Effect Of Type Of Sugar On Rate Of Cellular Respiration In Yeast

Being passionate about cooking and especially baking, I know the process of using yeast mixed with flour and sugar to make breads and cakes. Yeast are used in the process as they ferment complex carbohydrate units and release carbon dioxide which causes the bread to rise up. This process is aerobic in nature as oxygen is utilized in the process where yeast undergoes cellular respiration. During such process, yeast releases carbon dioxide and energy. The type of sugar used in such process plays a major role as the type of sugar is not same everywhere. From the industrial aspect, it is that the process is fast enough. The purpose of this investigation is to understand whether the type of sugar used has any effect on the rate of cellular respiration or not. The rate of such process can be monitored by quantitative measurement of the carbon dioxide evolved during the process. Thus, I decided to narrow down my Internal Assessment in Biology on the research question phrased below-

Does the rate of cellular respiration (measured in terms of amount of carbon dioxide evolved per min over an interval of 30 minutes) in yeast (Saccharomyces cerevisiae) depends on the type of sugar (sucrose, fructose and glucose) used?

Yeasts are unicellular globular shaped fungi. They have the ability to produce energy on fermentation of carbohydrates through respiration. This can happen both is presence and absence of oxygen. The respiration that happens in presence of oxygen is aerobic respiration and the chemical equation is for that is as follows:

Glucose + Oxygen\(\rightarrow\) Carbon dioxide + Water + ATP (energy)

The same process is recognized as an anaerobic respiration when it happens in absence of oxygen and the equation is as follows:

Glucose\(\rightarrow\) Ethanol + Carbon dioxide + ATP (energy)

It must be noted that carbon dioxide is evolved as a by product in both aerobic and anaerobic respiration. Anaerobic respiration is also known as fermentation. As alcohol (ethanol) are produced during fermentation, this is also known as alcoholic fermentation. In both cases, energy is produced as ATP molecules. The amount of energy produced during aerobic respiration is much higher than that in anaerobic respiration.

The current investigation is focused on aerobic respiration which is a cellular process happening in yeast.

Aerobic respiration in yeast follows a catabolic pathway comprising mainly of four different steps- Glycolysis, Link Reaction, Kreb’s cycle and chemiosmosis. The release of carbon dioxide from the cell wall happens during the last stage which is chemiosmosis. Due to combustion process happening inside the cell, the osmotic pressure is higher inside the cell which causes the carbon dioxide to be released out of the cell. The release of carbon dioxide from the cell wall during cellular respiration results in the formation of foam. Hence, the rate of respiration can be monitored by both measuring the rate at which carbon dioxide is evolved as well as the amount of foam produced.

Yeast secretes a lot of enzyme during each and every step of the aerobic respiration. As enzymes gets denatured (loses their shape and cannot bind to the substrate) at high temperature, controlling temperature during this process is essential. The process is carried out at 40.0oC as that has been reported to be the optimum temperature of fermentation.

The amount of foam produced can be measured in terms of amount of Carbon dioxide at regular intervals of time and the values can be plotted against the time. The rate of the reaction can be determined from the gradient of such plots.

A literature review of a research article on the title¹ - The effect of different sugars in the medium on carbon dioxide production in Saccharomyces cerevisiae by Jason Angustia, Maggie Chan, Deirdre Dinneen, Shamim Hortamani, Diane Mutabaruka reveals that the rate of cellular respiration is higher for glucose and fructose in comparison to sucrose. The level of CO₂ produced was recorded as a function of time for four different types of sugars – glucose, maltose, fructose and sucrose. The image below² is a snap shot of the data table of that research article in support of the statement written above.

There is no correlation between the type of sugar used and the rate of cellular respiration.

There is a correlation between the type of sugar used and the rate of cellular respiration.

• Yeast
• Glucose – 10.00 g
• Sucrsoe – 10.00 g
• Fructose – 10.00 g
• Distilled water – 1000cc

• Yeast is not a harmful organism but inhalation or direct ingestion is not recommended. Thus a physical barrier with the microorganism is essential to avoid any sort of cross contamination. Protective clothings like safety gloves, lab coats were used.
• None of the materials used were ingested or exposed to skin. Eatables were not allowed inside the laboratory as the microorganism used might infect them.

The methodology adopted or the issue at which the investigation is focused on does not have any ethical issues.

18.00 ± 0.01 g (0.1 moles) of glucose was weighed on a watch glass using a digital mass balance. The weighed solid was transferred to a neat and dry 100 cc volumetric flask and dissolved in 100 cc distilled water.

Similarly, aqueous solutions of sucrose and fructose were prepared by dissolving 34.2 g of sucrose and 18.0 g of fructose in 100 cc of distilled water.

