Biol 1440, Principles of Biology I

Principles of Cellular Processes
Aerobic Respiration


Aerobic respiration is the key metabolic process of producing cellular energy in eukaryotic and some prokaryotic cells.

Chemical Equation:
Glucose (C6H12O6) + 6 O2  wpe3.jpg (792 bytes)   6CO2 +6H2O


1. Develop a hypothesis and design an experiment on aerobic respiration of a single cell organism, yeast

2. Examine various components of the respiratory pathway such as Carbon source (substrate concentration), temperature,  and metabolic factors can affect respiration rates.

Research Questions

1. How many ways could you measure aerobic respiration?

2. Do plants undergo aerobic respiration? What cell organelle would a plant need for respiration? Would a fungus have the same or a different organelle?

3. How does temperature relate to respiration rate?  Is it similar to the effects observed with enzyme activity?

4.  How could you measure the effects of the various pathway components on the rate of aerobic respiration?

  • Which pathway component produces the most CO2/glucose? Glycolysis, Kreb's cycle, electron transport?



Campbell: pp. 147-153

CO2 Sensor Operation

Aerobic Respiration
Comparison of Respiration with Photosynthesis

Yeast Biology                         

Directed Investigation


Suggested volume for all runs is 50mL, but students can reduce it to a minimum of 20mL.

Directed Investigation-How much yeast is needed to get a respiration rate of 500-800ppm CO2/min?

1.       Yeast should be suspended in no more than 100mM glucose by diluting your stock solution.  The final volume should be no more than 50mL.

2.       Add varing amounts of yeast to your glucose solution and record the yeast concentration in mg yeast/mL.  Begin with a dilution range of 1/10 to 1/100.

3.       Yeast need at least 5 min to begin active respiration.

4.       Add respiring yeast to a clean 125mL flask with a stir bar just before data collection to avoid flask from building up high levels of CO2.

5.       Adjust the speed of the stir plate so that the solution is visibly moving to just forming a slight whirlpool.

6.       A data collection table should be constructed before beginning.

7.       A minimum of 10 CO2 readings or 2 min. of data collection should be used to calculate aerobic respiration rate, AR-rate (ppm CO2/min).

8.       Remember to fan the sensor down to ambient CO2 levels below 500ppm before beginning a new run.


1.       Select the CO2 sensor from the Vernier Experiment file.

2.       Under Sensor menu, set up the sensor to record time in minutes

3.       Sample 10-12X/min or every 10 sec.  Every 5 sec is OK.

4.       Duration 3-5 min or stop if ppm is 4500 or greater.  Sensor limit is 5000ppm.

Do NOT Breath Directly on the Sensor


Unplug CO2 Sensor after lab


Open-ended Investigation

Based on your group’s preliminary results and observations, develop a group hypothesis and detailed experimental design to study aerobic respiration in yeast. Your design should answer the following questions:
  • What research question is being answered by your hypothesis?
  • What is the hypothesis?
  • What are the treatments and/or variables and how will they be measured?
  • How many replications are needed?
  • What will an experimental unit consist of?
  • How will the data be presented?

Design and perform one of the following investigations


1.      What is the range and optimal temperature, C, for aerobic respiration in yeast? 

2.      How much does the rate of respiration change with a 10 C change in temperature? 

3.      What does a plot of AR-rate by temperature look like?

Complex C source
Glucose is a component of the disaccharides, sucrose and lactose.  In sucrose the second sugar is fructose and in lactose the second sugar is galactose.  Both are found in bread, if cane sugar (sucrose) and milk (lactose) are used.

1.      How does the AR-rate of the two dissachardes compare to glucose?

2.      How does the AR-rate compare between sucrose and lactose?

3.      What would cause the difference in rates?

Respiration Inhibitor

1.       How does azide affect aerobic respiration?  What part of the pathway and which cell component is most affected?
Respiratory chain inhibitors

2.       How much azide is needed to reduce AR-rate 50%?

3.       What would a plot of AR-rate by azide concentration look like?

Osmotic Effects

1.  In previous labs, students observed lower AR-rates as glucose concentrations increased, could this be due to an osmotic effect?

2.  Mannitol a sugar-like substance is often used to measure osmotic effects on cells because it is not readily metabolized.  What treatments would you need using a stock solution of 1M, which is about 20% mannitol?  

Remember that you would have to have a glucose in the AR-medium in order to have an AR-rate and that it would contribute to the osmolarity of the overall media.  Thus, every treatment would have some glucose (~20-50mM glucose). 

Alcohol Effects

1.  Although yeast make alcohol from anaerobic respiration, if exposed to O2 again they return ethyl alcohol to acetic acid and produce vinegar.  Does alcohol affect AR-rate of yeast enzymes?

2.  What concentration ranges would you have to test?  Yeast will ferment grapes into wine up to about 12% ethyl alcohol, and few,if any yeast can survive concentrations above 20%.



Students need a working 3.5 in floppy disk. Bring several to check, if necessary.

Your experimental design.