Effect of Sugars on Rate of Respiration of Baker's Yeast, Lecture notes of Biology

Download Effect of Sugars on Rate of Respiration of Baker's Yeast and more Lecture notes Biology in PDF only on Docsity! Effect of Sugars on Rate of Respiration of Baker’s Yeast Biology HL Internal Assessment November 5, 2018 1 Design Research Question: ​What is the effect of different types of sugars (maltose, sucrose, glucose, fructose) on the rate of anaerobic respiration of ​Saccharomyces cerevisiae​ (Baker’s yeast) obtained by the amount of carbon dioxide (ppm) produced? Personal Engagement My interest in this topic was sparked when I helped my mother bake ​naan​, a type of Indian flatbread. I was fascinated to see how the yeast helped the ​naan​ to rise and was curious as to the scientific explanation behind it. When I learnt more about respiration and its applicability to real-life (for breadmaking and alcoholic drinks), I was curious about how different sugars may affect how fast yeast respired. Background Research Cellular respiration is the conversion of carbohydrates into usable energy, in the form of ATP, which is used for metabolism, cell function and maintenance, and growth (Perry & Burggren, 2007). Respiration is important to study because it is universal; almost every organism respires (Perry & Burggren, 2007). The formula for cellular respiration is: C​6​H​12​O​6​ (glucose) + 6O​2​ → 6CO​2​ + 6H​2​O + ATP (energy) This lab, however, will not be focusing on aerobic respiration which requires oxygen. The lab investigates the rate of respiration in ​Saccharomyces Cerevisiae​, commonly known as Baker’s yeast. When it has run out of oxygen, yeast uses anaerobic respiration to break down glucose molecules and convert them to ATP. After, it starts producing ethanol--this process is called fermentation. It is important to note that glucose isn’t yeast’s only source of energy, but the preferred source (Rodrigues, Ludoviko, & ​Leão, 2006). ​The first step of anaerobic respiration is glycolysis. In glycolysis, the starting glucose molecule is rearranged into fructose-6-phosphate by enzymes, where two phosphate groups attach to it, making it unstable and causing the molecule to split (Bear & Rintoul, 2013). This uses 2 ATP molecules. The resulting 3-carbon sugars are converted to pyruvates through several reactions, each 3-carbon sugar producing 2 ATP and 1 NADH (electron carrier) molecule (Bear & Rintoul, 2013). Thus, glycolysis results in the net production of 2 ATP and 2 molecules of NADH. The second step of anaerobic respiration is fermentation. The purpose of fermentation is to oxidise NADH so it can be reused as an electron carrier; fermentation produces ethanol (Bear & Rintoul, 2013). The equation for fermentation is: C​6​H​12​O​6​ (glucose) → 2CH​3​CH​2​OH (ethanol) + 2CO​2 The metabolism of disaccharides is a bit different from that of monosaccharides. In yeast, an enzyme called invertase hydrolyses sucrose into fructose and glucose ​outside​ of the cell (Godoy et al., 2014). Maltose is transported ​into​ the cell (via active transport) and metabolised by an enzyme called glucosidases (Godoy et al., 2014). Then the monosaccharides go through glycolysis. CO​2​ is one of the products of respiration. Therefore, the volume of CO​2​ produced will be measured to calculate the rate of respiration. Yeast requires five minutes in warm water to be activated to carry out respiration (Jaworski). This step will thus be added in the method. Aim The yeast ​S. cerevisiae ​was used for the experiment because it grows quickly and efficiently in anaerobic conditions (Rodrigues, Ludoviko, & ​Leão, 2006).​ At first glance, the choice of sugars may seem random. Glucose and fructose are monosaccharides whereas maltose and sucrose are disaccharides. However, the aim of this lab is to investigate whether sugars are 4 a. Put 10g of each sugar in a separate beaker using a weighing scale to measure the exact amount. b. Pour 100 ml of distilled water into each of the beakers using a graduated cylinder to measure the water. c. Stir the solutions until the sugar has dissolved completely. 4. Pour 5mL of the yeast solution into a test tube and put it in the water bath for five minutes to activate the yeast. 5. Pour the yeast solution (5mL) and one of the sugar solutions (100mL) into the carbon dioxide probe bottle and cap it (with the probe). Make sure to start the timer. 6. Record the amount of CO​2​ produced in 1-minute intervals for ten minutes. Take qualitative observations. 7. Repeat steps 5-6 with the all the sugars (maltose, sucrose, glucose and fructose) and no sugar added. Do five trials for each sugar. Note: ​If the sugar solution or yeast solution are all used up, repeat Steps 2 and 3 to make more as needed keeping the concentration the same. Table 4. ​Safety Safety Categories Description How To Avoid Physical 1. Glassware can break and cause injuries. 2. Solutions may spill onto clothes or into eyes. 1. Handle glassware carefully. If it breaks, call an adult immediately. 2. Wear lab coat and goggles. Ethical 1. Wasting sugar by using it for a lab and then throwing it away may be seen as unethical. 1. Use the minimum amount of sugar for the experiment. Environmental 1. Dumping the yeast solution in the sink will most likely go down the drain and end up in the river and pollute it. 1. Dispose of yeast solution in a separate container. 