Fermentation
Purpose: To investigate the effect of temperature on the fermentation of glucose by bakers yeast.
Hypothesis: If to separate tubes of 20% glucose solution with 1 mil of yeast is added to battery jars filled with 20 and 38 c water then the warmer one will cause the yeast to ferment at a quicker rate.
Materials:
-2 test tubes (100 mm. Long x 11 mm. I.D.)
-2 ones-hole stoppers (size 00 w/3 mm. Hole)
-Glucose
-Bakers yeast suspension
-Balance
-Molding clay
-Submersible test tube racks
-Pins
-Masking tape
-Wax pencil
-10 ml. pipette w/pump
-50ml. graduated cylinder
-Dropping pipette
-Ice
-Stirring rods
-Thermometer
-Battery jars (2)
1. Prepare a 20% glucose solution by mixing 8 g. of glucose with 32 ml. water.
2. Prepare two water bathes, one at 15 degrees C and another at 38 degrees C using battery jars, ice, and warm water from the tap. Be sure that the water baths are deep enough for your respirometers to be completely submerged.
3. Prepare a data chart that will allow you to record the number of bubbles you see per minute for ten total minutes.
4. Prepare the two respirometers as shown to the right. Using a 10 mL. pipette and pump, put 4 mL. of the 20% glucose solution into each test tube. Add 1 mL. of yeast suspension to each tube after stirring the suspension completely. Mix by gently batting the tube bottom with one forefinger while gripping the top of the test tube tightly with the thumb and forefinger of the opposite hand. Put a one-hole stopper on each test tube, being sure that it seals the tube. Stick a pin with a tape flag into the stopper to identify the tube as yours. Knead and stick a small amount of modeling clay to the bottom of the test tube to be sure the respirometer sinks to the bottom of the water bath
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. Place one respomiter into the 20º water bath and place the other into the 38º water bath. Add ice or warm water to the water baths as needed to maintain their respective temperature. Allow the respirometers to sit undisturbed for three minutes, so that their contents will come to the temperature of the water bath. After three minutes, count the number of bubbles that rise from the stopper opening per minute for a total of ten minutes. Record these numbers in your chart.
6. perform a responsible clean up by washing out then drying the test tubes and stoppers, remove the tape flags from the dried pins and throw the tape in the trash. Return pins, test tubes, and stoppers back to where you obtained them from. Your instructor will take care of the water baths.
Observations and results:
we observed that in the warmer water bath the yeast did ferment faster because we could see more bubbles coming from the test tube then the test tube in the cooler water bath. In the class data table you can see that in the 20º water bath the class total was 9 bubbles with an average of 1.5 and in the 38º Celsius water the total was 556 and the average was 92.6 this shows a big increase in the amount of bubbles
Analysis and conclusion:
The data shows that the group’s hypothesis was in fact correct and the yeast fermented faster in the warmer water bath.
Some possible mistakes in this lab would be incorrect water temperature or an incorrect amount of glucose solution. Another mistake could be that we added too much or too little amounts of yeast or that some of the yeast was not active.
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