RP 9 - Respiration in Single-Celled Organisms

• Yeast is a single-celled organism that respires both aerobically and anaerobically.
• During respiration, electrons are transferred to synthesise ATP.
• Respiration can be measured using a redox indicator dye such as methylene blue, which accepts these electrons and undergoes a colour change from blue to colourless.
• The equipment list for this investigation includes Yeast and glucose in buffered solution, Water bath, Thermometer/temperature probe, Test tubes, and Timer.
• In this method, the named variable is temperature.
• Set up a water bath at 35°C.
• Add 5cm3 of the yeast and glucose solution to three test tubes and place them in the water bath to equilibrate for 10 minutes.
• Add 2cm3 of methylene blue to the test tubes and start the timer.
• Shake for 10 seconds and place the test tube back in the water bath.
• Record how long it takes for the methylene blue to turn colourless for each test tube.
• Repeat the experiment using temperatures of 40°C, 50°C, 60°C, and 70°C.
• Find the mean of the results for each temperature and use it to calculate the average rate of respiration.
• The yeast and glucose solution should be buffered to maintain a constant pH.
• Yeast has an optimum temperature range for respiration, which is shown by the peak on the graph.
• As the temperature moves away from the optimum, the rate of reaction will decrease as enzyme action decreases, and at high temperatures denaturation may occur.
• As enzymes are crucial to respiration, as their activity decreases, so does the rate of respiration.
• This means that the methylene blue will take longer to turn colourless when the temperature is further from the optimum.