Anaerobic respiration in yeast

AIM: See the effect of temperature in anaerobic respiration of yeast by counting carbon dioxide bubbles.

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HYPHOTESIS: Anaerobic respiration in yeast will decrease as temperature increases.

VARIABLES: Independent: Temperature

Dependent: Rate of anaerobic respiration in yeast
Fix: Volume of sugar solution (40ml) , Concentration of sugar solution, yeast mass (2g), volume of solution of yeast & sugar all together (20ml)

Delivering tube
2 test tubes
2 beakers
Bunsen Burner
Tap Water
Thermometer (±0.1°)
Electronic Balance
Sugar Solution
Measuring Cylinder

1. Measure 40 ml of sugar solution with the measuring tube. Place the 40 ml on the big beaker

2. Measure 2 g of yeast using the electric balance. Place the 2 g on the beaker with the sugar solution

3. Stir the yeast-sugar solution (Solution A) using the glass stick until the yeast has completely dissolved

4. Separate Solution A into two 20 ml solutions (Solution A1 and Solution A2). To do so, measure 20 ml with the measuring tube and place them on a small beaker. Repeat the procedure with the other 20 ml.

5. Prepare a water bath on the Styrofoam cup. Using the thermomether, make sure the water bath has a temperature of 45°C.

6. Light the Bunsen burner. Heat solution A1 to a temperature of 40°C

7. Using the measuring cylinder, measure 15 ml of Solution A1 and place them on one of the boiling tubes. Cover the boiling tube with the delivery tube and place the other end of the delivery tube into a test tube which contains tap water

8. Count the number of CO2 bubbles coming out of the delivery tube. Record the number of bubbles which came out each minute (checking time with the stopwatch) 9. Repeat from step 5 with Solution A2, but this time heat the solution up to a temperature of 100°C instead of 40°C.


We may realize that our aim was successfully achieved because we were able to know the effect of anaerobic respiration in yeast in 2 temperatures: 40° & a boiling temperature (90°-100°). If we see our results we may see that in test tube B, the one with the boiling water, hasn?t produced CO2 bubbles, there is no bubbles because yeast is boiled, so yeast don’t breath because when it was boiled it was killed, that causes yeast to not to breath. By looking at the formula of anaerobic respiration in fungi (yeast) & bacteria:

We can see that yeast contains glucose, because if the product is CO2 , the have to contain glucose. If we see graph 1 we can see that the line that indicates de results for water at 40° is increasing as time passes. As I already mentioned, at a boiling temperature yeast don’t breath so we can say that as temperature increases less CO2 bubbles are produced, so less respiration is done by yeast.

EVALUATION: One way in which we may improve the experiment is by doing different ranges of temperatures, & changing the volume of yeast it would be interesting for another experiment. One of the main source of uncertainty in this experiment is the observer because if you confuse the number of bubbles the results may be different, in another way the observer could be the source of uncertainty is by when reading the thermometer placed into the water, you may confuse and the results will not be the same because yeast will be placed in another temperature.

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