Yeast Investigation

Tim Borgas IB Biology

Yeast Investigation

Introduction:

Saccharomyces cerevisiae is a species of yeast most commonly used in baking and brewing. Like Escherichia coli is the model organism for Prokaryotes, S. cerevisiae is one of the most common model organisms for Eukaryotes (figure 1). It is the microorganism behind the most common type of fermentation. S. cerevisiae cells are mostly round with a diameter of 5–10 micrometers. It reproduces by a division process known as budding. Many proteins important in human biology were first discovered by studying their equivalent in yeast; these include cell cycle proteins, signaling proteins, and protein-processing enzymes. (Figure 1)

When yeast respires, it uses hexose sugars such as glucose and fructose or it uses disaccharides such as sucrose and maltose as a source of energy. This ingredient in conjunction with oxygen results in aerobic respiration with the products of carbon dioxide and water (figure 2). If there is no oxygen present, alcoholic fermentation takes place and the energy source is turned into ethanol and carbon dioxide (figure 2). In this investigation, sucrose will be used as an energy source, and the volume of carbon dioxide produced by constant volumes of yeast in different concentrations of one molar sucrose solution will be investigated. Most probably, the most carbon dioxide will be produced in the higher concentrations of sucrose as there is more substrate for the yeast to break down.

(Figure 2)

Research Question:

What is the effect on the volume of carbon dioxide produced, by 8 ml of (yeast) respiring with sucrose solution, when the sucrose solution varies in concentration such that the yeast respires with 7 ml of 60, 80, and 100% one molar sucrose solution?

Variables:

Independent: Concentration of sucrose solution. This will be varied by the following method:

Add 100 ml of distilled water into a conical flask.
Slowly dissolve 34.23 grams of sucrose in it to make the 1 molar solution.

Dependent: Volume of CO2 produced over 7 hours. This will be the product of precisely 8ml of yeast solution respiring aerobically with oxygen and 7ml of different concentrations of a one molar sucrose solution. It will be measured by the displacement method: an up-side-down measuring cylinder with a measuring capacity of 100ml filled with tap water and placed in a large water filled beaker will be filled with the carbon dioxide from the side arm of the side arm test tube slowly displacing the tap water inside. This enables the direct reading of the exact volume of carbon dioxide produced by the yeast in the sucrose solution.

Controlled:

Temperature: As respiration relies on enzymatic processes, and enzymes operate differently at different temperatures, temperature will have to remain constant in order to gain constant results. The experiment will remain in the same room, taking room temperature as the constant for all trials across the whole experiment.
pH: Again, as respiration relies on enzymatic processes, and enzymes operate differently at different pH values, pH will have to remain constant in order to gain constant results. All solutions in the experiment will be water based, therefore neutral, in order to keep everything at the same pH levels.

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Controlled:

Temperature: As respiration relies on enzymatic processes, and enzymes operate differently at different temperatures, temperature will have to remain constant in order to gain constant results. The experiment will remain in the same room, taking room temperature as the constant for all trials across the whole experiment.
pH: Again, as respiration relies on enzymatic processes, and enzymes operate differently at different pH values, pH will have to remain constant in order to gain constant results. All solutions in the experiment will be water based, therefore neutral, in order to keep everything at the same pH levels.
Pressure: As the method used to measure carbon dioxide is the displacement method, the pressure will have to remain constant in order to gain equal results. This will be achieved, by using the same water (tap water) and keeping the experiment in constant temperature conditions.
Equipment: The equipment use will have to remain the same in order to be able to compare the results. To ensure this, the same model equipment (measuring cylinders, beakers, side arm test tubes, rubber stoppers, conical flask, test tube rack, clamp stand with clamps) will be used throughout the experiment. Further, yeast and sucrose from the individual same producers will be used in order to ensure constant results.

Uncontrolled:

Quality of Yeast: The quality of the yeast in the yeast solution cannot be controlled as it is bought from mass producers. In order to minimize this disadvantage, the yeast used in the experiment will all come from the same producer.
Purity of Sucrose: Likewise, the purity of the sucrose is not guaranteed as it is bought from a mass producer. In order to minimize this disadvantage, the sucrose used will all come from the same producer.

Apparatus:

Three 100ml measuring cylinders
Three 500ml beakers
Two 10ml measuring cylinders
Three side arm test tubes with glass and rubber extensions attached
Three rubber stoppers to fit the side arm test tubes.
One conical flask
One test tube rack
One clamp stand with clamps
Unspecified volume of tap water
150ml of distilled water
35g of pure sucrose
50ml of yeast/water mixture with yeast of the species Saccharomyces cerevisiae
One stopwatch or timer

Method:

Set up the apparatus as shown below, leaving the stopper off the still empty side arm test tube.

Prepare the 1 molar sucrose solution by the following method:

Add 100 ml of distilled water into a conical flask.
Slowly dissolve 34.23 grams of sucrose in it to make the 1 molar solution.

Prepare the individual concentrations of the one molar sucrose solution by the following method:

Add precisely 7ml of one of the concentrations of one molar sucrose solution to the side arm test tube.

Add precisely 8ml of yeast solution to the side arm test tube and close it using a rubber stopper. At the same time, start the timer.

Record the results of how much carbon dioxide has been displaced in the measuring cylinder at regular time intervals (preferably in hours).

Repeat steps 4 to 6 with the other two concentrations of the one molar sucrose solution.

Repeat steps 3 to 7 as often as possible to gain multiple trials.

