Question

How to explain an experiment result that the rate of respiration of yeast with water is faster than that with starch solution? Probably yeast can respire in water with endogenous substrates but no sugar. I predicted that yeast would respire in starch solution faster than that in water.But now I cannot understand the experiment result. Is the starch solution unfavorable for the respiration?

Answer 1

yeast cannot dissolve starch. yeast can dissolve mono- and dissacharides but not polysaccharides (or at least not efficient enough) to gain energy from it. that is why brewing beer is more difficult than making wine, since in grain you have starch that you first have to destroy so that the yeast can digest it, while in grapes you have sugar.
so if you put starch to yeast, the yeast cannot digest it properly. that's why it does not respire with starch.
why it respires with normal water? i don't know. i would say there was something in the water that provided the yeast with sugar, otherwise it might not have had respired