• A 250 cc glass beaker was taken and filled with 50 cc of the glucose solution.
• 5.00 ± 0.01 g of yeast was weighed on a watch glass using a digital mass balance and added to it.
• The stop-watch was started.
• The amount of CO₂ produced was then measured after 5 minutes using a CO₂ gas sensor.
• The gas sensor was calibrated before use.
• The measurement of CO₂ produced was continued till 30 minutes at an interval of 5 minutes.
• Steps 1-5 were repeated for four more times to collect data in five sets.
• Steps 1-6 were repeated for other two solutions – sucrose and fructose.

•  The sugar solutions used were transparent and clear.
• Addition of yeast to the sugar solution turned the solution turbid. 
• With the progress of time, the solution turned more turbid and more foam were produced.

Sample calculation

Average amount of CO₂ evolved in ppm ( for 300.00 s) =\(\frac{300+310+300+320+330}{5}\)= 312.00

Standard deviation = \(\frac{(300-312)^2+(310-312)^2+(300-312)^2+(320-312)^2+(330-312)^2}{5}\) = 13.04

The above graph is a scattered plot of amount of CO₂ evolved in ppm against time in seconds. The error bars are plotted using MS-Excel. A linear trend line has been derived using MS-Excel. The equation follows the format y=mx + c ; where y represents the amount of CO₂ evolved in ppm and x represents the time in seconds.

The gradient of the equation is represented as m and it represents the rate of the reaction in ppm/min. 

Equation of linear trend line: y = 0.149 x + 256.61

Rate of fermentation of glucose = 0.149 ppm/min

It means that during the fermentation of glucose, 0.149 ppm of CO₂ is evolved per minute on an average.

The above graph is a scattered plot of amount of CO₂ evolved in ppm against time in seconds. The error bars are plotted using MS-Excel. A linear trend line has been derived using MS-Excel. The equation follows the format y=mx + c ; where y represents the amount of CO₂ evolved in ppm and x represents the time in seconds.

The gradient of the equation is represented as m and it represents the rate of the reaction in ppm/min.

Equation of linear trend line: y = 0.073 x + 291.27

Rate of fermentation of fructose = 0.073 ppm/min

It means that during the fermentation of fructose, 0.073 ppm of CO₂ is evolved per minute on an average.

The above graph is a scattered plot of amount of CO₂ evolved in ppm against time in seconds. The error bars are plotted using MS-Excel. A linear trend line has been derived using MS-Excel. The equation follows the format y=mx + c ; where y represents the amount of CO₂ evolved in ppm and x represents the time in seconds.

The gradient of the equation is represented as m and it represents the rate of the reaction in ppm/min.

Equation of linear trend line: y = 0.034 x + 294.72

Rate of fermentation of fructose = 0.034 ppm/min

It means that during the fermentation of fructose, 0.034 ppm of CO₂ is evolved per minute on an average.

Graph-4 is a bar graph to compare the rates of cellular respiration in yeast for different types of sugar. The height of the bars represents the rates of cellular respiration as it is plotted along the y axes while the type of sugar is plotted along the x axes. As it is clearly visible in the graph, the rate of cellular respiration is maximum for glucose – 0.149 ppm/.min and minimum for sucrose (0.034 ppm/min).

Cellular respiration is a biochemical process where glucose undergoes combustion to produce carbon dioxide and release energy in the form of ATP molecules along with formation of H2O.

Glucose + Oxygen \(\rightarrow\) Carbon dioxide + Water + ATP

Experimental studies has revealed³ that the bottleneck of this process is related to uptake of sugar by the microorganism and yeast can consume the nutrient only in the form of glucose.

Glucose is a simple carbohydrate or a monosaccharide to be specific. Any other carbohydrate used has to be first hydrolyzed to form glucose before cellular respiration occurs. Fructose is also a monosaccharide. It can be converted to glucose by the enzyme isomerase as glucose and fructose are isomers of each other. Thus, in case of glucose, the substrate is directly available while in case of fructose, first the raw material has to undergo isomerization to glucose and then the reaction begins. This clearly explains why the rate of cellular respiration is faster with glucose and slower with fructose.

Sucrose is a disaccharide. It is formed by joining two simple sugars – glucose and fructose through glycosidic linkages. Hence, first sucrose has to undergo hydrolysis to form glucose and fructose and then the cellular respiration begins as the substrate for this process is glucose and not fructose. Thus, during the case of sucrose, there are two steps that must happen before the cellular respiration begins- hydrolysis of sucrose to glucose and fructose and then isomerization of fructose to glucose. This delays the process of cellular respiration and thus the rate is lowest in case of sucrose.

Thus it is clear that the rate of cellular respiration is faster with mono-saccharides –glucose and fructose than disaccharides –sucrose.

The basic aim of the investigation is to compare the rates of cellular respiration for different type of sugar units. The sugar units chosen for this investigation are glucose, fructose and sucrose. Glucose and fructose are mono- saccharides while sucrose is a disaccharide. An independent T test will be performed with glucose (a mono saccharide ) and sucrose (a disaccharide). The purpose of the T test is to understand if the type of sugar – monosaccharide or disaccharide do have an effect on the rate of cellular respiration or not.

