During alcoholic fermentation, yeast produces a group of enzymes (zymase complex) which breaks down sugars to carbon dioxide and ethanol.
Sugars are groups of carbohydrates which are classified into monosaccharides and disaccharides. The following are the common characters of monosaccharides and disaccharides.
- They are all organic compounds because they contain carbon.
- They all contain carbon, hydrogen and oxygen.
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Hydrogen and oxygen are arranged in the ratio 2:1. For example the molecular formula of glucose is C6H12O6, which means Glucose is made up of Carbon, Hydrogen and Oxygen and the ratio of hydrogen and oxygen is 2:1. The other examples are Fructose (C6H12O6), Galactose (C6H12O6) but their structural formulae are different and are shown below.
- The above sugars are called monosaccharides and they cannot be split into further simple sugars. There are some other set of sugars which are more complex than monosaccharides and they are called disaccharides. Each disaccharide is made up of two monosaccharides.
- The formation of the common dissacharides such as maltose, sucrose and lactose is as follows.
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Glucose + Glucose → Maltose + Water
MALTOSE
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Glucose + Fructose → Sucrose + Water
SUCROSE
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Glucose + Galactose → Lactose + Water
LACTOSE
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In all the above disaccharides, the molecular formulas is C12H22O11 but their structures are different.
While conducting my investigation, the intention is to find out which of the sugars (glucose, fructose, sucrose, maltose and lactose) metabolizes yeast the most.
Prediction
I predict that the amount of carbon dioxide produced from the metabolism of glucose with yeast will be much higher than the same metabolism of fructose, sucrose, maltose and lactose.
The chain form of D-Glucose
Space filling model of Glucose
Glucose is the simplest monosaccharide sugar therefore it has fewer bonds to be broken by the enzymes in the yeast. In addition, the reaction rates will much faster so more of the yeast will metabolize glucose at the same time. Even so, Glucose is a ubiquitous fuel in biology more widely used than fructose and other sugars.
Analysis
The volume of carbon dioxide produced was found out with the following equation:-
Start volume of water (cm³) – End volume of water (cm³) = Volume of Carbon Dioxide produced (cm³)
The average is the mean of the results from the 4 trials.
- From the bar chart, Fructose has a higher average value than Glucose with a difference of 0.025 cm³.
- Maltose differs from Sucrose with the same difference that of Glucose and Fructose i.e 0.025cm³.
- Lactose has the smallest plot area as well as the lowest average value.
Conclusion
From my analysis, the results do not support the prediction I had previously mentioned. Glucose and Fructose have the same molecular formula but have different structures. Therefore they are classified differently; Glucose being classified as an aldehyde (compound containing a carbonyl group with at least one hydrogen attached to it) and Fructose being classified as a ketone (compound containing carbonyl groups with two hydrocarbon groups attached to it). The following diagram shows this clearly:
To conclude, Fructose is metabolized more productively by yeast than Glucose, Sucrose, Maltose and Lactose. It may be because it’s easier to break down a ketonic structure i.e Fructose than an aldehyde structure i.e Glucose.
Evaluation
The results of this experiment do have a reasonable degree of accuracy. The burette measured the controlled variable i.e. amount of carbon dioxide produced so it had an accuracy of ± 0.1ml. The measurements of volume were easily and clearly read on the burette scale; therefore the recordings should have been accurate. My prediction clearly stated that glucose was to be metabolized more by the yeast but the results proved me wrong. According to the bar chart, Fructose had highest average value than Glucose. This was a genuine scientific anomaly that was unexpected. The scientific cause behind this anomaly has been explained earlier in the Conclusion. The reliability of this experiment would gather the same conclusion if repeated by another. This experiment removes the assumption of that glucose will produce the most carbon dioxide when metabolized by yeast. The procedure of this experiment was simple and straightforward but certain aspects of this investigation can be improved. By making changes to the value of the controlled variables might increase the reliability of this experiment. The time limit, used within to measure the amount of carbon dioxide produced can be lengthened to an hour. Increasing the amount of substrate (e.g fructose) also will prove optional. Repeating the experiment as much as possible is another good idea for more accurate results. The burette is the most accurate and suitable piece of equipment for this investigation so it would be unnecessary to change this method.
To extend this experiment, we could conduct a comparative study between a macromolecule (starch) and a micro molecule ( glucose). Starch suspension will be used to metabolize by yeast using the same method that was used for this experiment. In a beaker, that is clearly labeled STARCH, the two liquids (starch suspension and yeast) will be poured in and mixed with the stirring rod. Similarly, glucose solution will be metabolized by yeast in another beaker, labeled GLUCOSE on it. Within a certain time limit, the amount of carbon dioxide produced in each of the beakers will be measured and recorded. This is obtained by finding the difference in the start and end volumes of water in the upturned burette. The independent and controlled variables will remain the same just like it did for this experiment. The expected result is that glucose will undergo the most metabolism by yeast than starch. This is because glucose is already broken down in its simplest form whereas starch still needs to. The aim of this extension is find out whether the action of yeast is quicker on a substrate that has low molecular weight (glucose) or high molecular weight (starch).