Lab 4: Fermentation

Fermentation lab
Spurthi Tarugu, Kavin Caldwell, Claudia Osorio
In this lab we will observe fermentation occurring in yeast cells. Yeast cells are fungal cells that can metabolize in two ways. In the presence of oxygen, they use aerobic respiration and break glucose down into CO2 and water. In the absence of oxygen, they ferment sugar creating CO2 and ethanol (ethyl alcohol).
We will take yeast cells and grow them absence of oxygen. We will test the glucose content before and after they are allowed to ferment and notice the difference if any.Background:
Respiration: The breakdown of sugar (glucose, the universal food molecule for all organisms) to form ATP (the universal energy storage molecule for all organisms). There are two types, aerobic and anaerobic (also called fermentation).Background Information: There are two types of respiration: aerobic (requiring oxygen) and anaerobic (without oxygen).Yeast cells (a type of fungus) obtain energy from glucose (sugar) by a specific anaerobic process called fermentation. There are two types of fermentation: lactic acid fermentation (which occurs in muscle cells when they are oxygen-deprived), and alcoholic fermentation, which is involved in the making of food products. Alcoholic fermentation begins after glucose diffuses into the yeast cell. The glucose is broken down into 2, 3-carbon molecules called pyruvic acid. The pyruvic acid is then converted to CO2, ethanol, and energy for the yeast cell. Fermentation is used to make a variety of food products, including the making of beer, wine, bread, cheese, sauerkraut, and baked goods. It is the carbon dioxide produced by the yeasts that give fermented drinks their”fizz.”Equation for alcoholic respiration:
C6H12O6 → 2C2H5OH + 2CO2 (1 molecule of glucose is converted to 2 ethanols and 2 carbon dioxides)
A. Make the yeast cultures

  1. Measure 10ml of sugar by volume.
  2. Place into labeled 250 ml Erlenmeyer flask and fill to 150 ml with warm tap water. Mix well.
  3. Add 1 package of rapid rise yeast to flask and mix briefly.
  4. Pour 20 ml of the mixture into a small beaker to test.
  5. Place a balloon over the mouth of the flask with the remaining yeast mixture.
  6. Test 5 ml of the contents in the small beaker for glucose using the Benedict’s test.  Is it positive or negative?  How do you know?  The test is positive. We know that this is positive because the solution is no longer blue.

B. Observe yeast cultures

  1. Allow yeast to grow for at least 30 minutes.
  2. During this time, look at the balloons on the flasks. Observe changes if any. The balloon is inflating. The yeast scum is gathering at the top of the Erlenmeyer flask, and this layer is growing larger and larger over time.
  3. After 30 minutes, take a drop of brown yeast “scum” and make a wet mount slide. Observe at 400x. See if you can see the budding action of yeast cell division. ( Do not dye with Iodine, this will kill the cells!) Draw what you see.
  4. Let slide sit for 5 minutes, and observe. Are there air bubbles under the slide?  Why or why not?  Yes there are bubbles under the slide because this process releases CO2.
  5. Test the contents for glucose using 5 ml of the contents in the small beaker using the Benedict’s test.  Is it positive or negative? Positive. The sugar is present in the content.
  6. Clean your work area and wash your glassware.

Analysis Questions
1. Write the equation for anaerobic fermentation starting with glucose. Label the reactants and the products.

C6H12O6 → 2C2H5OH + 2CO2 +  2 ATP

Reactant → Products

2. Write the equation for aerobic respiration. Label the reactants and products.

C6H12O6  +  6O2  →    6CO2  +  6 H2O +  36 or 38 ATP
Reactant →  Products

3. Was glucose present when you started each test?  Explain.
Yes glucose was present in the sugar that we measured at the beginning of the test.
4. Was glucose present when you ended the test? Explain.
Yes glucose was present when we ended the test, and we found this out by doing a Benedict’s test.
5. Name the types of organisms that use fermentation all the time.
Yeast and bacteria use fermentation all the time.
6. Insert a Venn Diagram comparing and contrasting the two types of fermentation.
The types of fermentation are lactic acid fermentation and alcohol fermentation.

7. Name two foods that are a result of fermentation.

Bread and alcohol are results of fermentation.

9. Why is wine stored in sealed casks?
Wine is stored in the sealed casks o keep the fermentation process going and to make sure that the gases released in the process remain inside the mixture.

10. Name at least two reasons why animal muscles use lactic acid fermentation instead of alcohol fermentation.
Animal muscles use lactic acid fermentation instead of alcohol fermentation because when a muscle goes through extreme exercise there is a lack of oxygen and lactic acid fermentation creates what the muscle needs to keep on functioning properly. The other reason is because the end product of alcohol fermentation is ethanol and CO2 which is harmful to the muscles.