Respiration Exp.s Flashcards
Describe the method for an experiment to investigate the rate of aerobic respiration in yeast. (1)
1) Put a known volume and concentration of substrate solution (e.g. glucose) in a test tube. Add a known volume of buffer solution to keep the pH constant.
2) Place the test tube in a water bath set to one of the temperatures being investigated.
- Leave it there for 10 minutes to allow the temperature of the substrate to stabilise.
- Add a known mass of dried yeast to the test tube and stir for two minutes.
Describe the method for an experiment to investigate the rate of aerobic respiration in yeast. (2)
- Put a bung with a tube attached to a gas syringe in the top of the test tube.
- The gas syringe should be set to zero.
- Start a stop watch as soon as the
bung has been put in the test tube. - At regular time intervals (e.g. every minute), record the volume of CO2 that is present in the gas syringe. Do this for a set amount of time (e.g. 10 minutes).
How does the exp. to investigate the rate of aerobic resp. work?
As the yeast respire, the CO2 formed will travel up the tube and into the gas syringe, which is used to measure the volume of CO2 released.
How often do you need to repeat the exp. to calc a mean?
(aerobic respiration exp. )
- repeat the experiment three times at each temperature you’re investigating.
- to calculate the mean at each temperature.
How could you change the aerobic respiration exp. to make it run for more time (or with more yeast or glucose)?
Use a conical flask to trap more oxygen.
What is the control exp. for the aerobic resp. exp. ?
A control experiment should also be set up at each temperature, where no yeast is present. No CO2 should be formed without the yeast.
How does the exp. to calc the rate of anaerobic respiration differ to the aerobic exp.?
After the yeast has dissolved into the substrate solution, trickle some liquid paraffin down the inside of the test tube so that it covers the surface of the solution.
This will stop oxygen getting in, which will force the yeast to respire anaerobically.
What other variable could you effecting the rate of respiration could you investigate using this method?
Substrate conc.
Different respiratory substrate
Optimum pH
A student was trying to find the optimum pH for yeast to produce ethanol. She set up three test tubes each containing a solution of glucose buffered to a different pH.
She then dissolved some yeast in the solution and trickled some liquid paraffin down the inside of the the test tubes.
Immediately after, she put a bung in the top of each test tube, with a tube attached to a gas syringe.
Every 60 seconds, she recorded how much CO2 had been released into the gas syringe.
Why would measuring the rate of CO, production help her to find out how quickly ethanol was being produced?
Measuring how fast CO2 is produced would indicate how far ethanol is being produced.
A student was trying to find the optimum pH for yeast to produce ethanol. She set up three test tubes each containing a solution of glucose buffered to a different pH.
She then dissolved some yeast in the solution and trickled some liquid paraffin down the inside of the the test tubes.
Immediately after, she put a bung in the top of each test tube, with a tube attached to a gas syringe.
Every 60 seconds, she recorded how much CO2 had been released into the gas syringe.
Give two variables that should have been controlled in this experiment and describe how each of these variables should have been controlled.
- Temp. - water bath
- Mass of yeast used - weighing out a set amount of yeast into each test tube.
- Vol./conc. of glucose solution - using a known vol. of glucose solution/ a fixed conc. of glucose solution.
A student was trying to find the optimum pH for yeast to produce ethanol. She set up three test tubes each containing a solution of glucose buffered to a different pH.
She then dissolved some yeast in the solution and trickled some liquid paraffin down the inside of the the test tubes.
Immediately after, she put a bung in the top of each test tube, with a tube attached to a gas syringe.
Every 60 seconds, she recorded how much CO2 had been released into the gas syringe.
What negative control should have been included in this experiment and why?
A control tube should be set up for each pH being investigated.
Contain glucose but no yeast.
No CO2 should be produced.
Allows the student to check any CO2 being released in the other tubes is actually being produced by the yeast.
