The Faker

Is yeast alive?

Every one use's yeast every day. What is yeast, and what are some common uses of yeast?

You can buy yeast to make bread in the grocery store.

Instructions to Test for Metabolism

Indirect: Not proceeding straight to the point or object

Molecules: The smallest particle of a substance that retains the chemical and physical properties of the substance and is composed of two or more atoms; a group of like or different atoms held together by chemical forces.

Carbon dioxide: A colorless, odorless, incombustible gas, CO2, formed during respiration, combustion, and organic decomposition and used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers, and aerosols. Also called carbonic acid gas

Metabolize: To subject (a substance) to metabolism.

To produce (a substance) by metabolism

I 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 as other living organisms.

When yeast, humans, and other living organisms use energy, they break down high-energy molecules like sugar to get the energy they need and give off a gas called carbon dioxide as a by-product of this reaction. We will test whether yeast can metabolize sugar and produce a gas which we will presume is carbon dioxide. Specifically, we will test whether yeast produces a gas when it has sugar available as a food vs. when no sugar is available.

Do you expect yeast to produce a gas when sugar is available? __________

Do you expect yeast to produce a gas when no sugar or other food is available?

__________

Explain the reasons for your predictions.

To test your predictions, use the following procedure.

1. Set up four test tubes in a test tube rack.

2. Label each tube with a number, 1-4. Test tubes 1 and 2 will both have yeast, sugar and water. Test tubes 3 and 4 will both have only yeast and water, with no sugar.

3. Add warm water to each test tube up to the first fill line.

4. Add sugar to tubes 1 and 2 until the water rises to the second fill line. These tubes will be your experimental group. Do not add sugar to tubes 3 and 4.

5. Now carefully add yeast to each tube until the water rises to the third fill line on tubes 1 and 2 and the second fill line on tubes 3 and 4.

6. Cover the opening of each test tube 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.

7. Observe what occurs in the test tubes and any changes in the balloons which cover each test tube every 5 minutes. Record your observations carefully in the table on the next page.

If the yeast grains are capable of metabolism, it will take some time to produce enough carbon dioxide to see the change in the balloons. While you are waiting for this change, set up the experiment to test