respiration experiments

Question 1

what type of organisms can you investigate factors affecting aerobic respiration

Answer 1

single celled organisms

Question 2

what is an example of a single celled organism that you can investigate factors affecting aerobic respiration

Answer 2

Yeast are single -celled organisms that can be grown in culture. They can respire aerobically when plenty of
oxygen is available and anaerobically when oxygen isn’t available. Both aerobic and anaerobic respiration in
yeast produce C 0 2, so the rate of C 0 2 pro duction gives an indication of the yeast’s respiration rate.

Question 3

what is one way to measure C02

Answer 3

One way to

measure CO2 production is by using a gas syringe to collect the CO2

Question 4

what is step 1 of investigating how temperature affects yeast aerobic respiration

Answer 4

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. (Choose the optimum p H for the yeast y o u ’re testing — usually 4 -6 .)

Question 5

what is step 2 of investigating how temperature affects yeast aerobic respiration

Answer 5

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.

Question 6

what is step 3 of investigating how temperature affects yeast aerobic respiration

Answer 6

Add a known mass of dried yeast (e.g. Saccharomyces

cerevisiae) to the test tube and stir for two minutes.

Question 7

what is step 4 of investigating how temperature affects yeast aerobic respiration

Answer 7

After the yeast has dissolved into the solution, 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

Question 8

what is step 5 of investigating how temperature affects yeast aerobic respiration

Answer 8

Start a stop watch as soon as the

bung has been put in the test tube.

Question 9

what is step 6 of investigating how temperature affects yeast aerobic respiration

Answer 9

As the yeast respire, the C02 formed will travel up the tube and into
the gas syringe, which is used to measure the volume of C02 released.

Question 10

what is step 7 of investigating how temperature affects yeast aerobic respiration

Answer 10

At regular time intervals (e.g. every minute), record
the volume of C02 that is present in the gas syringe.
Do this for a set amount of time (e.g. 10 minutes).

Question 11

what is step 8 of investigating how temperature affects yeast aerobic respiration

Answer 11

A control experiment should also be set up at each temperature, where
no yeast is present. No C02 should be formed without the yeast.

Question 12

what is step 9 of investigating how temperature affects yeast aerobic respiration

Answer 12

Repeat the experiment three times at each temperature
you’re investigating. Use your data to calculate the mean
rate of C02 production at each temperature.

Question 13

what is step 1 of investigating how yeast anaerobic respiration is affected by temperature

Answer 13

Set up the apparatus according to

steps 1-3 of the aerobic yeast temp (c) experiment

Question 14

what is step 2 of investigating how yeast anaerobic respiration is affected by temperature

Answer 14

After the yeast has dissolved into the substrate
solution, trickle some liquid paraffin down the
inside of the test tube so that it settles on and
completely covers the surface of the solution.
This w ill stop oxygen getting in, which will
force the yeast to respire anaerobically.

Question 15

what is step 3 of investigating how yeast anaerobic respiration is affected by temperature

Answer 15

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.

Question 16

what is step 4 of investigating how yeast anaerobic respiration is affected by temperature

Answer 16

Perform steps 5-9 from the temperature yeast aerobic respiration method

Question 17

how can you adapt these methods to investigate other variables

Answer 17

You can also easily adapt these methods to investigate the effects of other variables, such as substrate
concentration and the use of different respiratory substrates (e.g. sucrose) on the respiration rate.
Just remember that you should only change one variable at a time (the independent variable, see page 208).
All the other variables that could affect your results need to be controlled (kept the same) or your results
won’t be valid.