Fermentation in Yeast TN

8/9/2019 Fermentation in Yeast TN

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Teacher Notes

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Fermentation in Yeast

Objectives

Students explore two of the principle metabolic processes, aerobic and anaerobic cellular

respiration, used by facultative anaerobes to produce energy, and identify factors that affect

when alcohol fermentation (anaerobic cellular respiration) occurs in yeast. During thisexploration students investigate:

! Byproducts produced from both aerobic cellular respiration and alcohol fermentation in yeast

! Quantify the rate of both processes using sensors

! Sugars fuel the fermentation process within yeast

Procedural Overview

Students gain experience conducting the following procedures:

! Assembling a closed, sugar-rich, environment in which activated yeast cells can metabolize

! Measuring oxygen gas and ethanol gas concentrations within the closed environment using

sensors

! Associating each of the measurements with one of two metabolic processes occurring within

the yeast cells

! Designing a short experiment that identifies whether lactose, maltose, or sucrose affects the

fermentation process within yeast

Time Requirement

! Preparation time 25 minutes

! Lab activity 90 minutes

Materials and Equipment

For each student or group:

! Data collection system ! Dry yeast solution, 1 L1

! Oxygen Gas Sensor ! 0.5M Sucrose solution, 500mL2

! Ethanol Sensor ! 1% Ethanol (for sensor calibration)

! EcoChamber ! Beaker, 500mL

! Magnetic stirrer with stir Bar

! 3 other types of sugar (not sucrose)3

! Beaker, 1,000mL

1 To formulate activated dry yeast using dry yeast and water, refer to the Lab Preparation section.

2 To formulate 0.5M Sucrose solution using Sucrose and water, refer to the Lab Preparation section.

3 Refer to the Lab Preparation section for alternative sugar suggestions.




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Safety

Add these important safety precautions to your normal laboratory procedures:

! Ensure that you understand and adhere to safe laboratory practices when performing

any activity in the classroom or lab.

! Use personal protective equipment such as safety glasses or goggles, gloves, and aprons

when appropriate.

Background

Are yeast aerobic or anaerobic organisms? Yeast are actually single-celled organisms that are

facultative anaerobes, organisms that have the ability to undergo aerobic respiration in the

presence of oxygen and anaerobic respiration in its absence. With oxygen present, yeast will

preferentially undergo aerobic respiration because they can make 36 ATP molecules per glucose

molecule through aerobic respiration, compared to the 2 ATP molecules produced through

anaerobic respiration.

In this activity, yeast will use the dissolved oxygen and the sugar in the water solution as the

reactants in the equation:

C6H12O6 + 6O2 ! 6 CO2 + 6H2O + energy (primarily stored in ATP molecules)

As time progresses, you should see a decrease in concentration of oxygen because the yeast cells

use it to create ATP. As oxygen becomes less available the yeast will change their metabolic

pathway to alcohol fermentation to continue producing the ATP required for cellular processes.

C6H12O6 ! 2CO2 + 2C2H6O + energy (primarily stored in ATP molecules)

The fermentation process does not produce ATP directly but allows NAD+ to be recycled into

NADH which allows glycolysis to continue. The net yield for alcoholic fermentation is only 2

molecules of ATP per glucose molecule. As more cells begin to ferment, the concentration of

ethanol in the chamber will increase. This fermentation process is similar in many ways to lactic

acid fermentation which occurs in muscle cells when oxygen levels are low. Most students will

have direct experience with lactic acid fermentation because it is largely responsible for the

“burn” felt in muscles following intense exercise.

Lab Preparation

Before the Lab

1. Prepare the yeast solution at least 30 minutes before the lab begins. To make 1 liter (L) of

solution, add 20 grams (g) of dry baker’s yeast to 1 L of warm water (30 to 35 °C). Alter the

proportions if you need to make more than 1 L. Baker’s yeast from grocery stores works very

well, but be sure to check the expiration date. Yeast purchased in bottles of 100 g or larger

are widely available and are often more economical than packets. Once you have made the

initial solution, it can be stored at room temperature until ready for use. Just make sure thatit stays between 20 °C and 45 °C.