5 Data Processing Table 5. ​Raw Data Time (min) 0 1 2 3 4 5 6 7 8 9 10 Control (no sugar) -- Volume of CO​2​ (ppm +/- 10%) Trial 1 0 0 0 0 0 0 0 0 0 0 0 Trial 2 0 0 0 0 0 0 0 0 0 0 0 Trial 3 0 0 0 0 0 0 0 0 0 0 0 Trial 4 0 0 0 0 0 0 0 0 0 0 0 Trial 5 0 0 0 0 0 0 0 0 0 0 0 Maltose -- Volume of CO​2​ (ppm +/- 10%) Trial 1 0 16 44 60 110 119 132 144 144 166 169 Trial 2 0 109 178 203 206 222 272 306 337 362 384 Trial 3 0 162 212 266 331 365 415 440 478 484 512 Trial 4 0 25 34 69 75 75 81 112 125 131 162 Trial 5 0 243 296 334 390 393 424 455 480 496 502 Sucrose -- Volume of CO​2​ (ppm +/- 10%) Trial 1 0 50 71 100 109 112 131 137 140 146 156 Trial 2 0 3 4 10 23 29 49 51 57 62 64 Trial 3 0 112 172 216 244 272 287 297 315 328 331 Trial 4 0 32 78 113 141 169 191 206 228 235 250 Trial 5 0 13 101 141 176 191 223 251 272 294 310 Glucose -- Volume of CO​2​ (ppm +/- 10%) Trial 1 0 130 146 180 186 196 202 269 387 405 492 Trial 2 0 200 259 309 350 365 378 400 419 428 440 Trial 3 0 191 316 384 425 444 459 469 487 500 512 Trial 4 0 57 78 100 106 122 135 153 163 181 191 6 Trial 5 0 94 150 188 209 231 244 287 303 325 341 Fructose -- Volume of CO​2​ (ppm +/- 10%) Trial 1 0 56 79 98 109 118 149 171 203 214 234 Trial 2 0 59 65 68 75 78 84 84 87 93 100 Trial 3 0 4 35 57 66 78 91 100 113 119 125 Trial 4 0 57 78 100 106 122 135 153 163 181 191 Trial 5 0 94 150 188 209 231 244 287 303 325 341 To obtain accurate data, at minute 0, 0 ppm of CO​2​ was assumed. The rest of the values were subtracted from the starting measurement. For example, if there was 210 ppm at 0 minutes, and 243 ppm at 1 minute, the measurement for 1 minute would be 243-210 = 33 ppm. Table 6. ​Qualitative Observations Sugar Photograph Observations Control ● There is no reaction at all. Maltose ● The solution is much hazier than that of glucose. ● Beaded particles of what I think is maltose appeared on the sides of the bottle. Sucrose ● The solution is lighter in colour than maltose and glucose. ● A lot of the sucrose particles have sank to the bottom even though in the sugar solution, the sucrose had been dissolved. 9 A bar graph was chosen to represent the mean average rate of reaction of each sugar mixture because it clearly shows the difference in rate. The data for each sugar is also independent. The error bars were created by finding the standard deviation of the average rates of reactions for all the trials of each sugar. Glucose seems to have the fastest mean average rate. However, the rates of other sugars are pretty close in value. The error bars are overlapping which suggests that the difference in rates isn’t significantly different. Discussion The experiment aimed to investigate the effect of different types of sugars (maltose, sucrose, glucose, fructose) on the rate of anaerobic respiration of Saccharomyces cerevisiae (Baker’s yeast). The alternative hypothesis argued that fructose would have the fastest rate of respiration followed by glucose, sucrose, and maltose because fructose didn’t have to be converted for respiration to occur, and monosaccharides would ferment faster than disaccharides. The findings (see ​Table 7​) showed that glucose had the highest rate of reaction, 39.5 ppm min​-1​. This was followed by maltose (34.6 ppm min​-1​), sucrose (22.2 ppm min​-1​) and fructose (19.8 ppm min​-1​). The controlled solution with no sugar produced no CO​2​. The control was used to ensure that fermentation by yeast only occurred when sugar was present. Since no CO​2​ was produced, it is safe to assume that this is indeed the case. The qualitative observations, to a certain extent, supports the quantitative data. After fermentation, the glucose solution was the most odorous and the solution seemed to get paler almost immediately after yeast was added. The fructose solution was the most difficult to dissolve in the water. One trend in the raw data (​Table 4​) is that the reactions for most trials of maltose, sucrose and fructose started fast and then gradually slowed down. For glucose, however, the rate of reaction starts fast, starts slowing down after around five minutes, and speeds up again. This may be a possible evaluation point. However, it also supports that ​S. Cerevisiae​ is more efficient in fermenting glucose. The results of this experiment are in accordance with Hopkins (1928) who did a study investigating the difference in fermentation rates of fructose and glucose by ​S. Cerevisiae​. and found that glucose fermented faster than fructose. Hopkins (1928) also found that glucose doesn’t convert into fructose while being fermented by ​S. Cerevisiae. ​This is important because it counters my alternative hypothesis. However, Hopkins (1928) also pointed out that other species of yeast such as Sauterne yeasts ferment fructose faster than glucose. Therefore, the high fermentation rate of glucose is attributed to enzymes of ​S. Cerevisiae ​being more efficient. This brings up an evaluation point of this experiment which is that there are many factors which show the rate of fermentation, not just the production of CO​2​. The enzymes used, as pointed out, are a better indication of fermentation rate. This experiment is reductionist in that sense. The rate of fermentation of sucrose was slower than maltose contrary to the alternative hypothesis. Based on the Hopkins (1928) study, this makes sense because maltose is made of two glucose molecules whereas sucrose--of fructose and glucose. It has been shown that glucose ferments much faster than fructose as stated above. Furthermore, according to Batista et al., the metabolic pathway (of fermentation) of