Experiments

Question 1

How do you investigate factors affecting respiration in single celled organisms

Answer 1

1. Put a known volume and concentration of substrate solution 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 been investigated. Leave it there for 10 minutes to allow the temperatures of the substrate to stabilise
3. Add a known mass of dried yeast to the test tube and stir for two minutes
4. After the yeast has dissolved into the solution, put a bung with a tube attached to the gas syringe in the top of the test tube. The gas syringe should be set to zero
5. 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
6. Start a stop watch as soon as the bung has been put in the test tube
7. 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
8. At regular time intervals, record the volume of co2 that is present in the gas syringe. Do this for a set time
9. A control experiment should also be set up at each temperature, where no yeast is present. No co2 should be formed without the yeast
10. Repeat the experiment 3 times at each temp you’re investigating. Use your data to calculate the mean and rate of co2 production

Question 2

How can the rate of oxygen consumption be measured using a respirometer

Answer 2

1. The apparatus is partially sub merged in a water bath for 15 degrees to provide the optimum temperature for the woodlice and therefore, the optimum temperature for the enzymes involved in their respiration
2. The control tube is set up in the exact same way as the woodlouse tube, except that the woodlice are substituted with glass beads of the same mass
3. For ten minutes, the tap is left open and the syringe is removed to allow the apparatus to equilibrate and the respiration rate of the woodlice to stabilise in their new environment
4. When ten minutes is up, the two is closed and the syringe is attached.
5. The syringe is used to reset the manometer, so that the ends of the fluid are at the same level on either side of the ‘U’ and the reading from the volume scale on the syringe is recorded
6. As respiration occurs, the volume of the air in the test tube containing woodlice will decrease, due to the oxygen consumed during respiration
7. The decrease in the volume of the air will reduce the pressure in the test tube, causing the coloured fluid in the capillary tube of the manometer to move towards it
8. After leaving the apparatus to run for a set period of time, the syringe is used to reset the manometer and the reading on the syringes volume scale is recorded again. The difference between this figure and the figure taken at the start of the experiment is the oxygen consumption for this time period. You can use this to calculate a rate of respiration
9. To check the precision of the results, the experiment is repeated and a mean volume of o2 is calculated