Biology, Answering the Big Questions of Life/Fermentation student lab

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Collecting CO2 from Yeast fermentation

Fermentation lab

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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.

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.


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A. Make the yeast cultures

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  1. Measure 10ml of sugar
  2. Place into labeled 500ml Erlenmeyer flask and fill to 200ml with warm water. Mix well. Cover tube.
  3. Add 1 package of rapid rise yeast to flask and mix briefly.
  4. Pour some of the mixture into a small beaker to test.
  5. Place a balloon over the mouth of the flask.

B. Observe yeast cultures

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  1. Allow yeast to grow for at least 30 minutes.
  2. Look at the balloons on the flasks. Observe changes if any.
  3. Take a bit 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
  4. Let slide sit for 5 minutes, and observe. Are there air bubbles under the slide? Explain.


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1 Write the equation for anaerobic fermentation starting with glucose. Label the reactants and the products. C6H12O6 =CO2 +C2H5OH

2. Draw the equation that shows the result of aerobic respiration.

C6H12O6 +O2 =CO2 +H2O

3. What was the glucose concentration in each flask when you started?

4. What was the glucose concentration in each flask when you ended?

5. Was there any difference?

6. If so, why do you think that one flask had less Glucose?

7. Why does ethanol burn when water does not?

8. Name two foods that are fermented.

9. Why is wine stored in sealed casks?

10. Draw a picture of budding yeast cells.