Cellular Respiration Lab
Introduction
Yeast are single celled organisms that can be used experimentally to represent the activities of a basic
eukaryotic cell. In order for cellular respiration to occur the cell itself must have the genetic information
to build the proper enzymes to catalyse the break-down of the macromolecule provided as a food
source. We know that enzymes are necessary to catalyze all biochemical activities within a cell. We also
understand that the more break-down that must occur the slower the rate of metabolism will be
observed. If enzymes are not available then cellular respiration will not occur.
In other words, we can only open the “locks” that we have “keys” for. Without the “key” we can’t
unlock the energy within the molecule. The more locks we have to unlock, i.e. the more keys we need
to use, the longer it will take to unlock the energy stored within the molecule.
Cellular respiration can be summarized as:
Carbohydrate + O2  CO2 + H2O + many ATP
When the carbon dioxide gas is released most of it is lost from the solution as a gas to the atmosphere.
However, some of the dissolved carbon dioxide stays in solution and reacts with the hydrogen ions
present in natural water. This forms a weak acid known as carbonic acid. Therefore, it is logical that as
the rate of cellular respiration proceeds the concentration of forming carbonic acid would increase. It is
this fact we will use to indicate the metabolic rate of the yeast based on the various food sources.
Purpose:
To observe the cellular respiration of yeast based on three different carbohydrates
Materials:
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Test tubes
Test tube rack
Glucose Solution
Sucrose Solution
Lactose Solution
Litmus Solution
Sodium Hydroxide Solution
Graduated Cylinders
Yeast
Procedure:
1. Create a data table for your rough observations (see Results for the template)
2. Obtain three test tubes and rack. Label them “G”, “S”, and “L”
3. Using an electronic balance and weigh boat, measure 0.1g of dry yeast for each test tube.
Cellular Respiration Lab
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Using the graduated cylinder, add 1ml of litmus solution to all three test tubes
Use a graduated cylinder to add 10ml of glucose solution to test tube labeled “G”
Use a graduated cylinder to add 10ml of sucrose solution to the test tube labelled “S”
Use a graduated cylinder to add 10 ml of lactose solution to the test tube labelled “L”
Add 10 drops of sodium hydroxide solution to all three test tubes.
Gently agitate the contents of all three test tubes and observe the initial colour of the solutions.
Record further observations after 10 minutes. Repeat these observations for a total of 3 trials.
Clean all equipment
Results
Table: Cellular Respiration Activity
Time
Initial
Observations
10 minutes
20 Minutes
30 minutes
Conclusion
1. Based on your observation, which of the three sugars does yeast metabolism the easiest? Why?
2. While some sugars are better than others as a food source, it does not mean that yeast are able
to use only one kind of sugar as a food source. Based on observations, was the yeast able to use
all the sugars? Elaborate.
3. How did the pH indicator allow you to determine which sugar was the most effective used by
the yeast?
4. In this experiment, you testes the effect of three different carbohydrates on the rate of cellular
metabolism. What other factor might affect the rate of metabolism and how would you
incorporate it into the procedure if you were to do the experiment again?