2. To prepare the 0.5 M sucrose solution:

a. Measure 171 g of sucrose (table sugar).

b. Place the sugar in a beaker or bottle.

c. Add distilled water to make 1 liter of solution.



Teacher Notes

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One liter is enough for two groups, so alter the proportions so that each group receives

500 mL of solution. You can store the solution at room temperature.

3.

You will need 1% ethanol solution to calibrate the ethanol sensor.

4. To prepare the ethanol sensor for use, connect it to a data collection system that has been

plugged into an electrical outlet before starting the lab. The sensor will warm up and

perform optimally during the lab.

5. Have at least three other types of sugar available to students for the inquiry part of the lab.

Lactose, maltose, and glucose are excellent choices as they will provide a variety of results.

Be sure that you have enough for each group to make at least a 0.5 M 500 mL solution of the

sugar they choose.

Sample Data

The following screenshots display examples of data similar to what students should expect to

see.




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Answer Key

Analysis Questions

1. Did the O2 concentration in the chamber increase or decrease? Does this indicate that

respiration occurred? Explain why or why not?

The O2 concentration in the chamber decreased 4% (student numbers may vary slightly, but they should cite

collected data in their response) during data collection period. This indicates that oxygen was being consumed

by the yeast cells as they conducted aerobic respiration. If the yeast cells had been creating ATP solely through

anaerobic respiration, no change in oxygen levels would be observed.



Teacher Notes

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2. If you were to allow the yeast sample to sit for a very long time, do you think the O2

concentration would eventually go to zero? Explain why or why not.

While theoretically the oxygen concentration would drop to zero if the yeast respired over a long enough period

of time, the data suggests that below a certain concentration the yeast are primarily conducting alcohol

fermentation and oxygen consumption stabilizes.

3. Did the amount of ethanol in the chamber increase or decrease? Does this indicate that

fermentation occurred? Explain why or why not?

The amount of ethanol in the chamber increased 0.8% (student numbers may vary slightly, but they should cite

collected data in their response) during data collection period. The presence and gradual increase in the amount

of ethanol in the chamber indicates that the yeast are conducting alcohol fermentation. The rate of ethanol

production should increase over time as oxygen becomes less available for aerobic respiration.

4. Based on our data, what conclusion(s) can we draw in terms of whether yeast are facultative

anaerobes? Support your conclusion using your data.

In the lab we observed evidence of yeast cells conducting aerobic and anaerobic respiration, suggesting that

they are facultative anaerobes. We observed a decrease in the oxygen concentration, which suggests the yeast

cells were aerobically respiring. As the amount of available oxygen decreased there was an increase in the

ethanol concentration, which suggests the yeast was conducting alcohol fermentation.

Design Your Own Experiment Sample Responses)

Students are encouraged to develop their own inquiry based on questions that have arisen in the

course of completing the guided portion of this lab. The following sections are sample responses

that students may develop as well as suggestions and activity ideas.

Question

Students should write their question so it includes the independent and dependent variable(s)

they will monitor. Some investigable questions include:

! If the sugar was changed to (lactose, maltose, etc.), would alcohol fermentation still occur?

! Would one type of sugar make fermentation happen more rapidly, or create more ethanol, than

the other types?

Prediction

After conducting the guided portion of this lab, students have enough information to formulate a

hypothesis that develops a cause and effect relationship between an independent variable and

dependent variables, which should answer the questions: What do you think will happen? Why

do you think so? One example of a hypothesis is shown here:

! We predict that if the sugar is changed to lactose, alcohol fermentation will occur because, like

sucrose, lactose is a disaccharide.

Materials

Many inquiries can be completed with the original materials for the guided portion of this lab.

Additional materials may include:

! Lactose, maltose, glucose, fructose, and other sugars

Procedure

Students may add pages of text boxes and write their procedure in the data collection system,

they can write their procedure in a lab notebook, or they can process their procedure in a

computer file and submit it to you electronically. Whatever way the procedure is prepared, it




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should conform to certain guidelines and should be approved by you before the students begin

their inquiry. Also, clarify the safety parameters for their investigations before they begin.

