Cellular Respiration And Fermentation
This scientific report will be based on cellular respiration, or fermentation. In specific, how the type of sugar affects the rate of fermentation. The aim of this experiment was to find which type of sugar was best suited to produce ethanol. In the experiment, four different sugars were used, they included sucrose, glucose, lactose and fructose. This research is still relevant today, as alcohol is still consumed and is required on a large scale. This makes it crucial to companies to find the best sugar to use in the fermentation process.
Cellular respiration is a process that living organisms undergo to create and obtain chemical energy in the form of adenosine triphosphate (ATP). The energy can be gained in two different forms of cellular …show more content…
respiration, called aerobic respiration and anaerobic respiration, also called fermentation. Glycolysis is the first stage of both anaerobic and aerobic respiration. This stage uses 10 different enzymes to turn glucose into pyruvate acid. After glycolysis, the two different forms diverge. The cell desires to preform aerobic respiration which grants the cell 36-38 ATP, however this requires oxygen. Fermentation is a process implemented by organisms to obtain ATP without the use of oxygen, however this produces only 4 ATP. When yeast is in the presence of oxygen it performs aerobic respiration, but when oxygen is absent it undergoes fermentation. In fermentation, the pyruvate acid is then converted into ethanol alcohol in two stages. In the first stage, it is converted into acetaldehyde with the release of carbon dioxide (CO2) as a byproduct, which will be used to measure the independent variable of the experiment, which is created in the second stage. This this stage the acetaldehyde is converted to ethanol. (IUPUI Dep. of Biology, 2004)
Before fermentation, glycolysis occurs. 10 enzymes are used during this process, and the initial enzyme in the process, called hexokinase, breaks down glucose and ATP into glucose-6-phosphate, ATP and hydrogen s (Spark Notes, 2016). During fermentation, 2 enzymes are used. They are pyruvate decarboxylase and alcohol dehydrogenase. Enzymes are specialized proteins used to catalyse reactions. This means the enzyme reduces the amount of energy required to perform the reaction this is called the activation energy. Enzymes do this with an active site, which is shaped to fit one specific molecule, and cannot be used to as a catalyst for any other molecules (Department of Forestry and Plant Physiology Program, University of Kentucky, Lexington, 1987). The enzymes have a primary, secondary and tertiary structures. The primary structure consists of the amino acids of the peptide bond that bonds them together. These are covalent bonds formed between C=O and N-H groups of the amino acids. The secondary structure appears as a double helix. It consists of the hydrogen bonds that form between the oxygen of the C=O in the strand and the hydrogen of the N-H group four amino acids below it in the helix.
These enzymes have acidic R groups in their amino acids, meaning the enzymes perform better in acidic conditions. This means the pH of the solution must be taken into account to ensure this is a fair test. According to my research, the yeast performs the best within the ranges of 4.8-5.0. However once the pH reaches 4.2, all fermentation stops, as the enzymes become denatured (Why does pH affect fermentation?, 2014).When the enzyme is denatured, the secondary and tertiary bonds are disrupted, preventing the enzyme from catalysing the reaction.
The temperature is another variable which must be controlled. The enzymes cause the chemical reaction to occur by colliding with the reactants. When the temperature is increased, the kinetic energy of the molecules increases, causing the collisions to occur more frequently. Usually, the optimal temperature for enzymes in around body temperature (37.5°C), and in yeast, the optimal temperature is 35°C. Beyond the optimal temperature, the rate of reaction decreases, as the enzymes become denatured and out of shape.
Oxygen is another variable that must be controlled. As stated before the yeast perform aerobic respiration when they have access to oxygen. This respiration does not produce ethanol, however still produces CO₂, meaning if the yeast is undergoing aerobic respiration, and not producing ethanol as the byproducts of aerobic respiration are CO₂ and H₂O. Due to this, the measurement of CO₂ will display a higher reading than the amount of CO₂ produced, therefore giving an incorrect reading of ethanol produced. (IUPUI Dep. of Biology, 2004)
The yeast used in this experiment was saccharomyces cerevisiae.
