Cellular Energetics - Fermentation
& Cellular Respiration
Exercise 4 - Iodoform Test for Alcohol
A distillation apparatus may be used to concentrate the alcohol produced by
fermentation of glucose by yeast. This is possible since water boils at 100°C
while alcohol boils at 78°C. Four test tubes were prepared, each containing
2 ml of IKI, 3 ml of 1.5M NaOH, as well as one of the following:
- Tube 1 - 5 ml of Water
- Tube 2 - 5 ml of 50% Ethyl Alcohol
- Tube 3 - 5 ml of Distillate of Unfermented Yeast Culture
- Tube 4 - 5 ml of Distillate of fermented Yeast Culture
Each solution was left to stand for 45 minutes. Ethanol, if present, reacts
with iodine at high pH to form iodoform which settles out as a yellow precipitate.
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to View the Results
Answer the following questions:
- Is ethanol present in Distillate 1 or 2?
- Where did the ethanol come from?
- What is the purpose of tubes 1 and 2?
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Exercise 5 - Cellular Respiration
From the
respiration figure it is possible to see that during cellular respiration
oxygen is used while
carbon dioxide is being produced. This relationship is direct in a quantitative
sense, since for every mole of oxygen used one mole of carbon dioxide
is produced. Thus, if respiration
proceeds in a closed system the volume of gas will remain constant even though
the composition of the gas changes. If the liberated carbon dioxide is removed
then the volume of gas in a closed system will decrease. Thus, the amount of the
decrease over time will reflect the amount of carbon dioxide liberated as well
as the amount of oxygen used during respiration. We will make use of this information
to measure the overall rate of respiration in plant material (germinating seeds)
and animal material (flour beetle larvae).
Keeping this information in mind.
several simple respirometers were set up. Each respirometers consists of
a test tube with the test material , pellets of KOH suspended above the material
on glass wool, a set of tubes which join the test tube to a u-tube with fluid
and a 1 cc syringe.
The respirometers were used to measure the use of oxygen
under the following conditions:
- plant material (germinating seeds) at 20°C
- plant material (germinating seeds) at 30°C
- animal material (flour beetle larvae) at 20°C
- animal material (flour beetle larvae) at 30°C
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to View the Results
Answer the following questions pertaining to the experiment:
- If you conducted the experiment in the dark would you expect different
results?
- How could you prove that Carbon dioxide is given off during
respiration?
- Which respired more rapidly, the seeds or the flour worms?
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The flour beetle more-or-less conforms to the temperature of its environment.
This is referred to as being poikilothermic or ectothermic.
Humans are one of a large group of animals which are termed homeothermic
or endothermic.
This means that they maintain their body temperature around a certain value
(for example 37°C in the case of humans).
Answer the following questions:
- How would changes in environmental temperature (in either an upward
or a downward direction) affect respiration in a homeothermic animal)?
- Name the specific regions of a cell where the various steps of catabolism take
place.
- If you oxidize glucose with a flame in a bowl, a large amount of heat is
given off. Why doesn't the oxidation of glucose in a cell injure the cell with
heat?
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First published Sept 95: Modified Aug 05
Copyright © Michael Shaw 2005 (Images and Text)