Table, to show the volume of CO2 produced by 8 ml of yeast in 7 ml of given concentrations of one molar sucrose solution over 7 hours:

The Results show that the volume of carbon dioxide produced is generally increased with the concentration of the one molar sucrose solution. It also became apparent that, during the experiment, more carbon dioxide was produced when the reacting mixture in the side arm test tube was shaken. The capacity limit of the 100ml measuring cylinder was also reached after the seven hours of respiring. Further, the distinction between the carbon dioxide produced by aerobic respiration and that produced by anaerobic respiration was impossible.

Taking the Mean:

To be able to graph the results, their mean must first be determined across the trials

The Mean of the results at 60, 80, and 100% sucrose solution can be calculated using the following formula: (where: T1= Trial 1 in ml; T2= Trial 2 in ml; and A= Average in ml)

e.g. from data:

(Where: T1= 99 ml; T2= 102 ml; and A= Average in ml)

Uncertainty:

The uncertainty of this average is given by (± 0.05) + (± 0.05) = (± 0.1 ml)

Table, to show the average volume of CO2 produced by 8 ml of yeast in 7 ml of given concentrations of one molar sucrose solution over 7 hours:

Table, to show the increase of CO2 production with concentration of 1 molar sucrose solution over seven hours

Graph, to show the volume of CO2 produced by 8 ml of yeast in 7 ml of given concentrations of one molar sucrose solution over 7 hours:

Green = 100% of 1 molar sucrose solution, Red = 80% of 1 molar sucrose solution, Blue = 60% of 1 molar sucrose solution

Graph, to show the increase of CO2 production with concentration of 1 molar sucrose solution over seven hours

Green = Average, Red = Trial 2, Blue = Trial 1

Rate of carbon dioxide production:

To be able to calculate the rate at which the yeast cells produced the carbon dioxide in ml per minute, the average results must be divided by the number of minutes at which their reading was taken.

The rate at which the yeast cells produced the carbon dioxide in ml per minute can be calculated using the following formula: (where: Ar = Average result in ml; t = time at which the result was collected in minutes; and R= Rate of CO2 production in ml/min)

e.g. from data:

(Where: Ar = 100.5 ml; t = 420 min; and R= Rate of CO2 production in ml/min)

Uncertainty:

The uncertainty of this average is given by ±0.100 ml/min

Table, to show the average volume of CO2 produced by 8 ml of yeast in 7 ml of given concentrations of one molar sucrose solution over 420 minutes:

Graph, to show the rate of CO2 production after given time and for 60, 80, and 100% of 1 molar sucrose solution.

Green = 100% of 1 molar sucrose solution, Red = 80% of 1 molar sucrose solution, Blue = 60% of 1 molar sucrose solution

Conclusion and Evaluation:

The experiment was carried out by placing precisely 8ml of yeast/water solution in a side arm test tube and adding exactly 7ml of different concentrations of a one molar sucrose solution. The consequent volume of carbon dioxide produced was measured using the displacement method where the side arm of the side arm test tube (in which the reaction occurred) was placed at the mouth of a water filled, up-side-down measuring cylinder under water in order to catch the gas produced. This way all carbon dioxide produced could be accurately measured. After carrying out this investigation, it becomes apparent that yeast produces carbon dioxide longer at a more constant rate if provided with more sucrose. As shown by the relatively similar rates of carbon dioxide production after 3 hours of respiring (0.322ml/min, 0.331ml/min, and 0.339ml/min) that later become more differentiated (0.185ml/min, 0.208ml/min, and 0.239ml/min), the yeast provided with the 100% one molar sucrose solution produces more carbon dioxide for a longer time than the other concentrations. The effect on the carbon dioxide production, from 8 ml of (yeast) respiring with sucrose solution, when the sucrose solution varies in concentration such that the yeast respires with 7 ml of 60, 80, and 100% one molar sucrose solution is therefore that it does not increase significantly with the concentration. However, it becomes apparent that the yeast provided with the higher concentration sucrose solutions can produce more carbon dioxide for a longer period of time.

There are, however, some limitations and weaknesses in the method of this investigation. Firstly, the volume of yeast used was not constant throughout the different trials. The reason for this was as the trials took so long, the yeast had to be mixed with water anew in for the second trial as to minimize the amount of dead cells that accumulate over time. An improvement for this would include setting up all the trials simultaneously rather than after one another, and therefore using the same culture of yeast in all trials. Secondly, the volume of carbon dioxide would increase if the side arm test tube were shaken. This results in the data being a mixture of shaking and non shaking, as the samples could not be shaken the whole time. To improve this, the samples should either not be shaken at all, or they should be placed on a vibrating platform for the duration of the experiment to ensure the constant shaking of the samples. Lastly, the environment in which the respiration took place did not remain constant as the laboratory was vented by opening windows and temperature, consequently, pressure changed with that resulting in no constant experimental environment. This could be improved by placing the side arm test tube and its respiring contents into a calorimeter such that the internal environment does not fluctuate as violently as the external one.

References:

Figure 1:

Robertson, Frankie, illus. "Yeas cell english." Wapedia. N.p., 21 Oct. 2006.
Web. 30 Jan. 2010. <http://wapedia.mobi/en/
File:Yeast_cell_english.svg>.

Figure 2:

Allan, Andy, illus. "Cellular Respiration." Sciencegeek. N.p., 7 Oct. 2008. Web.
30 Jan. 2010. <http://www.sciencegeek.net/Biology/review/
U2RespFillin.htm>.

Yeast Investigation

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