This strain of yeast is also referred to as brewer’s yeast. This yeast has a high alcohol tolerance and has the required enzymes to catalyse the reactions. (CraftBrewer, 2016)
(Concentration of Sugar)
The sugars we will be testing as stated above, are glucose, fructose, sucrose and lactose. This is a variable that affects the rate of fermentation due to enzymes. The shape of the molecules is essential to the enzymes, and the enzymes are unable to catalyse the reactions without the correct shape. The enzyme hexokinase in glycolysis can only break down glucose, therefore the other sugars must be converted to glucose, requiring more enzymes and more energy.
Glucose is the final product of photosynthesis. Its chemical formula is C₆H₁₂O₆, and it is a monosaccharide, meaning it is made up of one sugar, hence the ‘mono’. Glucose is the sugar required for glycolysis, as the enzymes that start the glycolysis process are designed to break down glucose. Therefore, no preceding enzymes are required to breakdown glucose. (Glucose, …show more content…
2016)
Fructose is a monosaccharide, which is commonly found in fruit. It shares its chemical formula with glucose (C₆H₁₂O₆), meaning that fructose is an isomer of glucose (meaning same formula but different structure). Fructose enters the fermentation at a different stage when compared to glucose. This means the enzymes are different, and this can mean the yeast can prefer fructose over glucose due to enzyme availability, but in the case of saccharomyces cerevisiae, it contains more of the enzymes required to breakdown glucose. (Dawson)
Sucrose has a chemical formula of C₁₂H₂₂O₁₁ and is a disaccharide, meaning that sucrose is two sugars bonded together. In the case of sucrose, the two sugars combined are glucose and fructose. The enzyme sucrase is responsible for the process sucrose undergoes to be broken down into glucose and fructose (Sucrase, 2016). The reaction also needs water present, to gain the two hydrogen and the oxygen molecules that are missing. (Sucrose, 2016)
The last sugar tested was lactose. Lactose is a disaccharide and shares its chemical formula with sucrose (C₁₂H₂₂O₁₁). The two sugars bonded together are glucose and galactose. The enzyme required to breakdown lactose into the monosaccharides is lactase (Lactase, 2016). However, yeast is not in the possession of lactase, giving the yeast no way to metabolise the lactose. This means the yeast cannot respire using the sugar lactose, so no ethanol or CO₂ should be produced. (Lactose, 2016)
Given that the enzymes used to catalyse reaction can only catalyse specific reactions, it can be hypothesised, that glucose will ferment the fastest, when pH, temperature, amount and type of yeast, amount of oxygen and concentration of sugar are kept the same. This is because glucose can go straight into glycolysis as it does not require any prior enzymes to break it down.
2.0 Results These graphs display the amount of CO₂ produced when yeast fermented with various sugars. CO₂ was produced in all tubes ranging from 2.4-20 mL. The conversion of CO₂ to ethanol was done via stoichiometry. This is the revised graph without the outliers from sucrose (20mL and 11.7mL) and Fructose (17.2mL).
3.0 Discussion
The purpose of this experiment was to find the best sugar for ethanol fermentation.
In this experiment, we used a variety of sugars to ferment the yeast. The results displayed that sucrose was the largest producer of CO₂, followed by fructose and glucose. Upon researching the enzymes used in the process, we determined that glucose would show more production of CO₂ than the other sugars, because the enzymes are suited to glucose. As shown above, our results refuted our hypothesis.
The results of the experiment overall did not follow a trend, as the results were separated by large margins. However, the glucose results were far closer together then the others, having a range of 2.4, whereas the range of results for fructose was 14.8 and the range for sucrose is 15.4. The reason for this is unknown, as many of the variables remained unchanged between tests. This however can be attributed to the outlier in the fifth test, where the yeast outperformed the other trials, nearly tripling them. Without this outlier, the range of fructose is reduced to 3.3 and the fructose does not produce more CO₂ than glucose. With the acceptation of glucose and lactose, the fifth test proved to be problematic. The results of the tests were overly high, indicating something had gone
wrong.
