Required Practical 8 - Investigation of a specific variable such as substrate or temperature on the rate of respiration of a suitable organism such as yeast or a locust

What is the apparatus needed for the experiment for yeast?

Apparatus needed:

Yeast

Glucose solution

Test tubes

Stopwatch

DCPIP

Describe the method of this experiment?

Method:

Add a set volume of yeast suspension to test tubes containing a certain concentration of glucose

Put the test tube in a temperature-controlled water bath and leave for 5 minutes to ensure the water temperature is correct and not continuing to increase or decrease

Add a set volume of DCPIP to the test tube and start the stopwatch immediately

Stop the stopwatch when the solution becomes colourless or lose all blue colour

This is subjective and therefore the same person should be assigned this task for all repeat experiments

Record the time taken for a colour change to occur once the dye is added

Repeat across a range of temperatures. For example, 30C, 35C, 40C, 45C

How do you calculate the rate of respiration?

The rate of respiration is inversely proportional to the time taken.

For living organisms/other method:

What would you use to test this experiment with living organisms?

Respirometers are used to measure and investigate the rate of oxygen consumption during aerobic respiration in organisms

By adding the apparatus to a thermostatically controlled water bath the effect of temperature on the rate of respiration can be investigated

The experiments usually involve organisms such as germinating seeds or invertebrates

Describe the method for this experiment?

Measure oxygen consumption: set up the respirometer and run the experiment with both tubes in a controlled temperature water bath. Use the manometer reading to calculate the change in gas volume within a given time, x cm3 min-1

Reset the apparatus: Allow air to reenter the tubes via the screw cap and reset the manometer fluid using the syringe. Change the temperature of the water bath and allow the tubes to acclimate, then close the screw clip to begin the experiment

Run the experiment again: use the manometer reading to calculate the change in gas volume in a given time, y cm3 min-1

Repeat the experiment several times at different temperatures

How can you find out the volume of oxygen produced?

The volume of oxygen consumed (cm3 min-1) can be worked out using the diameter of the capillary tube r (cm) and the distance moved by the manometer fluid h (cm) in a minute using the formula:

πr2h

How do you prevent any leaks?

Close tightly w/ bung

How do you prevent the change in temperature/the expansion

Place in a water bath

How do you prevent no change in volume?

Add NaOH to absorb all CO2 so only change in volume of Oxygen is measured