# Biochemical Pathways

Yeast synthesizes ATP through two major biochemical pathways: respiration and fermentation (both produced CO2). This experiment will test yeast’s ability to metabolize sugar for energy. You can complete this activity in lab or even online without the materials.

The Experiment
Using four 250 ml flasks, add 125 ml of warm water and 25 grams of baker’s yeast. Add the following amounts of sugar to the four flasks and mix well:

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After mixing the yeast/sugar solution, affix a rubber balloon over the mouth of each flask. Incubate the flasks in a warm environment for 24 hours.

1.    Recall what you know about the reactants and products of cellular respiration, write down the chemical reactions you expect to occur if cellular respiration and or fermentation were to occur

2.    write a hypothesis about what you think will happen to each of the flasks:

3.    Predict the outcome. Use the model flasks below and draw what each balloon will look like at the end of the 24-hour incubation period.

Next, quantify the volume of gas that is produced when the yeast metabolize the sugar in each flask.  The easiest way to calculate the volume of gas in a balloon is to measure how much water each balloon can displace.  One liter of water is the equivalent of 1000 cubic centimeters (cm3).  If one of your balloons displaced 209 mL of water, what was the volume of the balloon? (hint 1 mL = 1 cm3)

4.    The amount of water displaced from each of the four balloons is recorded in the table.  Calculate and record the appropriate volumes of each balloon in the table.

Quantity of
sugar in flask (grams)    Amount of water displaced (ml)    Volume of balloon (cm3)
0    24
1    91
2    194
4    378

5.    Graph the effect of sugar quantity on respiration in yeast as measured by CO2 production.  Produce a bar graph with a title, and be sure to label the axes, mark an appropriate scale on each, and include units. [Hint: the independent variable, quantity of sugar added, should be plotted on the horizontal axis; the dependent variable, volume of CO2 produced, should be plotted on the vertical axis.]

6.    Was your hypothesis correct?  Explain why or why not using the data

7.    What if you added a few sprigs of Spanish Moss to each flask, added a wet paper towel and sealed the mouth of the flask with a cork. You keep the flasks in the sun. Predict- in which flask will the Spanish Moss show most prolific growth, and why?

8.    Write down the summary reaction of the process carried out by Spanish Moss to attain growth.

Spanish Moss: Tillandsia usenoides

Spanish Moss is an epiphytic plant (grows on other plants for support) which gets moisture from the air and thrives well if given CO2, and sunlight.

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