Anaerobic respiration

Hmm, a teacher asked me what will be the result of this experiment. This experiment demostrated the effect of anaerobic respiration of yeast.

Yeast suspension is mixed with glucose and a layer of oil is added on top to ensure it is anaerobic. This is actually a question on a worksheet which ask what will happen to the limewater. Normal people will sure know that during anaerobic respiration, carbon dioxide will produce and it will pass through the delivery tube to make the limewater chalky. This is a correct answer.

However some "smart kid" who answer it that the lime water will not turn chalky as in their opinion, the layer of oil which prevent oxygen to enter should also prevent the carbon dioxide from escaping. So to prove this theory wrong and to confirm our answer we tried out this experiment. Practically, the limewater turn CHALKY. This shows that we are correct. What we can explain is that the carbon dioxide produce actually created a force to push itself through the oil. Remember my lava lamp experiment? Bubbles (carbon dioxide) will reach the top layer of the oil and burst, hence releasing the carbon dioxide gas into the space of the boiling tube which then bubbled into the limewater to make it chalky. This is also the reason that my lava lamp will have coloured bubbles passing through the oil. When the carbon dioxide burst, the colour carried with the carbon dioxide will sink down (due to gravity pull).

However diffusion of oxygen from the air do not have such force to push its way into the yeast and glucose suspension.

Conclusion : Limewater will turn chalky as the anaerobic respiration produce carbon dioxide and this exert a force which allow it to pass through the oil and bubbled into the limewater. Whereas diffusion of oxygen do not have a force to allow it to pass through the oil and hence this demostrated an anaerobic respiration.