Effect of Respiration on Dissolved Oxygen Concentrations -- January, 2002

Teacher Hints:

Stirring counts! When using the Dissolved Oxygen Sensor, it is important to move a steady flow of test solution past the sensor’s membrane: while measuring, the sensor uses up dissolved O₂ molecules faster than they can diffuse back into the area. This creates a microenvironment next to the membrane that has a lower concentration of dissolved O₂ molecules than the test solution has in general. Therefore, the most effective way to ensure accurate results is to use a magnetic stir bar setup. Clamp the sensor in such a way that the tip of the probe is as close as possible to the magnetic stir bar.
PASPORT users: For simultaneous sensor measurements, we suggest using the USB 4-Port Hub (PS-2501) if your computer is not equipped with 2 USB ports.
Each student group will need approximately 5 mL of yeast solution. It may be easiest to assign one student at a central lab station the task of measuring and dispensing each lab group’s yeast sample into a small test tube.
5 gram samples of sugar can also be pre-measured and/or dispensed from a central location in the lab.
While recording data, one student can hold the Temperature Sensor in place while another student stirs the solution gently with the Dissolved Oxygen Sensor. Alternatively, one or both sensors can be held or suspended in place using clamps while the solution is stirred with a stirring rod.
To investigate the effect of temperature on cellular respiration, the process can be streamlined by assigning different lab groups a different starting temperature of oxygenated water. The class as a whole can then compare lab groups’ graphs to determine the effect of temperature on the yeast.
Many excellent references detailing and diagramming the processes of cellular respiration are available online. Encourage students to search the Internet for various graphical representations of respiration and photosynthesis, and/or to create their own graphics, concept maps, or posters.