Principles of Biology

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Adding water and foods like table sugar/artificial sweetener reactivates Saccharomyces cerevisiae. After reactivation, the cells become metabolically active and are able to perform cellular respiration thus producing a gas called carbon dioxide which fills the bottle then inflates the balloon. The balloon that will inflate most is the one whose bottle has table sugar.


Lab 6 Cellular Respiration

Purpose: Conduct a kitchen science experiment to observe a living organism and its growth when given water and various kinds of food or no food. This growth may be observed by waste gas emitted due to cellular respiration.

Learning Outcomes:
  • Name and properly spell the genus and species of the organism used in the experiment
  • Draw the chemical structures of glucose and ATP
  • Name the end product of the glycolysis pathway and the beginning substrate of mitochondrial acetyl CoA pathway
  • Name the waste gas produced by cellular respiration
  • State a hypothesis of the experiment based on the materials being tested. The procedure has been provided to test your
  • Draw a properly labeled bar graph with appropriate scaling on the Y-axis, and unit labels on both X-axis and Y-axis.
  • Identify the independent variables, and dependent variable in this
  • Explain the results of the experimental findings then write a summary. Explain if the results supported or did not support your hypothesis



Background: Baker’s yeast is a living organism, Genus Saccharomyces and species cerevisiae, Saccharomyces cerevisiae. Saccharomyces cerevisiae is a member of the Fungi Kingdom, it is single celled, and classified as a eukaryote with a cell wall outside its plasma membrane.

Saccharomyces cerevisiae (baker’s yeast) sold in grocery stores is produced by removal of water and is metabolically inactive so it cannot produce energy for cellular operations and cannot grow and reproduce itself. Saccharomyces cerevisiae are reactivated by the addition of water and food such as table sugar. Once reactivated the yeast cells become metabolically active and are able to perform cellular respiration. In this experiment you will observe cellular respiration indirectly through production of gases emitted by Saccharomyces cerevisiae cells. This waste gas emitted by Saccharomyces cerevisiae is captured in a balloon and you will observe changes in balloon size, and in slurry formed by the yeast due to its metabolic activity.

What to do in this lab:

Read Module 6 study plan before completion of Lab 6.

You may do the lab by yourself or in a team of two students. To find a partner use the Classlist in D2L to send an email invite.

Review the materials section, the procedure section, and data table provided in this lab. Now you are ready to write a hypothesis that will be tested using the steps of the procedure provided. You will be testing cellular respiration in Saccharomyces cerevisiae when they are given no food (water only), table sugar food, and diet sugar food. The yeast given water and no food functions as a negative baseline control. This means that you can compare this sample to the other two samples given the different foods: table sugar, and diet sugar.

Write your hypothesis in the space below:


Using the procedure steps provided in this lab, you will perform the experiment by setting it up, then measuring in metric units of centimeters intervals of 5 minutes, 10 minutes, 15 minutes, and 30 minutes the size of the balloon (balloon height) and the height the slurry during this time. Once the 30 minute point has been reached you may stop the experiment. You will record the balloon height and slurry height in centimeters in the data table provided. At each time point take a picture to document your results so you will have 4 pictures: 1st 5 minutes, 2nd 10 minutes, 3rd 15 minutes, 4th 30 minutes.

What is slurry? Slurry is produced by the Baker’s yeast as result of its metabolic cellular respiration. Slurry is a frothy bubbly looking area on top of the watery solution the yeast cells are dissolved in. See image provided below.


Yeast in water and yeast slurry (reference: yeast slurry link)


Yeast in water solution

 Once the experiment is finished, look at your data in the data table and using both balloon height and slurry height draw a bar graph (no lines graphs please!). There will be two bars per time period. Start the scale on the y-axis at 0 cm. If you are unfamiliar how to draw a bar graph then review bar graph and how to draw one at this link and use this link to review independent variables and dependent variables.

Look at your bar graph and summarize what this data shows as result of the experimental procedure and write a summary explaining if the data shows support or no support of your hypothesis. Finally, answer questions given below and upload to Assignment Lab 6 by Wednesday Sept 22nd 11PM.