Guidelines include the following:

! The procedure should be a numbered list.

! Sentences should be concise, well-written, complete, and effectively communicate each step.

! Both independent and dependent variables should be described, and students should indicate

how the independent variable will be changed and how the dependent variables will be

measured.

! Additional controlled variables that are to remain constant should be described.

! The method of displaying collected data is identified. Students choose a graph, table, digits

display or meter.

! Students should record observations while they collect data.

Building a Page for Data Collection

Instructions are provided for building a page that includes a table, graph, digits display, or

meter.

Students begin by selecting Add New Page . From there, they can build a page

for data collection or for writing notes and observations. To collect data they must

select a sensor and then select the type of display they want to use: table, graph,

digits display or meter.

To record observations or write notes, students choose a large text box . They will be able to

enter text on the entire page. Another option is to place a data collection box, such as a graph

and two small text boxes, on the same page. Students should experiment with different design

elements until they find an arrangement that suits their purpose.

Analyze Your Data

Students will analyze their data, including any mathematical and graphical analysis, such as

finding the mean or the percent increase.

Draw Your Conclusion

Students should state whether or not their hypothesis was correct. They should summarize how

a change to their independent variable caused a change of their dependent variable(s) in a

predictable way.

Make the Connection

Students take what they have learned in their own experiment and add it to what they have

learned from the guided portion of the lab to answer the overarching challenge of the lab.

! When the sugar was changed did the yeast cells continue to exhibit an ability to perform

anaerobic and aerobic respiration?

! How did the results of your experiment compare to the guided experiment?



Teacher Notes

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Your Experiment – Assessment Rubric

Lab Sections A Good Answer A Better Answer The Best Answer

Driving Question Written as an exploration or

testable question

Written as a question;

includes at least one variable

Written as an if–then question;

includes both the independent

and dependent variables

Hypothesis Reflects what studentsexpect to happen

Reflects what studentsexpect to happen and why

Merges the driving questionwith what students expect to

happen and why

Procedure Has teacher approval Has teacher approval Has teacher approval

! Materials list Students use the same

materials they used in the

first part of the lab.

At least one essential new

material listed

Refers to materials used in a

different way or lists new

materials

! Clear directions Numbered list Numbered list, well-written Numbered list, concise, clear

steps; thorough

! Independent,

dependent, and

controlled

variables

Identifies the independent,

dependent, and controlled

variables

Identifies and explains how

variables will be controlled or

measured

Identifies and explains how

variables will be controlled or

measured, and how the

independent variable will be

changed

! Sample rate and

sensor

Includes sample rate or

sensor

Includes sample rate and

sensor setup

Includes sample rate, sensor

setup, and how it will be used

! Observations Includes an observation for

each run

Observes both independent


during each run

Describes behavior of both

independent and dependent

variables and all conditions

during the run

Analyze Data Collected one run of data

shown on a graph or in a

table; axes or columns are

correctly labeled

Collected multiple runs of

data; axes or columns are

correctly labeled; conditions

are correctly labeled

Collected multiple runs of data;

axes or columns are correctly

labeled, conditions correctly

labeled; pertinent values or

trends indicated

Analysis

! Mathematical or

graphical

analysis

Some mathematical or

graphical analysis is shown

or with a statistics tool

Pertinent calculations, such

as the mean or change in

value, are calculated and

visually displayed

Pertinent calculations, such as

the mean or change in value,

are calculated and different

conditions are compared

visually

! Conceptual

analysis

Explains the relationship

between the independent


Uses data to explore the

cause and effect relationship

between the independent


Uses graphs and tables to

explore the cause and effect

relationship between the

independent and dependent

variables

Conclusion Answers the conclusion

question and states whether

or not their hypothesis was

correct

Answers the conclusion

question and states whether

or not their hypothesis was

correct and answers their

(driving) question

More extensively answers the

conclusion question and states

whether or not their hypothesis

was correct and answers their

(driving) question

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Fermentation in Yeast TN