staggered and it will just make life easier  Set out newspaper on your work surface so that as little as possible heat will be lost through the (usually) cold countertop. Measure out 5g of fast acting yeast, and 5g of sucrose in a boat (now would also be a good time to measure out all four boats, to make things go faster later on) on a scale. Measure out 100ml of your liquid in a graduated cylinder; water if setting up the control (be sure to measure its pH with a tester strip, its essential for this lab) or pH buffer if otherwise. Before you pour this into the flask make sure its temperature is about 30C, you can change the temperature either by putting it in a warm water bath or ice bath. Once it is at the right temperature pour the liquid into the flask and then the yeast and sugar. DO NOT LET THIS HAPPEN: This is a mess, and messes are bad. Things like this happen when friends let friends try to secure a balloon over the top of a flask by themselves! Swirl the mixture around a couple of times. Have your partner hold the flask as you secure the open end of a balloon over the top of the flask. Duct tape the edge of the balloon so that minimal carbon dioxide will be lost. Immediately take down the time for your data tables. You should also label your flasks!!! Use the marker and put a strip of tape on the flask, mark experiment number and pH value. When the yeast is activated and starts to produce energy by cellular respiration one of the by products will be carbon dioxide. We will be able to measure this by the balloons circumference; this is why we duct tape the edge of the balloon to the flask. Set up each of your flasks the same way, only changing the liquid within the flask. It will look like this once you have set up three flasks: Keep an eye on your flasks. As soon as one of them pops up record the time on your data table, also measure the circumference. To measure the circumference you will take your string and put it around the largest part of the balloon, once you have your fingers set on each end of the string where they meet align it to the ruler and record how long the segment is. If you do a graph this will be measurement zero. Measure each balloon every five minutes after it pops up for 30 minutes. Keep a table of this data. With this data we will be able to conclude which of the four pH values is best for yeast to productively respirate. Once a balloon has been measured six times after the initial pop-up you can clean up that experiment. Hold the flask and balloon facing down in a trash can and cut the neck of the balloon. Remove the tape and balloon and clean out the inside of the flask. Do this for each flask as it finishes. For balloons that do nothing (they should in this lab, but if you really killed it) you cannot measure the time it took to pop up because it never did, so on your graph it would look like a continuous bar, not a very short one. Data: Our independent variable (the one thing that we’re testing the affects of) is pH value. Our dependant variables are circumference and time. The controls are sugar type, temperature, nutrient concentration, flask size, yeast type, balloon size, balloon type, even having a balloon, and insulation material (newspaper). Pop-up Times of Balloons with Different ph Values Experiment Set up Time Pop-up Time Measurment (cm) Total Minutes Control (5 pH) 12:21 12:36 15.5 15 1 (10pH) 12:34 12:50 16 16 2 (3pH) 12:40 1:01 14 21 3 (7pH) 12:52 1:09 14.5 17 Circumference Change of the Balloons over Time Experiment Check 1 (after 5 minutes) Check 2 (10 m) Check 3 (15 m) Control (5pH) 18 cm 20cm 21.5cm 1 (10pH) 18.5 cm 19cm 20cm 2 (3pH) 16 cm 17cm 18cm 3 (7pH) 17.5 cm 20.5cm 23cm continued… Experiment Check 4 (20 m) Check 5 (25 m) Check 6 (30 m) Control (5pH) 23cm 24.5cm 26cm 1 (10pH) 21cm 21cm 23.5cm 2 (3pH) 19.5cm 21cm 21cm 3 (7pH) 24cm 25cm 26cm Explanation: The data shows that the experiment with the most success in blowing up the balloon was #3, which was 7pH, but this experiment also had a slower circumference than some experiments at the time of pop-up. It also took one of the longer times to pop-up. The control (5ph) was also very successful, it (along with #3) had the largest circumference at the end of 30 minutes. The control only too 15 minutes to pop the balloon up, that’s the shortest time of all the experiments. Experiment #2 (3pH) took the longest to pop-up the balloon, had the lowest starting circumference, and also had the lowest finishing circumference. The other experiment, #1 (10ph) was in between the other experiments. Analysis/Conclusions: The data shows us that 7ph is the best, out of each pH tested, for yeast to have productive cellular respiration. The reason this can probably be inferred that since 7ph is neutral that it is neither too basic nor acidic, but just right for cellular respiration. The experiment with a neutral pH finished with the same circumference as the experiment with 5ph. From this we can tell that neutral and just about neutral is sufficient for cellular respiration. Although, when a pH of 10 was tested, which is a small amount more basic, instead of acidic, was tested it finished far lower than those with a pH of 7 and 5. It is also shown that 3pH is the worst, it had the longest time for pop-up, and the smallest circumference at all times. 3pH is just too basic for the process to be productive. Errors: There a few ways errors could have been made in this lab. The amount of CO2 being produced throughout the experiment could have been altered if the pH value was changing inside the flask as cellular respiration occurred. Measurements could be off due to deformed balloons, there is no way in this lab to actually measure the amount of CO2 being produced inside the flask. Another error that could have potentially been made is that if the balloons were too close, when they were in fact ready to pop up they didn’t because another balloon may have been holding them down. Touching the balloons could also cause an error. Since CO2 is such a small molecule some of it could have escaped through the balloon, but we did prevent some of this with the duct tape around the edge of the balloon. The results that we got were a lot different that what I thought would happen. I thought that since when we did the cellular respiration lab with the pH indicator liquid once we started breathing out more CO2 the color changed because the pH was higher. I thought that since CO2 is apparently a higher pH then a lower pH environment would be better for cellular respiration. If something else besides O2 is present, such as CO2, then fermentation will occur, which is (obviously) not cellular respiration, and would eventually kill the yeast. Apparently I thought wrong because it was the neutral liquid that heeded the best results. The lowest pH tested actually did the worse. Poor me.  What did I learn/What do I wonder: I learned that yeast really enjoys a neutral or slightly acidic environment, not basic. I wonder if there is a way to directly test how much CO2 is being produced. Instead of using a deformed balloon that may leak, maybe there is a way to directly tell how much is being made by the yeast. Also, I wonder at what specific pH yeast does the most productive cellular respiration.