Yeast is a single celled fungus that can respire aerobically when oxygen is available and anaerobically in the absence of oxygen.
Aerobic respiration in yeast:
Glucose + Oxygen ======> Carbon dioxide + Water
Anaerobic respiration in yeast:
Glucose ======> Ethanol and Carbon dioxide
Both forms of respiration produce carbon dioxide as a waste product so how could this be demonstrated experimentally?
This is the simplest set up that could demonstrate this. Lime water will go cloudy in the presence of carbon dioxide. Glucose solution is needed to provide the reactant sugar for the yeast to respire. The oil layer on the top is to prevent the diffusion of oxygen from the air into the Yeast in Glucose solution, this ensuring anaerobic respiration will occur.
What experimental factors could be altered in this set up?
Well assuming you keep the volume and concentration of lime water constant, the time taken for the limewater to go cloudy could be measured under differing conditions: the faster the time, the faster the rate of respiration. The experimenter could investigate the effect of changing the temperature, the pH or the concentration of glucose solution used. Make sure you understand how and why changing each of these factors might affect rates of respiration in yeast.