Fikriye İdil Kaya

Canan Çermen

11H, IB SL Biology

Haziran 11, 2010

Word Count: 0

Does the type of any added mineral effect

the fermentation rate of yeast?

Aim: To measure the difference between fermentation rates of yeast samples those contain varied minerals

Introduction

The activated dry yeast will start fermentation, producing carbon dioxide. The rate of carbon dioxide production will therefore give the rate of fermentation –Although other lively processes might cause gas production to occur, they will not have critical influences on the data since the rate of carbon dioxide production by fermentation is highly over the rate of production of other gases. The carbon dioxide gas will be collected from yeast samples, which contain varied minerals, and the amount of carbon dioxide collected from those samples will be noted to give a useful comparison among copious fermentation rates. In the experiment, groups are as follows:

Control group

Group A: 20 mL water, 0.50 g glucose, 2.00 g yeast

Experimental groups

Group F: 20 mL water, 0.50 g glucose, 2.00 g yeast, 2 mg ferric chloride (contains mineral iron mineral: Fe)

Group C: 20 mL water, 0.50 g glucose, 2.00 g yeast, 2 mg calcium chloride (contains mineral calcium: Ca)

Group N: 20 mL water, 0.50 g glucose, 2.00 g yeast, 2 mg sodium chloride (contains mineral sodium: Na)

Research Question: Does the type of an added mineral affect the fermentation rate of yeast?

Null hypothesis: The type of an added mineral does not affect the fermentation rate of yeast.

Alternative Hypothesis: The type of an added mineral affects the fermentation rate of yeast.

Prediction: As the mineral type added to the fermentation site of yeast changes, the fermentation rate changes and so does the amount of carbon dioxide gas produced by the yeast.

Control variables: The type and amount of yeast (2.00 g per tube); type, amount (20 mL), and temperature of water added to the yeast to make it germinate; amount of mineral added to the yeast as solved in the water (2 mg of each type); type of gas-collecting material and graduated cylinders and beakers; room temperature before and after the experiment.

Independent variable: The type of mineral added to the yeast to germinate.

Dependent variable: The amount of carbon dioxide gas collected from yeast sample in 20 minutes.

Materials

4 X Gas-collecting aparati: 100 cm3 ± 0.1 cm3 thin, graduated, glass gas-collecting tube; 400 mL graduated glass beaker; 400 mL water; glass tube (to perform the experiment in); plastic pipette (for connection between the glass tube and gas-collecting tube) joined to an impermittable lid of the glass tube

4 X iron stand with two clasps per stand (to enjoin the glass tube and the gas-collecting tube)

3 X plastic container (to measure the amount of the minerals) 20 mL ± 0.25 mL graduated cylinder ± 0.1 s timer (preferrably electronic) ± 0.1 oC thermometer (preferrably electronic) 2000 g ± 0.01 g balance 2 mg of dehydrated salts containing the minerals (ferric chloride, calcium chloride,

and sodium chloride) 2.00 g glucose powder Distilled water (20 mL ± 0.25 mL per each group) 4 X 100 mL graduated glass beaker (three to prepare the solutions, one to put the

distilled water) 4 X Glass rod (to mix the solutions) Electronic heat Extra beaker (to reduce the boiled water’s temperature down to 50 oC)

Method

1. Put the safety gloves, glasses, and aprons on.2. Fill the 400 mL glass beakers with water and set each one of them next to one iron

stand.3. Attach two clasps to each iron stand and attach one glass tube to the lower clasp.4. Fill each gas-collecting tube completely with distilled water, and put a finger on it to

enclose it and not to let any water out or any air in during the next step.5. Turn each gas-collecting tube upside down, dip it into water in a 400 mL beaker, and

attach it to the iron stand using the upper clasp, stabilizing its position in the water beaker.

6. For each group, measure 2.00 g yeast using the balance and plastic container, and add the yeast into dry and clean glass tube attached to the stand.

7. For each group, measure 0.50 g glucose; for the experimental groups, measure 2 mg of salt (each salt into a different group). Add those into the 100 mL graduated glass beakers.

8. Heat 100 mL distilled water using the heater and once it boils, mix it in the extra beaker with distilled water at room temperature to obtain 80 mL water at 50 oC.

9. Add 20 mL distilled water at 50 oC into each of the four 100 mL graduated glass beakers.

10. Mix the solutions in experimental groups’ graduated glass beakers till they become homogenous –keep the process no longer than 1 minute not to cool down the water.

11. Set the plastic connection pipette by placing the uncovered under the water in the 400 mL beaker so that any gas that will come out of it will directly climb up the gas-collecting tube –which is now filled with water only.

