Question

Report Sheet                                                                      Lab Section:                     .

Energy Harvest – Fermentation in Yeast Exercise

Data:

Group No.	Sugar Used	Rate of Respiration mean	Rate of Respiration Average per sugar
	Glucose	5.82
	Glucose	5.33
	Glucose	3.76
	Glucose	6.11	5.7
	Glucose	7.30
	Glucose	5.86
	Sucrose	7.23
	Sucrose	7.39
	Sucrose	6.72
	Sucrose	6.37	6.9
	Sucrose	6.84
	Sucrose	6.84
	Lactose	7.90
	Lactose	1.17
	Lactose	1.57
	Lactose	1.53	2.4
	Lactose	0.57
	Lactose	1.73
	Fructose	5.44
	Fructose	8.80
	Fructose	5.74	6.9
	Fructose	7.31
	Fructose	7.12
	Fructose	7.14

Table 1     Fermentation Exercise Data      This table shows the fermentation rates of various sugars by yeast collected from the class.

Analysis and Questions of Results:

1. Generate a hypothesis and identify the independent, the control treatment, the dependent, and

two control varialbes for the conditions of the this lab.

2. Graph (your Figure 1) the class data on a separate piece of graph paper to show the average rate

of respiration vs. sugar type. Label the graph fully and give it a proper title (Appendix A). Use the space below to interpret the trends seen on your graph by referring to the graph by its figure number.

3. Considering the results of this experiment, can yeast utilize all of the sugars equally well? Quote

specific numerical values by citing your figure number to answer this question.

4. Hypothesize why some sugars were not metabolized while other sugars were metabolized?
5. Hypothesize why the sugars that were metabolized were metabolized at different rates?

Refer to the perspectives of this lab to answer the following questions.

1. Write the overall balanced chemical equation for both aerobic respiration and anaerobic

respiration of glucose by yeast and explain how they differ in terms of products.

2. Explain why there are different numbers of ATP produced when yeast metabolize glucose

aerobically vs. anaerobically.

3. Outline the steps of the scientific method and explain why scientists always attempt to follow

the scientific method when doing experiments?

Answer 1

1.) This is an experiment set up to study the rate of respiration under the influence of different types of sugars.

Control treatment-Yeast inoculum without any sugar substrate

Independent- Amount of inoculum

Dependent- Sugars

Variables- Rate of respiration, Metabolic pathways

2.)

1

The trends as per the graph above show that the fructose and sucrose were utilized easily and can influence the rate of respiration while Lactose being utilized least.

3.) Yeast cannot utilize all the sugars equally well. The sucrose and fructose are being used equally having avg. rate of respiration of 6.9 while the lactose has the least rate of respiration i.e. 2.4.

4.) Lactose is not metabolised at a substantial rate. First, the lactose is a disaccharide and yeast does not have ability to utilize lactose due to the absence of the enzyme lactase.

5) The metabolism of the different sugars depends on the complexity of the sugar on the pathway it takes.

Glucose and fructose are monosaccharides, so they can be utilized easily

Sucrose is a disaccharide made of  Glucose+Fructose
Sucrase will split sucrose.
Isomerase will convert Fructose to Glucose.

Thus, 1mole sucrose will yield 2moles of glucose (when All of them is converted to glucose).

Lactose is a disaccharide made of Glucose + Galactose
Lactase will split the lactose and Transacetylase will convert Galactose to Glucose.
However, readings suggest that yeast does not have the gene for lactase and this is why the lactose sugar remains intact or barely used.

6.) The equation for aerobic respiration in yeast-

C6H12O6 → 6C02 + 6H2O + 38ATP

The equation for anaerobic respiration of glucose in yeast-

C6H12O6 → 2C2H5OH + 2C02+ 2ATP

The glucose undergoes incomplete oxidation in case of an anaerobic reaction. This partial breakdown leads to the formation of ethanol or ethyl alcohol. Since oxygen is absent to serve as a terminal electron acceptor, therefore, other molecules such as nitrate, sulphate or fumarate serve as the terminal electron acceptor. Whereas in the case of aerobic respiration, oxygen serves as the terminal electron acceptor and there is complete oxidation of glucose which leads to the formation of water and carbon dioxide.

7.) The difference in the production of ATP is due to the difference in pathways taken to metabolize the glucose. During anaerobic respiration, only the first step is similar to that of cellular respiration (glycolysis) which produces 2 ATPs. Since oxygen is not present the respiration cannot continue to the last step (electron transport chain) which produces the most ATPs and gets terminated at very first step limiting the production of ATPs.

8.)Steps of scientific methods-

observation.

question the observation

Form a hypothesis.

prediction based on the hypothesis.

Test the prediction by doing the experiment.