sucrose is actually inefficient because it is metabolised outside the cell which is a bit counter-intuitive because monosaccharides would be easier to transport into the cell than disaccharides. Although the fermentation rates of the sugars were different, it is important to know whether there is a statistically significant difference. Unfortunately, an ANOVA test cannot be done 10 because the data was continuous. Furthermore, the mean average rates of reaction couldn’t be used because they were enough data points. Therefore, the study must conclude that there is a difference between fermentation rates in different sugars by ​S. Cerevisiae​ but it isn’t clear whether the difference is statistically significant or not. Relating this back to what inspired me to carry out this experiment, my mother uses sucrose, refined white sugar (“Types of Carbohydrates”), to make ​naan​. My mother and I take two hours to make ​naan​. However, this experiment suggests that using glucose would be better because the rate of respiration is faster. Thus, we would take a lesser amount of time to make ​naan​. Evaluation Although the data shows that there is a difference in fermentation rates of sugars, there are several improvements that can be made to this experiment. First is the need for more trials. There were twenty-five trials in total resulting in twenty-four degrees of freedom. More trials will lead to better statistical results. Second, the length taken for fermentation was only ten minutes and as can be seen from ​Table 4​, a plateau wasn’t reached which suggests that complete fermentation hadn’t occurred. This is a concern because the data doesn’t represent the full reaction that takes place and the average rate of fermentation isn’t accurate. An improvement would be to allow the yeast to respire for a longer period of time. Another improvement concerning time is the increments in which data was collected. Shorter increments would have led to better data because the trends and patterns would have been easier to see. There is also a question of whether the range of independent variables was sufficient or not. The aim of the experiment was to compare the rate of metabolism of disaccharides to that of monosaccharides. Considering this aim, the range of independent variables was sufficient because glucose and fructose are monosaccharides whereas maltose and sucrose are disaccharides made up of glucose, and glucose and fructose respectively. Thus, monosaccharides are effectively being compared to disaccharides. Below is a table of more errors and improvements. A wider variety of sugars could also have been tested to determine the best sugar for respiration by Baker’s yeast. Table 9. ​Sources of Errors Source of error Significance Improvement There were some clusters of yeast at the bottom of the CO​2 probe’s bottle. Moderate: ​The yeast may have needed more time to be activated. It was only kept in the water bath for five minutes prior to each trial. No measure was taken of whether the yeast was fully activated or not. This would have affected the rate of fermentation. Put the yeast in the water bath for at least ten minutes. The data wasn’t collected on the same day at the same time. Low:​ The surrounding environment, although done in the same lab, would have All data should be collected on the same day under highly controlled conditions. 11 different conditions such as temperature of the room, humidity etc. This may have affected the fermentation of the yeast. The equipment used all had large uncertainties. For instance, the CO​2​ probe had an uncertainty of 10%. High: ​The data obtained isn’t as accurate as it could have been. Better and more accurate instruments with lower uncertainties should be used. There was a short gap of time (of about two or three seconds) after the yeast and sugar solution had been poured into the CO​2 sensor’s bottle and the probe’s recording had started. Low:​ The yeast may have started fermenting the sugar immediately after being poured into the sugar solution. There would have been a delay in the data collected. Thus, the data collected isn’t as accurate as it could have been. If the same equipment (Vernier’s CO​2​ probe is being used), it is difficult to eliminate the problem. However, the delay can become a controlled variable instead. CO​2​ production can be recorded after exactly five seconds so that it’s the same for all trials. The standard deviation was also calculated for all sugars. With the exception of the controlled, which had a standard deviation of 0, the data deviated a lot from the mean average. This indicates that the results were not precise nor accurate. The standard deviations ranged from 95.8 to 172.1. There was indeed a lot of variation in the data. This also affected the mean average rate of fermentation to become very skewed. By replicating this experiment and following the improvements listed above, such a high standard deviation can be avoided. Next testable question: ​What is the effect of different types of sugars (maltose, sucrose, glucose, fructose) on the rate of reaction by zymase? According to Alba-Lois and Segal-Kischinevzky, zymase is an enzyme used by yeast to ferment sugars. It was mentioned that a limitation of this experiment was it used too broad of an approach--the production of CO​2​--to measure fermentation rate. By focusing on the work of a specific enzyme in yeast, we can get a better understanding of which sugars are fermented faster.