Cellular Respiration in Yeast

Adapted from “Alcoholic Fermentation in Yeast Investigation” in the School District of Philadelphia Biology Core Curriculum

© 2008 by Jennifer Doherty and Dr. Ingrid Waldon, University of Pennsylvania Biology Department

The Specific Lab Rubric “write up requirements” is located at the end of this document

Introduction

All living cells, including the cells in your body and the cells in yeast, need energy for cellular processes such as pumping molecules into or out of the cell or synthesizing needed molecules.  ATP is a special molecule which provides energy in a form that cells can use for cellular processes.

Cellular respiration is the process that cells use to transfer energy from the organic molecules in food to ATP.  The following equation summarizes the chemical changes that occur in cellular respiration of the monosaccharide glucose when oxygen is available

C6H12O6  +  6 O2  à  6 CO2  +  6 H2O   +  (up to) 38 ATP

The chemical reactions in cellular respiration are similar to the chemical reactions when organic chemicals are burned, but of course no ATP is produced.  Instead energy is released in the form of light and heat.  The following equation shows the chemical changes that occur when the monosaccharide glucose is burned.  Consider the similarities and differences between these equations.

C6H12O6  +  6 O2  à  6 CO2  +  6 H2O   +  light  +  heat

There is another important feature of cellular respiration which is not shown in these equations.  Cellular respiration involves many small steps; these multiple steps allow the cell to use the energy from each glucose molecules efficiently in order to make as many ATP molecules as possible.  The multiple steps of cellular respiration are described in your book and notes.  This lab focuses on how yeast perform cellular respiration in the absence of oxygen.  Remember if oxygen is present, glycolysis is followed by the Krebs cycle and electron transport chain, or aerobic respiration.  When oxygen is not present, glycolysis is followed by anaerobic respiration, aka fermentation.  Glycolysis is an anaerobic process.  It occurs regardless of the presence or absence of oxygen.  There are two types of fermentation, alcoholic and lactic acid.  The names come from the fate of the pyruvic acid formed at the end of glycolysis.  Which type of fermentation occurs depends on the organism.  The disadvantage of fermentation is that it produces fewer ATP molecules than aerobic respiration.  The advantage, however, is that glycolysis can continue, so at least some ATP is still being produced.

In this lab you will be using yeast.  You can grow yeast in a test tube filled with water that contains sucrose and is sealed with a balloon which creates an anaerobic environment.

Procedure (Note modifications due to smaller tube sizes 15 mL tubes)

1.        Your group will use four test tubes.  Label the test tubes (with masking  tape)  as follows and place them in the test tube rack:  0%, 1%, 5%, 10% (sucrose).

2.       Add 25 mL (7.5 mL) of the appropriate solution to each test tube.

3.       Place ¼ tsp. (0.75 grams) (1/8 tsp or 0.23 grams) of yeast to each tube.

4.       Put a balloon over the mouth of each test tube.

5.       Gently shake each tube until the yeast is dissolved.  Do not allow the solution to splatter up into the balloon.

Place the 4 tubes in an insulated cup filled with water at the assigned temperature. Use a thermometer to note the temperature during the 20 minutes.

6.       Measure the depth of bubbles produced in each tube every 2 minutes up to 20 minutes.  Observe and record the appearance of the balloon, as well as the circumference of the balloon in mm using a string and ruler.

7.       Once you have the initial set-up complete, write a hypothesis based on the procedure above and your knowledge of cellular respiration then predict what the outcome of the experiment will be.

(Note all of the following items will be part of your formal typed report)

Title

Hypothesis

Write your hypothesis in your journal.  Remember that a hypothesis is a testable model/explanation based on your prior knowledge about the experiment topic.  Your prediction below will be your guess about how the experiment will turn out. (2 pts)

Table 1: 

Title: ________________________________________________________

 

Depth of CO2 Bubbles After:

Sucrose Treatment

(record every 2 minutes in mm)

0%

 

1%

 

5%

 

10%

 

 

Table 2: Title: ______________________________________________________

 

Appearance of Balloon After:

Sucrose Treatment

every 2 minutes measure circumference of balloon in mm

Additional observations

0%

 

 

1%

 

 

5%

 

 

10%

 

 

 

Graph 1: Title ______________________________________________

(Using the data from the first data table to create a x-y scatter plot and provide the trend lines (for each concentration of sucrose), and the trend line equations, make sure your axes are labeled with units)

Calculations , calculate the rate of reaction at each temperature (using class data), handwritten with appropriate units.

Write up Requirements 40 points (for a general idea of what is being looked for in a well written lab report please see: AdaptedGeneric_Lab_Rubric2013.htm

A minimum of 2 references are required for this write-up. Use APA format as shown on www.bibme.org

1) Title  (4 point)

2) one general hypothesis (if...then...because, no pronouns) and purpose of the activity (4 points)

3) Two Data Tables (remember to number figures) data table #1: data with mm of foam, data table #2: balloon observations and circumference in mm (8 points)

4) 1 graph of your data with trend lines and equations (NOTE: if you use another lab table's data please give them credit below your graph) (4 points)

5) hand calculations of rates between at least TWO different concentrations (example: 10% vs 5% , 5% vs 1%, etc.) (with appropriate units) (4 points)

    Conclusion Questions (8 points)

    (Remember to write in complete sentences, avoiding all pronouns. Use data from the activity to support the answers. ) You can use the “power conclusion” format if you wish.

    1.What is sucrose?

    2.What was the independent variable(s) in the experiment?

    3.What was the dependent variable(s) in the experiment?

    4.What was the control setup of the experiment?

    5.What is the purpose of the control in any experiment?

    6.Did the yeast produce different amounts of carbon dioxide with different sucrose concentrations?Did the yeast produce different amounts of carbon dioxide at different temperatures? Explain why or why not there was a difference using knowledge from the reading assignments about cellular respiration?

    7.Was the prediction in the hypothesis supported by the data?    Explain.  How could the hypothesis be revised?  If so, why?

    8. What would be the next logical experiment?  Give a brief description of the "next" experiment.

  1. References (APA) (4 points)

  2. Mechanics and Grammar (4 points)

EXTRA CREDIT CHALLENGE: (4 points)

Create a graph that shows not only the different rates (slopes) of carbon dioxide generated at different sucrose concentrations but at different temperatures.