  • 3 tablespoons Active Dry Yeast (1 packet of yeast is .25 oz, or 2.25 teaspoon (tsp) – you will need to purchase 4 packets of yeast
  • 1-2 packets sugar or use tsps. of sugar. 1 packet = 2 tsp sugar and 2 packets = 4 tsps sugar
  • 1-2 packets artificial sweetener (Sweet-n-Low or Equal) – get these from local Starbucks for no cost/low cost if none available at home
  • 3 Balloons, 2.5 inch long and thin recommended – use same type of balloon for each sample, may be purchased at Dollar store
  • Tape to secure each balloon end to its bottle so balloon does not fly off once filled with the yeast’s waste gas
  • 3 empty soda bottles well-rinsed or water bottles without the caps
  • Funnel or rolled-up piece of paper to deliver the yeast to each bottle
  • Warm water from tap but not hot to the touch. If water temperature is too hot you will kill your yeast and they will not be reactivated. Use the same amount in each bottle, about 1 inch per bottle
  • Metric ruler or measuring tape in centimeter units


Methods procedure:
  1. View video showing process of what to expect in the lab 6 experiment: link. Do not follow the video’s instructions since it varies from the materials and procedure given in this
  2. Using the funnel or rolled piece of paper carefully add 1 tablespoon of dry yeast to each
  3. Label your bottles to correspond to the data table you need to complete (see Data Table next page).
  4. Next, add the different ‘sugar’ sources to individual Make sure you add the same amount of sugar source to each (i.e. use either 1 packet in each bottle or 2 packets in each bottle). Be sure to match the labels.
  5. Add about 1 inch of warm water (from the faucet, not too hot) to each
  6. Swirl well to mix yeast into solution.
  1. Place a balloon over the bottle opening. Be sure to completely cover the opening in bottle. Tape each balloon lip to the bottle neck so it does not fly off when the balloon is
  2. It is best to place the sample bottles in the sink during the data recording
  3. Observe the bottles and balloons carefully and continually. Using the table on next page, collect the appropriate data at the indicated time points. You should record the height of the balloon as well as the height of the yeast/sugar slurry in your bottle. Carefully record the timing of your data collection.
  4. Photograph your experiment at each data collection point: 5 min, 10 min, 15 min and 30 min. You will have 4 pictures by the end of the
  5. Stop the experiment when you reach the 30 minute mark and make your last data recording. After that you may pour out the contents of each sample in the sink and rinse out the bottle and
  6. Use the results recorded in the data table to draw a bar graph showing the changes in balloon height and slurry height over time. Bar graph may be drawn by hand – use a ruler to be neat with line drawing or use Excel spread sheet if you know how to draw a graph this way. All data from the data table will be shown on the bar graph. The graph will use consistent scaling on the y-axis. Both X-axis and y-axis must have label and y-axis label will also have
  7. Write a conclusion based on the experimental
Data Table


Time elapsed

5 minutes

Time elapsed

10 minutes

Time elapsed

15 minutes

Time elapsed

30 minutes


Sugar source




Balloon color


height (cm)

Slurry height (cm) Balloon

height (cm)

Slurry height (cm) Balloon

height (cm)

Slurry height (cm) Balloon

height (cm)

Slurry height (cm)
No sugar – negative control
Table sugar
Artificial sweetener


Questions to answer using your own words

  1. Explain a reason to monitor the yeast sample without sugar or diet sugar added. Why was this sample needed?
  2. Since yeast are eukaryotic, where do the metabolic pathways of glycolysis and cellular respiration occur in these organisms? You will be naming two locations in eukaryotic
  3. What is the purpose of glycolysis and cellular respiration? Why do eukaryotic cells have this pathway?
  4. Give an example of the use of energy products from cellular respiration by yeast to
  5. During cellular respiration, the energy of one molecule gets passed on to another molecule. Name the substrate molecule glycolysis begin with. Name the energy molecule produced by mitochondrial cellular respiration that will be used by cells to operate other metabolic
  6. What were you observing in the yeast and why? Relate your answer to the process of cellular respiration.
  7. Name the independent and dependent variables in this
  8. Did anything surprise you about your results?
How to write the Lab 6 report
  1. Hypothesis of lab
  2. Completed data table with your recorded data will be in the report
  3. Complete bar graph with all data from data table
  4. Summary of experimental results and explanation if hypothesis is supported or not supported
  5. Four pictures: one picture per time point: 5 minutes, 10 minutes, 15 minutes, and 30 minutes. Pictures must be copied into the lab report and are not accepted as separate images. You will be asked to revise your work if this step is not
  6. Completed questions answered in your own
  7. Upload report to Assignment Lab 6 by Wednesday September 22, 11PM. If work in team of two students then upload one report with each student’s name in the


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