12. Measure the room temperature as well as the solutions’ (for the experimental groups) and water’s (for the control group), making sure that they are the same.

13. Immediately add the salt solutions into experimental groups’ glass tubes and distilled water into the control-group’s and close the tubes’ lids, which are attached to the plastic pipette –the faster the better for steps 8 to 11.

14. Observe the changes in the amount of gas collected in the gas-collecting tube for 20 minutes.

15. Measure the room temperature, record any changes.

The Experimental Setup (30 seconds after the experiment was initiated):

Data Collection

Raw Data

Table of AppearancesGroups Initial Appearance Final Appearance

A The sample is cream colored and dense regions are seen on the bottom and top of the liquid. Liquid has a transparent

creamy color.The sample became foamy, keeping its

initial color.

NC

FYellowish brown and dense regions on the bottom and top of the liquid are visible. The regions contain swollen yeast

cells; liquid has a transparent brownish color.

The room temperature was kept constant throughout the whole process, at 26 oC. The temperature of the water added to the yeast varied between 47.4oC to 47.7oC, which was not considered as an error since the variation was too small to take into account.

Table of Gas CollectionGroups Initiation time / s ± 0.005

secondReaction time (20.00 s –initiation time) / s ± 0.01

Volume of collected gas / cm3 ± 0.05 cm3

A 9.10 10.90 22.6N 4.30 15.70 23.8C 8.20 11.80 23.6F 12.05 17.50 17.2

The initial appearance of groups A, C, and N. The initial appearance of group F.

Data Process

Since a considerable time passes before the fermentation begins, it should have affected the results. To find the rate of these reactions, time of the reactions must be calculated and called Data T. Then, the amount of gas produced during the reactions must be divided by Data T for each group of reaction, to find the rate given by the volume of collected gas divided by the reaction time in cm3 s-1.

Such a calculation for Group A will be as follows:

Gas collection rate = R = (Volume of collected gas / cm3 ± 0.05 cm3) / (Reaction time / s ± 0.01)

RA = 22.6 / 10.90 = 2.07 cm3 s-1

Table of Gas Collection RateGroups Gas Collection Rate / cm3 s-1

A 2.07N 1.51C 2.00F 0.98

2.5

2.0

1.5

1.0

0

An alternative way to find the rate is to find the slope of the graph of volume of collected gas versus reaction time:

For each group’s data, to draw the graph of volume of collected gas versus reaction time, whose slope will give the rate of reaction, an equation shoudl be generated. The formulae of group A can be generated as follows:

Since the reaction starts at time = 0 s and volume = 0 cm3, initial point has coordinates of 0. Then the initial point = I = I(0,0)

At the end of the reaction, the final point for group A = A = A(10.9, 22.6)

Change in the time is taken as the x coordinate and volume as y coordinate since the slope, y divided by x will give the rate, which is the change in volume over the change in time.

Slope of the equation = m = (y1 – y2) / (x1 – x2) = 22.6 / 10.9 ≈ 2.07

EquationA: y = mx = 2.07 x

Using the same formulae to find the equation of each group, the graph below can be obtained:

Conclusion

Looking at the graph above, rate increases as one moves from F to N, C, and A. The results of rate show that if RA is approximately 4n, n being a constant number, RN, RC, and RF are around 3n, 4n, and 2n in a row. Using approximations is suitable in this case as inaccuracies and imprecisions could have occured.

Its group having a very close rate to the control group’s, calcium mineral has almost no effect on the rate of the fermentation reaction of yeast. Sodium has decreased the rate by a ratio of 4 to 3, and iron decreased it even more with a ratio of 4 to 2, causing almost a 50 % decrease. Since groups with different minerals had different rates, the alternative hypothesis was correct.

Evaluation

For a better set-up, the room temperature could have been kept constant. The measurements were held accurately, since the smallest significant figure was three, which belonged to the electronic timer. The greatest error in the experiment was the yeast itself since its life activities, which includes fermentation too, could never be predicted; starting fermentation quickest in one tube and later in the other. If the yeast was cultivated as a whole and was seperated after the gas exchange started, also adding the minerals after the separation, the rae could have been observed more throughly. More gucose could be added to increase the rates, therefore enabling the differences to be detected more efficiently in a shorter time. If the gas release was observed in a specified time period for all samples, such as in every 20 seconds, the rate could be detected more accurately. This way, any variations of the rate could also be noted, so instead of having a straight line graph for the rate determination using the slope, a more accurate graph could have been drawn. Having a larger set-up with more yeast in every group would also help detecting the rate differences, since the rate difference would be multiplied by a power of number of added yeasts; causing a huge diference and more accuracy in determination of this difference among the rates of various groups.