IS YEAST ALIVE? Humans use yeast every day. We use yeast at home, in research laboratories and in industry. What is yeast, and what are some of the common uses of yeast? Yeast has the consistency similar to little brown grains of rice and can be purchased at your local grocery store. Your essential question for this lab is: Is Yeast Alive? To answer this question we will carry out an indirect test for metabolism. In other words, we will be indirectly testing whether yeast can use energy in the same way other organisms do (remember back to your characteristics of life lecture). When Humans and other organisms use energy, they break down high-­‐‑energy molecules like sugar to get energy they need and give off a gas called carbon dioxide (CO2) as a by-­‐‑product of that reaction. We will test whether yeast can metabolize sugar and produce a gas, which we will presume is CO2. Specifically, we will test whether yeast produces gas when it has sugar available as a food source vs. when no sugar is available. Pre-­‐‑Lab Questions: 1. What is yeast? Explain to the best of your knowledge what this is. 2. What is metabolism? (use your notes or book) 3. How do humans produce CO2? 4. Read the instructions thoroughly and answer the following questions a. What is the independent variable and how do you know? b. What is the dependent variable and how do you know? c. What is a constant variable; provide an example. d. Is there a control group, if so what is it? e. How much yeast will be added in each test tube? __________ f. How many test tubes will have sugar put in them?_________ 5. What type of data are you going to collect? (hint: there are two types) ___________________________________ 6. Write a hypothesis for this lab. Materials and Methods: -­‐‑ 4 test tubes & 1 test tube rack -­‐‑ Four Balloons -­‐‑ 1 g (x 2)of Sugar (approx. ½ tsp) -­‐‑ 250 ml of warm water -­‐‑ 2g (x 4) of Yeast (approx. 1 tsp) -­‐‑ Stop watch
1. Set up 4 test tubes in the rack and label them 1-­‐‑4. a. Test tubes 1 & 2 will have both yeast and water. b. Test Tubes 3 & 4 will have yeast, sugar, and water. 2. Add ¼ of a tbsp of sugar test tubes 3 & 4 3. Add ½ tbsp of yeast to test tubes 1-­‐‑4 4. Add 15 ml of warm water to each test tube, hold a finger over the end of each test tube and shake it vigorously to thoroughly mix the contents of each test tube 5. Quickly cover each end of the test tube with a balloon; being carful not to rip the lip of the balloon. 6. Observe every 5 minutes and record any changes in the test tubes and record these and all other observation in the table below. Results: 0 minutes 5 minutes 10 minutes 15 minutes 20 minutes 25 minutes Tube 1 Tube 2 Tube 3 Tube 4 IS YEAST ALIVE? Conclusion: 1. Discuss the results with your group. a. Describe your results, write a paragraph (or 2) describing what happened to each tube and what you saw happening. (THIS SHOULD BE IN PAST TENSE) 2. Is yeast alive? Write a paragraph (or2) using evidence from above?