From this experiment, it can be concluded that the type of sugar used during fermentation does affect the rate at which the CO₂ is produced, due to the enzymes used to catalyse the reactions. According to our data, sucrose is the most efficient sugar for use during fermentation. This could be because once the sucrose is broken down into glucose and fructose, the two monosaccharides can begin their two separate paths of glycolysis. This could mean the rate of reaction gradually increases as the yeast breaks down the yeast into glucose and fructose, eventually overtaking glucose as the sucrose breaks down the glucose and fructose simultaneously.
Data collected from other groups corroborates with ours when the outliers are not included. Experiments found on the internet, testing the same thing, also yielded similar results to ours. However, throughout these, the results only matched up without the outliers, therefore the outliers were most probably caused by an error.
In our experiment, there was a large amount of error. This error stemmed from the measuring method. The method required the CO₂ to flow through a tube into a measuring cylinder that is submerged in water. The measuring cylinder would prevent the gas from escaping into the air, however, the CO₂ was soluble in the water, so some of the CO₂ would have been lost due to this. This could be mitigated by using a different method of measuring the ethanol produced.
If this experiment were to be repeated, extra care would be taken to ensure that fermentation began at the same time, and with the same amount of oxygen. Follow-up experiments may include testing other types of yeasts to see how fermentation rates are impacted. The results of these experiments could impact what sugars are the most efficient in alcohol fermentation, as the enzymes in each of the yeasts varies. This could determine what types of sugar and yeast combo brewers should use for the fastest production of alcohol.
In the future, another interesting experiment would be to measure the effect of time on the ethanol production. According to the theory of why the sucrose produced more ethanol, there should be a time in which the glucose produced more ethanol. The production of ethanol via sucrose should display an exponential trend, starting off slow, and gradually fermenting faster until it overtakes glucose. On the other hand, glucose should display a more linear trend, as the glycolysis process should begin instantly.
4.0 Conclusion
In conclusion, the aim of this experiment was to find the best sugar for alcohol fermentation. It was hypothesised that glucose would be the best producer of alcohol, however this was refuted by the data.
Cellular respiration is a process that living organisms undergo to create and obtain chemical energy in the form of adenosine triphosphate (ATP). The energy can be gained in two different forms of cellular …show more content…
respiration, called aerobic respiration and anaerobic respiration, also called fermentation. Glycolysis is the first stage of both anaerobic and aerobic respiration. This stage uses 10 different enzymes to turn glucose into pyruvate acid. After glycolysis, the two different forms diverge. The cell desires to preform aerobic respiration which grants the cell 36-38 ATP, however this requires oxygen. Fermentation is a process implemented by organisms to obtain ATP without the use of oxygen, however this produces only 4 ATP. When yeast is in the presence of oxygen it performs aerobic respiration, but when oxygen is absent it undergoes fermentation. In fermentation, the pyruvate acid is then converted into ethanol alcohol in two stages. In the first stage, it is converted into acetaldehyde with the release of carbon dioxide (CO2) as a byproduct, which will be used to measure the independent variable of the experiment, which is created in the second stage. This this stage the acetaldehyde is converted to ethanol. (IUPUI Dep. of Biology, 2004)
Before fermentation, glycolysis occurs. 10 enzymes are used during this process, and the initial enzyme in the process, called hexokinase, breaks down glucose and ATP into glucose-6-phosphate, ATP and hydrogen s (Spark Notes, 2016). During fermentation, 2 enzymes are used. They are pyruvate decarboxylase and alcohol dehydrogenase. Enzymes are specialized proteins used to catalyse reactions. This means the enzyme reduces the amount of energy required to perform the reaction this is called the activation energy. Enzymes do this with an active site, which is shaped to fit one specific molecule, and cannot be used to as a catalyst for any other molecules (Department of Forestry and Plant Physiology Program, University of Kentucky, Lexington, 1987). The enzymes have a primary, secondary and tertiary structures. The primary structure consists of the amino acids of the peptide bond that bonds them together. These are covalent bonds formed between C=O and N-H groups of the amino acids. The secondary structure appears as a double helix. It consists of the hydrogen bonds that form between the oxygen of the C=O in the strand and the hydrogen of the N-H group four amino acids below it in the helix.