Null hypothesis

Rate of cellular respiration in yeast has no correlation with the type of sugar used-monosaccharide or disaccharide.

Alternate hypothesis

There is a significant statistical difference between the rates of cellular respiration between the two different types of sugar units used-monosaccharides or disaccharides.

Degrees of freedom = (6 + 6) – 1 = 11

Critical value of t = 2.201

Calculated t value = \(\frac{413.13-330.50}{\sqrt({}\frac{(84.20)^2}{6}+\frac{(19.18)^2}{6}}\)= 2.343

Thus it is observed that the calculated value of t (2.343) is greater than the critical value of t (2.201). Hence, the null hypothesis is rejected and the alternate hypothesis is accepted.

Hence, we can conclude that the rate of cellular respiration in yeast depends on the type of sugar unit used.

The basic aim of the investigation was to answer the research question-

Does the rate of cellular respiration (measured in terms of amount of carbon dioxide evolved per min over an interval of 30 minutes) in yeast (Saccharomyces cerevisiae) depends on the type of sugar (sucrose, fructose and glucose) used?

• As indicated in Graph-4, the rate of cellular respiration in yeast depends on the type of sugar used. The rate of cellular respiration is found to be maximum for glucose (0.149 ppm/min) and least for sucrose (0.034 ppm/min). The rate for fructose is intermediate lower than glucose and higher than sucrose. In general, it can be claimed that the rate of cellular respiration is higher for monosaccharides (glucose, fructose) than disaccharides (sucrose).
• The qualitative observations noted are also in support of the conclusion made. It was observed that the rate of formation of foam was maximum for glucose and minimum for sucrose.
• To investigate further the dependence of rate of cellular respiration on the type of sugar, an independent T test was conducted which indicates that there is a significant difference between the rates of cellular respiration in monosaccharides and disaccharides. Thus, the null hypothesis has been rejected and the alternate hypothesis has been accepted.
• The magnitude of correlation coefficient (R² ) has been determined in Graph-1, Graph-2 and Graph-3 where the amount of CO₂ evolved in ppm has been plotted as a function of time. The values of R² are 0.9874 (for glucose), 0.9983 (for fructose) and 0.9944 (for sucrose). These values confirms that there is a strong positive correlation between the amount of CO₂ evolved (an indicator of rate of cellular respiration) and time. It means that with the progress of time, the cellular respiration becomes faster.

• The values of standard deviation has been calculated in each data tables and the values indicates a close agreement between all the trial values collected which means that there is a huge precision in the data collection.
• To support the claims made, the processed data was used in inferential statistics. An independent T test has been conducted to evaluate the hypothesis instead of simply relying on data processing.
• The procedure adopted does not require any complex setting and can be easily performed in a school laboratory set up.
• The focus of the investigation conducted has an industrial point of view as the choice of right sugar in making of breads or alcohol is important to fasten the process.

There are multiple sources of random error in the experiment. These includes – uncertainty of apparatus used, lose of mass while preparing the solutions as the solid may not have been transferred completely. Adequate measures were taken to minimize the random error incurred because of these. Precise apparatus was used wherever possible like using a volumetric flask instead of a glass beaker to prepare the solutions. The solid was transferred using a funnel instead of adding it simply to the volumetric flask.

Although a CO₂ gas sensor has been used to measure the CO₂ levels in ppm, it must be noted that here sensors cannot be used to measure the amount of dissolved CO₂. Some of the CO₂ produced out of cellular respiration might get dissolved in the water and would thus not get detected or measured by the sensor. Moreover, the sensor will also take into account the level of CO₂ in the atmosphere. To correct this, the amount of CO₂ in the reaction site must be determined using the sensor prior to the investigation and this value must be subtracted from all the readings taken so that we measure only the CO₂ produced out of cellular respiration.

Two electronic measuring devices have been used in the investigation- digital mass balance and the gas sensor. Both of these instruments can have zero error. To compensate this, the instruments must be calibrated before use using standard methods. If we observe Graph-1, Graph-2 and Graph-3, the linear trend line in anyone of them do not pass through the origin which confirms that this systematic error has interfered with the data collected and has thus reduced the accuracy of the results concluded.

I would like to repeat the same investigation by changing two other conditions – temperature and amount of yeast. I would like to perform the experiment using a water bath and vary the temperature. At each temperature, I would measure the amount of CO₂ evolved in ppm using the gas sensor at regular intervals of time. Then, the amount of CO₂ evolved can be plotted against time to find the rate from the gradient of the curve. Thus, we can determine the rate of the process at various levels of temperature. This can enable us to understand the correlation between temperature and the rate of cellular respiration in yeast.

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