Water displacement is a cheap and effective method for measuring the volume of a gas. It is typically used in high school or college laboratories in which more expensive equipment is not available. By making a respirometer from a glass pipette and aquarium tubing, the gas from biological and chemical experiments can be precisely measured. In this experiment, the carbon dioxide produced by yeast will be compared under differing experimental conditions.
- Skill level:
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Things you need
- 1ml glass pipettes
- Aquarium tubing
- 500ml glass beaker
- Hot water bath
- Respirometer clamps
- Four large glass test tubes
- Four small glass test tubes
- Dry yeast
- Lab marker pen
- Four timers
Prepare a standard sugar and yeast solution. Add two grams of sugar to 100ml of distilled water; this will create a 2% sugar solution. Pour one packet of yeast into a 1/2 cup of warm water and mix thoroughly. Allow the yeast solution 5-10 minutes to activate before proceeding.
Label four glass test tubes by the numbers 1 through 4.
Set up the samples according to the table below using a five ml pipette. Make sure to change the pipette tip when switching between the distilled water, yeast suspension and glucose solution to avoid contamination. As an example, tube #1 requires four ml of deionised water, zero ml of yeast suspension and three ml of glucose solution. Tube #2 requires six ml of deionised water, one ml of yeast suspension and zero ml of glucose solution. Tube #3 requires three ml of deionised water, one ml of yeast suspension and three ml of glucose solution. Tube #4 requires one ml of deionised water, three ml of yeast suspension and three ml of glucose solution.
1 2 3 4 Tube #
4 6 3 1 DI water (ml)
0 1 1 3 Yeast Suspension (ml)
3 0 3 3 Glucose solution (ml)
Roll the tubes back and forth in your hands to distribute the solution throughout the tube. Now place the four tubes in a 500ml beaker filled with water up to 5cm from the top. Put the 500ml beaker containing the sample tubes in a hot water bath set at 30 degrees Celsius for five minutes in order to "activate" the yeast.
Remove the 500ml beaker containing the sample tubes from the hot water bath after five minutes.
Place a one ml glass pipette in each of the four tubes. The bottom tip of each pipette should be at the bottom of each sample tube. Attach aquarium tubing to the top of each pipette.
Pull yeast solution to the one ml mark near the top of the one ml glass pipette by attaching the pipette pump to the end of the aquarium tubing. Clamp the aquarium tubing while the solution is at the one ml mark. This may take a few attempts, as the tubing must be airtight to keep the solution at the one ml mark.
Start a timer once the pipette has been sealed. Repeat Step 2 for each tube, starting an individual timer for each after the tube has been sealed. Alternatively, the time at which each tube has been sealed can be written down.
Measure how much the liquid in each pipette has decreased every two minutes. Since the pipette is closed off from the top, the only way for liquid to escape if for the pressure of the carbon dioxide in the top of the tube to push it out the bottom. This allows for a measurement of the gas volume by how much liquid has left the pipette.
Measure every two minutes for a total of twenty minutes. Now create a table for the data and a graph that compares how much carbon dioxide each solution produced.
Tips and warnings
- When closing off the pipettes it's helpful to have one person draw up the liquid while another clamps the aquarium tubing shut.
- Be careful to avoid breaking glass during this procedure, since most instruments involved are made from it. Perform every step carefully and with ease.
- Do not leave the hot water bath unobserved. If all of the water evaporates it could start a fire.
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