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Anaerobic respiration can be demonstrated by removing oxygen from yeast’s surroundings.

Procedure

1. Boil the glucose solution to sterilise it and remove any oxygen, leaving behind the glucose needed for anaerobic respiration.
2. Cool before adding the yeast (high temperatures will kill it).
3. Place a layer of oil on top of the glucose solution to prevent oxygen entering.
4. Yeast will respire anaerobically producing alcohol, heat and carbon dioxide that can be collected in limewater.

Practical 1.5 - Investigate factors affecting the respiration of yeast

Temperature - procedure

1. Mix yeast into a solution of glucose and water - this provides the glucose and oxygen needed for respiration.
2. Leave at room temperature for 1 hour.
3. Place mixture in a test tube.
4. Place a boiling tube over the test tube and invert - the test tube will now be upside down.
5. Place in water bath at 10°C.
6. Measure the height of the bubble at the top of the test tube.
7. After 30 minutes, measure the height of the bubble at the top of the test tube.
8. Repeat steps 2 to 7 at different temperatures (e.g. 20°C, 30°C, 40°C and 50°C).
9. Calculate the change in bubble height and record results in a table.
10. Draw a graph of the change in height against the temperature.

Results

The optimum temperature for respiration will produce the largest bubble of carbon dioxide after 30 minutes, as respiration will have happened fastest.

Different sugars - procedure

1. Mix yeast into a solution of glucose and water – this provides the glucose and oxygen needed for respiration.
2. Leave at room temperature for 1 hour.
3. Place mixture in a test tube.
4. Place a boiling tube over the test tube and invert - the test tube will now be upside down.
5. Place in water bath at 30°C.
6. Measure the height of the bubble at the top of the test tube.
7. After 30 minutes, measure the height of the bubble at the top of the test tube.
8. Repeat steps 1-7 with yeast mixtures in different sugars (e.g. sucrose, fructose, lactose, maltose).
9. Calculate the change in bubble height and record results in a table.