Sara Catherine Paul Mourani 001294 – 030

Biology internal assessment

Sara Catherine Paul Mourani

May 2012

001294 - 030

Effect of temperature on fermentation rate of yeast

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Sara Catherine Paul Mourani 001294 – 030

Effect of Temperature on Fermentation

1. Yeast and Fermentation

Yeast, also known as poikilotherms, is eukaryotic fungi which can undergo fermentation (or anaerobic respiration) when oxygen in the surrounding is absent. Thus, the glucose consumed by the yeast reacts to form ethyl alcohol and a waste product, Carbon dioxide, through the reaction

C6H12O6 2CH3CH2OH + 2CO2 + 2 ATP

Bakers will use carbon dioxide to raise the dough in bread, thus making the bread lighter.

Many different enzymes are involved in the fermentation product, and many factors can affect their activity. The factor to be studied in this case is temperature.

The rate of fermentation can be determined by monitoring the volume value of CO2, since it is a gas, by using the method of water displacement.

2. Research question

What effect does increasing temperature have on the enzyme rate of enzymes responsible of fermentation in yeast?

3. Hypothesis (and expectations)

Increasing the temperature will increase the enzyme rate which take part in the fermentation process (= fermentation rate) but will start to decrease after the enzymes have reached their optimal temperature, and begin to denature.

4. Variable and experiment control

(a). Variables

Independent variable: In this case, the independent variable is the temperature which will be varied by the student.

Temperature will be varied by using a water bath set at different temperatures depending on the test tube number. The temperatures used will be 10 degrees Celsius, 20 degrees Celsius, 30 degrees Celsius, 40 degrees Celsius, 50 degrees

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Sara Catherine Paul Mourani 001294 – 030

Celsius, and 60 degrees Celsius. Maintain the water baths at the correct temperature throughout the experiment.

Dependent variable: Rate of fermentation (volume of CO2 formed per unit of time)

(b). Constants

Mass of yeast (amount of enzymes used)

By measuring the same mass of yeast powder for each trial using an electrical balance.

Amount of substrate, glucose, used

The source of glucose in this case will be in the form of apple juice. An equal volume of the same apple juice bottle will be used in each trial.

Time of the reaction

The time of the allocated for each trial’s reaction is one hour, since fermentation is a relatively long process.

5. Material

2 graduated cylinders

Apple juice

Water

Yeast powder

Spatula

Chronometer

Thermometer

Erlenmeyer Flask and punctured cap

1 Water bath

1 rubber tube

2 glass straws

1 watch glass

6. Procedure

This is an example of the experiment carried out at 50 degrees Celsius. The difference between this example and the other trials is the temperature at which the water bath is preheated, which is varied in all 6 trials.

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Sara Catherine Paul Mourani 001294 – 030

Make sure to thoroughly rinse and dry all the glassware prior to every trial to avoid any type of contamination.

First, prepare the glucose solution.

Using a graduated pipette, measure a volume of 100 cm3 of apple juice.

Pour the apple juice into a flask.

Dissolve the glucose in the water and mix using a stirring rod.

Set the water bath at a temperature of 50 degrees Celsius.

Incubate the glucose solution in the water bath.

Using a spatula, place little by little dry yeast into a separate graduated cylinder till 1.5 cm3 of yeast is measured. Place the yeast in a watch glass.

Incubate the test tube in the water bath for 10 minutes, once the water bath is at 50 degrees Celsius (verify this using an electrical thermometer)

During the incubation period, fill the basin with water.

Take the third graduated cylinder and place thumb on the cylinder opening, thus sealing it.

Place the cylinder opening (which is still sealed) under the water surface in the basin, than remove thumb.

Let a few seconds pass, and then take the reading of the volume on the graduated cylinder. This will be the initial volume.

Connect rubber tube and glass straw together, and place the glass straw inside of the flipped graduated cylinder.

Place another glass straw on the other side of the rubber tubing.

Connect the flask cap and the other glass straw. The setup should resemble this image:

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Taken from http://antoine.frostburg.edu/chem/senese/101/inorganic/faq/hydrogen-prep.shtml

Prepare chronometer at ‘0 seconds’.

Add yeast to apple juice in the flask and immediately start the chronometer.

Seal the flask with the cap.

Slightly rotate the flask to mix the solution to homogenize the yeast-apple juice mixture.

After an hour, read the volume on the graduated cylinder. This will be the final volume.

Repeat this procedure for tubes 1, 2, 3, 4 and 6.

7. Data collection and processing

Tube number Initial volume in cm3

Final volume in cm3 Time of reaction in min

1 602 603 604 605 606 60

Table 1 – Format for data collection

You can first collect the data by putting it in table form, using this format

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Sara Catherine Paul Mourani 001294 – 030

Then for data processing, we calculate the volume difference to obtain the volume of CO2 produced. This is then decided by the time of the reacting to obtain the reaction rate.

Tube number Difference of Final and initial volume

in cm3

Time of the reaction in min

Rate of reaction (Volume of CO2/Time) in cm3/min

1 602 603 604 605 606 60

Graph formatting

After having found the rates, plot the value on a graph of rate versus temperature (temperature being on the horizontal, and rate being on the vertical) and observe how the rate progresses depending on the temperature of the medium.

Safety precautions in Laboratory:

Tie hair if below shoulder length.

Do not consume any of the chemicals or foods used, as they may be contaminated, thus hazardous.

Use equipment carefully; do not burn yourself when using hot solutions or water bath.

Wear gloves and lab coat to avoid contact with chemicals and the student’s clothes or skin.

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