July 26, 2014

Homework Help: biology help?

Posted by sam on Friday, February 15, 2013 at 4:51am.

In 1857, Louis Pasteur discovered that yeast is a living organism. The
activity of yeast causes fermentation bakers yeast, Saccharomyces
cerevisiae, has been used for centuries in the production of bread, beer and
wine. In the absence of oxygen, yeast is able to derive energy from nutrient
carbohydrates by switching from aerobic to anaerobic respiration. In the first
step of anaerobic respiration, known as glycolysis, monosaccharides such as
glucose or fructose are oxidised to form pyruvate, with the net release of
energy in the form of ATP
Step 1 Glycolysis
glucose + ADP + NAD → pyruvate + NAD.2H + ATP
In the second step (alcoholic fermentation) the pyruvate is reduced to form
ethanol and carbon dioxide:
Step 2 Alcoholic fermentation
pyruvate + NAD.2H → ethanol + NAD + CO2
After reading Chapters 5 and 6 of Book 5, an enterprising OU student
decided to investigate the anaerobic respiration of yeast in the presence of
different sources of carbohydrate. The student had a job as a laboratory
technician in a school and so was able to set up the apparatus shown in
Figure 1 and carry out the investigation using each of the mixtures described
in Table 2 in turn. Each experiment was carried out at room temperature
(20 C).
Table 2 The contents of the reaction mixture in each of the five experiments. You can assume that the
starting concentrations of the carbohydrate solutions were the same (i.e. same mol dm
Experiment A B C D E
A)5 cm3 yeast
suspension +
1 cm3 distilled
B)5 cm3 yeast
suspension +
1 cm3 glucose
C)5 cm3 yeast
suspension +
1 cm3 sucrose
D)5 cm3 yeast
suspension +
1 cm3 starch
E)5 cm3 yeast
suspension +
1 cm3 starch
At the start of each experiment the measuring cylinder was filled with water
and quickly inverted in the trough of water and placed on the beehive shelf
(a platform with holes that allows free movement of water in or out of the
measuring cylinder). The reaction mixture was made up in the bottle and the
stopper quickly replaced so that any gas given off by the yeast mixture
travels through the tube and is collected in the inverted measuring cylinder,
the gas pushing down the water as shown in Figure 1. The volume of gas
produced was measured at 5-minute intervals for 30 minutes. A graph
showing the results of these five experiments is shown in Figure 2.
Q)The experiment could be extended to see how temperature affects the
way the yeast respires. Predict the effect on the results of experiment B
(5 cm3 yeast suspension + 1 cm3 glucose solution) if it was repeated (i)
at 4 C and (ii) at 60 C and give a brief explanation for each of your

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