THE YEAST OF OUR WORRIES
OVERALL PROBLEM
1. Do yeast demonstrate any of the characteristics of life?
EXPERIMENTAL PROBLEM:
1. Do yeast use energy when food (sugar) is available?
2. What evidences may be observed to indicate that cellular respiration occurs?
MATERIALS PER GROUP:
4
Sugar
Warm water
7 test tubes
Test tube rack
Yeast
Bromothymol Blue
6 balloons
4
BACKGROUND INFORMATION
Living things need food. Food provides energy and building material to create more living mass. Living things must be able to break down food in order to obtain energy to carry out their activities. When food is broken down in a process called cell respiration, carbon dioxide is made and released. The process of cell respiration occurs in every cell. Carbon dioxide is a gas and thus will cause bubbles in solution. These gas bubbles will escape from the solution into the atmosphere if not captured somehow. A pH indicator known as Bromothymol Blue, tests for the presence of carbon dioxide by turning color. In the presence of carbon dioxide Bromothymol Blue will go from blue to green to yellow.
Yeast are tiny single-celled (unicellular) fungi. The organisms in the Kingdom Fungi are not capable of making their own food. Fungi, like any other organism, need food for energy. They rely on sugar found in their environment to provide them with this energy so that they can grow and reproduce.
Yeast, like bacteria grow in or on their food source. They produce and release digestive proteins (enzymes) into their environment where the sugar molecules are found. Sugar molecules then break down into smaller molecules that can be absorbed by the yeast and used for food (energy).
Yeast are facultative anaerobes, which means that they can respire or ferment depending upon environmental conditions. In the presence of oxygen, respiration takes place (aerobic respiration). Without oxygen present, fermentation occurs (anaerobic respiration). Both processes require sugar to produce cellular energy and both produce carbon dioxide as a waste product.
PROCEDURE:
PART A:
1. Obtain six test tubes and label each test tube with your groups name as well as the following:
a. Test tube 1
b. Test tube 2
c. Test tube 3
d. Test tube 4
e. Test tube 5
f. Test tube 6
2. Add to each of six test tubes 15 ml of warm water (4/5 full).
3. Slowly add 1.25 grams of yeast to test tubes 1-4, mixing the yeast in thoroughly before adding more. Mix by putting your thumb over the top of the test tube and shaking.
4. Add 1.25 grams of sugar to test tube 1, 2, 5 and test tube 6. Do not add sugar to test tube 3 or 4.
5. Cover the opening of each of the six test tubes with a balloon to catch any gas that is formed. Using the balloon to seal the end of the tests tube, hold a finger over the end of each test tube, and shake it vigorously to thoroughly mix the contents.
6. Make sure none of the materials remains clumped at the bottom.
7. Write time of initial setup ______
8. Record initial observations in data table below.
9. Record observations at 20- 30 minutes after completing setup record your observations of the balloon and contents in the table below:
10. After 24 hours record your observations of the balloon and the contents in table below:
PART B:
1. Wait until at least one balloon is inflated
2. Fill a 7th test tube with Bromothymol Blue
3. Carefully remove the balloon that has inflated the most making sure not to release contents of balloon.
4. Slip balloon over mouth of test tube with Bromothymol Blue.
5. Squeeze contents out of balloon into test tube.
6. Gently mix test tube and observe and record any color changes.
RESULTS:
THE EFFECT OF SUGAR ON YEASTTest tube # / FROTH/BUBBLES / BALLOON INFLATION / BROMOTHYMOL BLUE COLOR CHANGE
1 / 2 / 3 / 4 / 5 / 6 / 1 / 2 / 3 / 4 / 5 / 6 / 7
INITIAL TIME / X
20-30 MINUTES
24 HOURS
ANALYSIS-CONTENT
1. If you knew nothing about yeast except for the results of this experiment, could you call yeast a living thing? Explain your answer using evidence from this investigation.
2. What characteristic(s) of living things were demonstrated in this investigation? Explain why.
3. Which test tubes did cell respiration take place? Explain
4. What substance served as food? What is the evidence for your answers?
5. Was the food broken down and energy released? If so, what broke down the food? What is the evidence for your answer?
6. What does the inflated balloon tell you?
7. What does the Bromothymol Blue changing colors from blue to green or yellow tell you?
8. What does the presence of carbon dioxide indicate?
9. What is the name of the process that involves breaking down food to extract energy for a living thing to use?
10. What are the reactants in the observed reaction given in # 9?
11. What are the products in the observed reaction in #9?
12. Why do organisms need food?
13. How did you know if carbon dioxide was being produced?
14. If bubbles appeared in test tube 3 and 4 or balloon inflated, how did it compare to test tubes 1& 2 and how can you explain it?
PROCESS OF SCIENCE BACKGROUND:
1. The control is the standard against which the researcher compares the results from each treatment group (level) in the experiment. It is the same as the treatment group(s) except it lacks the independent variable.
2. The independent variable is the variable that is intentionally changed in the experiment by the researcher. The levels of the independent variable are the different values of the independent variable, such as using water at 10°, 20°, 30°, 40°, and 50° C. The levels of the independent variable can also be thought of as the experimental groups that are set up.
3. The dependent variable is the variable that responds to the changes in the independent variable. It is what is being measured.
4. Constants (control variables) are the things that are kept the same in both the control group and experimental group. As many outside factors as possible should be kept constant in an experiment so that the researcher can be sure that any changes that occur do so because of the independent variable.
ANALYSIS-PROCESS OF SCIENCE
1. Which test tube(s) in experiment 1 would be considered a control? Explain your answer.
2. In experiment 1, what is the independent variable?
3. In experiment 1, what is the dependent variable?
4. In experiment 1, list three constants or control variables.
5. Why is it better to have two test tubes with yeast, sugar, and water, two test tubes with just yeast and water, and two test tubes with sugar and water instead of only one test tube with each type of mixture?
6. Why did testing the gas in the balloon with Bromothymol Blue make this a better experiment?
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