Subject: Why do respiration rates of glucose, sucrose and lactose vary with yeast?

I am currently planning my biology coursework, and have many results, but am 
still puzzled as to why different sugars give differing outputs of carbon 
dioxide. I know that glucose is a monosaccharide, and can therefore enter 
glycolysis as it is. However, sucrose and lactose are disaccharides, and must 
be split into non-reducing sugars first in order to respired. But why is the 
amount of carbon dioxide evolved different for each substrate, even if the same 
concentrations and volumes are used with the same volume of yeast?

Re: Why do respiration rates of glucose, sucrose and lactose vary with yeast?