These enzymes have acidic R groups in their amino acids, meaning the enzymes perform better in acidic conditions. This means the pH of the solution must be taken into account to ensure this is a fair test. According to my research, the yeast performs the best within the ranges of 4.8-5.0. However once the pH reaches 4.2, all fermentation stops, as the enzymes become denatured (Why does pH affect fermentation?, 2014).When the enzyme is denatured, the secondary and tertiary bonds are disrupted, preventing the enzyme from catalysing the reaction.
The temperature is another variable which must be controlled. The enzymes cause the chemical reaction to occur by colliding with the reactants. When the temperature is increased, the kinetic energy of the molecules increases, causing the collisions to occur more frequently. Usually, the optimal temperature for enzymes in around body temperature (37.5°C), and in yeast, the optimal temperature is 35°C. Beyond the optimal temperature, the rate of reaction decreases, as the enzymes become denatured and out of shape.
Oxygen is another variable that must be controlled. As stated before the yeast perform aerobic respiration when they have access to oxygen. This respiration does not produce ethanol, however still produces CO₂, meaning if the yeast is undergoing aerobic respiration, and not producing ethanol as the byproducts of aerobic respiration are CO₂ and H₂O. Due to this, the measurement of CO₂ will display a higher reading than the amount of CO₂ produced, therefore giving an incorrect reading of ethanol produced. (IUPUI Dep. of Biology, 2004)
The yeast used in this experiment was saccharomyces cerevisiae.
This strain of yeast is also referred to as brewer’s yeast. This yeast has a high alcohol tolerance and has the required enzymes to catalyse the reactions. (CraftBrewer, 2016)
(Concentration of Sugar)
The sugars we will be testing as stated above, are glucose, fructose, sucrose and lactose. This is a variable that affects the rate of fermentation due to enzymes. The shape of the molecules is essential to the enzymes, and the enzymes are unable to catalyse the reactions without the correct shape. The enzyme hexokinase in glycolysis can only break down glucose, therefore the other sugars must be converted to glucose, requiring more enzymes and more energy.
Glucose is the final product of photosynthesis. Its chemical formula is C₆H₁₂O₆, and it is a monosaccharide, meaning it is made up of one sugar, hence the ‘mono’. Glucose is the sugar required for glycolysis, as the enzymes that start the glycolysis process are designed to break down glucose. Therefore, no preceding enzymes are required to breakdown glucose. (Glucose, …show more content…
2016)
Fructose is a monosaccharide, which is commonly found in fruit. It shares its chemical formula with glucose (C₆H₁₂O₆), meaning that fructose is an isomer of glucose (meaning same formula but different structure). Fructose enters the fermentation at a different stage when compared to glucose. This means the enzymes are different, and this can mean the yeast can prefer fructose over glucose due to enzyme availability, but in the case of saccharomyces cerevisiae, it contains more of the enzymes required to breakdown glucose. (Dawson)
Sucrose has a chemical formula of C₁₂H₂₂O₁₁ and is a disaccharide, meaning that sucrose is two sugars bonded together. In the case of sucrose, the two sugars combined are glucose and fructose. The enzyme sucrase is responsible for the process sucrose undergoes to be broken down into glucose and fructose (Sucrase, 2016). The reaction also needs water present, to gain the two hydrogen and the oxygen molecules that are missing. (Sucrose, 2016)
The last sugar tested was lactose. Lactose is a disaccharide and shares its chemical formula with sucrose (C₁₂H₂₂O₁₁). The two sugars bonded together are glucose and galactose. The enzyme required to breakdown lactose into the monosaccharides is lactase (Lactase, 2016). However, yeast is not in the possession of lactase, giving the yeast no way to metabolise the lactose. This means the yeast cannot respire using the sugar lactose, so no ethanol or CO₂ should be produced. (Lactose, 2016)
Given that the enzymes used to catalyse reaction can only catalyse specific reactions, it can be hypothesised, that glucose will ferment the fastest, when pH, temperature, amount and type of yeast, amount of oxygen and concentration of sugar are kept the same. This is because glucose can go straight into glycolysis as it does not require any prior enzymes to break it down.
