IB Biology SL Experiment: The Effect of Temp. on rates of respiration by Yeast(Assessment of skills DCP & CE)

Aim
To measure the amount of CO2 produced at three different temperatures

To calculate the rate of respiration in each case.

To link the theory of enzyme activity and temperatures to respiration.

Hypothesis
As respiration is controlled by enzyme catalysed reactions the rate of respiration will increase as the temperature increases, up to the temperature which denatures the enzymes.

Apparatus

  • Access to 200ml of live yeast suspension.
  • Access to soda lime (granules)
  • One respirometer per group
  • Filter Paper
  • Scissors
  • Tweesers
  • Dropping Pipette
  • Thermometer

METHOD

  1. Half fill a 250ml beaker with cold water to use as a water bath.
    Record it's temperature, regularly to ensure that it remains constant.
  2. Label one of the respirometer boiling tubes 'live yeast' and the other 'water'.
  3. Put an equal amount of soda lime into each and then the wire basket.
  4. Cut two equal sized strips of filter paper as big as possible, but they must fit in the tubes – rolled up.
  5. Soak one filter paper in live active yeast and the other in distilled water for 1 minute.
  6. Put the paper into the boiling tubes.
  1. Connect the U-tube to the test tubes and adjust the 3-way taps to start the experiment.
  2. Start stopwatch, and time the absorption of gas by the live yeast. Stop when the bubble has moved a measurable distance.
  1. IF it doesn't work look for leaks and start again.
  2. IF it does work, reset the coloured liquid using the 3-way switches and repeat the experiment at least three times. (DON’T change the paper)
  1. Add hot water to the water bath to increase the temperature by 10°C and repeat steps 4 to 9. (Now you change the paper)
  1. Repeat step 11 until you have recorded 4 or 5 temperatures.

RESULTS
Keep notes of your results.... here ...think of the error analysis. & qualitative observations

DATA PROCESSING

Process the results to show the trends in your experiment.

CONCLUSION and EVALUATION

Introduction to Respirometers
A respirometer has an air-filled chamber in which living tissue is placed. A substance to absorb carbon dioxide produced is added. A tube along which a liquid flows shows changes in the oxygen volume in the chamber.


A more sophisticated respirometer

The respiring tissue could be; filter paper soaked in yeast solution, germinating peas or other seeds or invertebrates such as locusts or maggots.

The substance usually used to absorb carbon dioxide is soda lime; other alkalies such as sodium or potassium hydroxide (solid pellets or solution) could also be used. CAUTION: Alkalies are corrosive.

The apparatus is usually enclosed in a water bath to keep the temperature stable. Temperature is also a factor which is likely to have a major effect on the rate of respiration (and all metabolic activity). If the temperautre changes during the experiment the volume of gas will change through expansion or contraction.

The apparatus is set up as in the diagram, and the liquid level noted. The time taken for the liquid to travel a certain distance gives a measure of the amount of oxygen absorbed by the living tissue. This is a measure of the respiration rate. The carbon dioxide excreted by the living cells is absorbed by the soda lime.

Questions

  1. What is the purpose of the soda lime?
  2. In which direction does the liquid level move?
  3. Why is the liquid coloured?

What would be the advantage if the tube was made of capillary (narrow bore) tubing?