Experimentation with the Stacking of Sugars

Introduction

1. Background The purpose of doing this lab is to test the growth rate of yeast when mixed with water and sugar in various orders. When yeast is mixed with sugar it can grow in a number of different sizes depending on water temperature and amount of time. But the problem is you never know how much it is going to grow. We will be trying to figure out if you can predict the growth rate of yeast before you even mix it with sugar and water.
2. Experimental Design
   1. We are going to test if when yeast is mixed with water and sugar if the order that it is put in effects the growth rate of the yeast.
   2. The independent variable is the order yeast, water, and sugar is inserted in the test tube.
   3. The dependent variable is the growth of yeast in the time span of 8-10 minutes.
   4. The control is the water at 37 degrees Celsius.

• Hypothesis
• If the sugar is placed in with the yeast after the water, then the growth will be exponentially higher than putting sugar on top or the sugar on bottom because it would not have to mix the yeast and sugar as much.

Materials

1. Three to six test tubes (accounting for some not working)
2. One hot plate
3. One to three beakers ( depending on preference)
4. Yeast
5. Sugar
6. One thermometer
7. One ruler with metric units
8. One test tube rack

Procedure

1. Measure out 3 grams of yeast and 2 grams of sugar.
2. Measure out 25mL of water and put it in a beaker.
3. Heat the water until it is 37 degrees Celsius.
4. Put the yeast, water, and sugar into the test tube in the order that the trial needs.
5. Mark the starting position of the yeast, water, and sugar combination on each test tube
6. Wait 8-10 minutes
7. Measure the change in height

Data and Results

• While our experiments were still going on, there was one problem that came up a few times where the yeast would form a wall that the water could either not mix up or not break the wall that the yeast had just formed. Whenever the yeast was put into the test tube before the sugar and after the water, the yeast would make a somewhat concrete wall. The thing was that it only seemed to happen whenever the yeast was put in after the water and before the sugar, otherwise the yeast would go right in and not stop. Also, whenever the sugar was on top and it would start growing, it would start growing almost as soon as the water was in the tube, and you could see that it was growing instead of just looking back at it and seeing that there was more than there was a second ago.

Discussion and Analysis

• I was expecting there to be a specific order that would allow for more growth over the allotted amount of time but I did not expect it to be when the sugar was on top. I was expecting it to allow for greater growth if you put everything in after the water because then it would not have to mix as much to begin growth
• The results show that there is in fact an optimal way to layer the sugar, yeast, and water, and that it affects the overall amount of growth over time.
• The growth of the foam of the yeast is very important in this lab because it shows that there is an optimal way for the sugar to be stacked or layered with the yeast and water, which also supported the overall theme of the hypothesis, but the hypothesis itself was not supported.
• Although the experiment went well, there were several times we had to start over because we had poured too abruptly and the sugar or yeast had fallen past the test tube. Although this is a minor problem, a possible solution would be to use a funnel or something of that nature to put the things you are using for this lab into the test tube. Other than that, there were no serious flaws in the experimental design that we are aware of.

• The hypothesis was not supported by the experiment and it was found that a different method than the one suggested was optimal.

• There were a few limitations because of the equipment we were using. First of all, we may have measured out the wrong amount of sugar or yeast
• Is the "sugar on top" the optimal method for a longer period of time, maybe ten or twenty minutes?
• If you were to change the sugar to some other food source, how would the advantage of growth change?