In 1857, Louis Pasteur discovered that yeast is a living organism. The
activity of yeast causes fermentation – baker’s 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
–3).
Experiment A B C D E
Reaction
mixture
A)5 cm3 yeast
suspension +
1 cm3 distilled
water
B)5 cm3 yeast
suspension +
1 cm3 glucose
solution
C)5 cm3 yeast
suspension +
1 cm3 sucrose
solution
D)5 cm3 yeast
suspension +
1 cm3 starch
solution
E)5 cm3 yeast
suspension +
1 cm3 starch
solution
containing
amylase
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
predictions.
I would need to see the figures to be able to help.
this is an OU tma question! do the bloody reading you lazy sod- it won t help you in the exam!
i second anonymous and would also like to add that this breaks the plagerism clause of the course...
I would like to know why the first part of the experiment A was done with distilled waetr
To predict the effect on the results of experiment B (5 cm3 yeast suspension + 1 cm3 glucose solution) if it was repeated at 4 °C and 60 °C, we'll need to understand the relationship between temperature and yeast respiration.
At higher temperatures, the metabolic processes in yeast, including respiration, generally occur at a faster rate. However, there is an optimal temperature range for yeast activity, beyond which the enzymes involved in respiration may denature and become less efficient.
(i) At 4 °C:
If the experiment is repeated at 4 °C, which is significantly lower than the optimal temperature range for yeast activity (around 25-30 °C), it is likely to have a negative effect on the results. The lower temperature will slow down the metabolic processes in yeast, including glycolysis and fermentation, resulting in a slower rate of CO2 production. Therefore, the volume of gas produced at each time point may be lower compared to the original experiment conducted at 20 °C.
(ii) At 60 °C:
If the experiment is repeated at 60 °C, which is significantly higher than the optimal temperature range for yeast activity, it would likely have an even more detrimental effect on the results. The high temperature can denature the enzymes involved in yeast respiration, rendering them inactive or less efficient. This could impede the glycolysis process and reduce the production of CO2. Consequently, the volume of gas produced at each time point may be significantly lower compared to the original experiment conducted at 20 °C.
In summary, if the experiment is conducted at 4 °C, the rate of CO2 production is expected to decrease, leading to a lower volume of gas, while at 60 °C, the rate of CO2 production may be severely hindered, potentially resulting in a very minimal amount of gas being produced.