2.0 Results These graphs display the amount of CO₂ produced when yeast fermented with various sugars. CO₂ was produced in all tubes ranging from 2.4-20 mL. The conversion of CO₂ to ethanol was done via stoichiometry. This is the revised graph without the outliers from sucrose (20mL and 11.7mL) and Fructose (17.2mL).
3.0 Discussion
The purpose of this experiment was to find the best sugar for ethanol fermentation.
In this experiment, we used a variety of sugars to ferment the yeast. The results displayed that sucrose was the largest producer of CO₂, followed by fructose and glucose. Upon researching the enzymes used in the process, we determined that glucose would show more production of CO₂ than the other sugars, because the enzymes are suited to glucose. As shown above, our results refuted our hypothesis.
The results of the experiment overall did not follow a trend, as the results were separated by large margins. However, the glucose results were far closer together then the others, having a range of 2.4, whereas the range of results for fructose was 14.8 and the range for sucrose is 15.4. The reason for this is unknown, as many of the variables remained unchanged between tests. This however can be attributed to the outlier in the fifth test, where the yeast outperformed the other trials, nearly tripling them. Without this outlier, the range of fructose is reduced to 3.3 and the fructose does not produce more CO₂ than glucose. With the acceptation of glucose and lactose, the fifth test proved to be problematic. The results of the tests were overly high, indicating something had gone
wrong.
From this experiment, it can be concluded that the type of sugar used during fermentation does affect the rate at which the CO₂ is produced, due to the enzymes used to catalyse the reactions. According to our data, sucrose is the most efficient sugar for use during fermentation. This could be because once the sucrose is broken down into glucose and fructose, the two monosaccharides can begin their two separate paths of glycolysis. This could mean the rate of reaction gradually increases as the yeast breaks down the yeast into glucose and fructose, eventually overtaking glucose as the sucrose breaks down the glucose and fructose simultaneously.
Data collected from other groups corroborates with ours when the outliers are not included. Experiments found on the internet, testing the same thing, also yielded similar results to ours. However, throughout these, the results only matched up without the outliers, therefore the outliers were most probably caused by an error.
In our experiment, there was a large amount of error. This error stemmed from the measuring method. The method required the CO₂ to flow through a tube into a measuring cylinder that is submerged in water. The measuring cylinder would prevent the gas from escaping into the air, however, the CO₂ was soluble in the water, so some of the CO₂ would have been lost due to this. This could be mitigated by using a different method of measuring the ethanol produced.
If this experiment were to be repeated, extra care would be taken to ensure that fermentation began at the same time, and with the same amount of oxygen. Follow-up experiments may include testing other types of yeasts to see how fermentation rates are impacted. The results of these experiments could impact what sugars are the most efficient in alcohol fermentation, as the enzymes in each of the yeasts varies. This could determine what types of sugar and yeast combo brewers should use for the fastest production of alcohol.
In the future, another interesting experiment would be to measure the effect of time on the ethanol production. According to the theory of why the sucrose produced more ethanol, there should be a time in which the glucose produced more ethanol. The production of ethanol via sucrose should display an exponential trend, starting off slow, and gradually fermenting faster until it overtakes glucose. On the other hand, glucose should display a more linear trend, as the glycolysis process should begin instantly.
4.0 Conclusion
In conclusion, the aim of this experiment was to find the best sugar for alcohol fermentation. It was hypothesised that glucose would be the best producer of alcohol, however this was refuted by the data.