Does the Respiration Rate of Yeast Vary with Different Sugars

The aim of our investigation is to find out whether the use of different sugar isomers with yeast, will affect the rate at which the yeast respires at. The sugars to be tested are fructose, galactose, glucose, lactose and sucrose. Their effects on the respiration rate of yeast to be observed through the measurement (cm3) of the displaced water, which will tell us how much CO2 has been respired over 2 minutes. To compare the effects an average will be calculated for each and a result will be drawn from which we can draw a conclusion as to the effects, if any, of different isomers of sugar, on the respiration rate of yeast.
The simpler the sugar isomer is the higher the rate of respiration of the yeast. I believe there will be a 75% difference between the simple sugars glucose, galactose and fructose respiration rate, to the disaccharides: lactose, sucrose respiration rate.
An isomer is a compound with the same molecular formula but different structural formula. (1) We can tell by looking at the structures of the chosen sugars, that glucose, galactose and fructose are monosaccharide structural isomers of each other(14); sharing the same basic molecular formula with different atomic arrangements. Monosaccharide’s are the simplest form a sugar can be in; It can therefore be hydrolysed no further (15). Contrastingly, lactose and sucrose are disaccharides, they are 2 monosaccharide isomers joined together by a glycosidic link (2). They are double ringed molecules, and are consequently larger. Lactose and sucrose have the same chemical formula, contrasting structurally to each other, making them structural isomers to each other. By identifying a structural split in our sugars, we can predict that there will be a difference in their ability to react and therefore respire.
Because in respiration glucose needs to be in the simplest form possible; as evident in the respiration equation: glucose + oxygen → carbon dioxide + water (+ energy) (16), we can assume lactose and sucrose will respire the slowest as they will first need to be hydrolysed to their simplest monosaccharide forms in order to go through respiration. Research from Ron Baker Ph.D. supports this prediction; he states how if the yeast used doesn’t produce an enzyme (beta-galactase) which breaks down the disaccharide to a monosaccharide, then it is unable to use it as an energy source. (17) We can predict lactose to be least likely to produce a reaction.
However, isomers do not necessarily share the same properties unless they have the same functional group (1). A functional group (Anne Marie Helmenstine, Ph.D. (3)) is a group of atoms found within molecules and are the cause of the chemical reaction characteristics of that molecule. Therefore, we can also predict that the chosen sugars will react differently due to the differences in their functional groups, as well as their structures. (4)

(7)

(8)

(10)

(12)

The research from Ron Baker Ph.D. (17) is made clear here(10) because without the enzyme( beta-galactase) to break the disaccharide into monosaccharides, their functional groups are not exposed and they are therefore unable to react and therefore respire.
Sucrose however will be able to respire due to the exposure of its functional group however because it is a larger