Fungal Physiology
Observations: Nearly all
organisms require a source of chemicals to provide energy for maintenance and
growth. Of these organisms, nearly all rely upon some kind of carbohydrate.
Textbooks indicate that glucose and fructose are found along the glycolytic
pathway. In the absence of oxygen, yeasts utilize the alcoholic fermentation
pathway to produce energy (in ATP), ethyl alcohol, and carbon dioxide. Of these
products, carbon dioxide is a gas and can be measured volumetrically as you did
in Durham tubes.
Question: What type of
carbohydrate might serve as the best
energy fuel for an organism?
Hypothesis:
Yeast make the enzymes required for fermentation of all of these carbohydrates.
Prediction:
If the hypothesis above is true, then carbon dioxide gas should accumulate
equally among yeast samples when given each of the carbohydrates.
Experiment: Each
15 mL graduated centrifuge with four 15ga needle holes in its lid will be
filled with a mixture of 7.5 ml yeast suspension (Saccharomyces cerevisiae) with 7.5 ml of 5% carbohydrate solution
(or water control). Each labeled tube should be completely full. The lids
should be twisted on securely. The four tubes will be inverted in a 400 mL
beaker that contains water dipped from the 40°C water bath. The beaker will be
placed in the water bath and observed occasionally. Time for all the tubes will
be stopped when the tube with the most gas has a meniscus at about the 10 mL
mark (record time in minutes).
Results: Record the bottom of the meniscus (or the bottom of any “foam”):
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Carbohydrate
Treatments
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5% Sucrose
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5% Glucose
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5% Lactose
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Distilled
Water
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Time = 0
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___/60 hr
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Analysis: Calculate a rate
for each treatment = =
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Units
Rate ( / )
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Decision:
The hypothesis above is rejected not
rejected
Conclusions:
The yeast cells had had not
used up their initial substrate.
The yeast cells did did
not produce invertase.
The yeast cells did did
not produce lactase.
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