Exploring cellular respiration in yeast

Scientific Theme(s):

Life Science

*Natural History and Biodiversity

*Ecological Interactions

Grade Level(s):

6-8

9-12

Lesson Duration: Two 1 hour exploration sessions

OverviewCellular respiration is a series of metabolic reactions essential to all living cells. Respiration releases energy from sugars and stores it in the form of adenine triphosphate (ATP). ATP is the basic energy currency for cell processes. Respiration can take place in the presence or absence of oxygen (aerobic vs. anaerobic conditions). For yeast, anaerobic respiration is known as fermentation, and produces carbon dioxide along with ethanol or lactate as the primary waste products, while aerobic respiration produces carbon dioxide and water as the primary waste products (Campbell and Reece, 2008).

In this lesson, students will use the scientific method in one instructor-guided experiment and one student-designed experiment to explore cellular respiration in yeast. When yeast is mixed with a sugar source and water, foam forms, and may be measured as a proxy for carbon dioxide production. By comparing respiration rates between different water temperature and sugar sources, students can determine optimal conditions for yeast respiration. An environment that is too cold, too hot, or lacking in food will result in lowered rates of respiration or death.

ObjectivesStudents will…

1. Understand the basic concepts of cellular respiration2. Understand the scientific method, and how to apply it3. Learn how to design a controlled lab experiment4. Practice measurement skills using thermometers and scales5. Practice recording scientific data and graphing results6. Practice drawing conclusions based on data analysis

Grade Level Expectations (GLEs) Addressed1. Science as Inquiry and Process:

a. [6-8] SA1.1 - The student develops an understanding of the processes of science by asking questions, predicting, observing, describing, measuring, classifying, making generalizations, inferring, and communicating.

b. [6-8] SA1.2 - The student demonstrates an understanding of the processes of science by collaborating to design and conduct simple repeatable investigations.

2. Concepts of Life Science:a. [6-8] SC3.1 – The student demonstrates an understanding that all organisms are linked to each other and their physical environments through the transfer and transformation of matter and energy by recognizing that organisms can cause physical and chemical changes (e.g. digestion, growth, respiration, photosynthesis) to matter and recognizing the importance of energy transfer in these changes.

Required Background1. A thorough understanding of cellular respiration in both aerobic and anaerobic conditions would be helpful for setting the experimental context and answering student questions (see a basic biology textbook such as Campbell and Reece).

Vocabulary1. Aerobic2. Anaerobic3. Fermentation4. Respiration5. Carbon dioxide6. Kingdom fungi7. Yeast8. Independent variable9. Dependent variable

MaterialsSupplies: Activities 1 and 2 – per group1. Water kettle2. Funnel3. Thermometer4. Ruler5. Scale (grams, if available)6. Spoons7. Bottles (clear, same sizes) - 5 per group8. Small cups - 5 per group9. Large cups - 5 per group10. Graph paper11. Sugar (80 g)12. Yeast (60 g)13. Stop watch

Additional Supplies: Activity 21. Honey2. Splenda®

3. Brown sugar4. Corn starch5. Vinegar6. White sugar7. Corn Syrup 8. Any other sugar sources available

Activity Preparation and ProcedureGeneral Guidelines1) These activities are designed to be completed over two separate hour-long sessions. Groups should be no larger than 4 students each.

2) Yeast can become costly so if funds are limited, choose narrower or smaller bottles and reduce the amount of sugar and yeast needed while maintaining the 3:4 yeast to sugar ratio in activity one.

3) The ratio (15g yeast: 20g sugar) reported in this packet is designed for clear liter soda bottles. Do not use bottles smaller than 20oz because the height of the foam can be compromised by a lack of volume.

4) If time runs short, ask the students to stop taking measurements at 15minutes.

5) Dividing up the labor among groups is useful, but remind students that the water must be prepared last.

6) If using honey, corn syrup or something sticky in activity two, ask the students to mix the sticky food with the water and then funnel it into the bottles.

Session 1 - Activity One1) Pass out one packet for each student.2) Ask your students if they have ever made bread. Ask them to describe the ingredients in bread. What

makes bread rise? Tell the students that they will find out in a fun experiment with a member of Kingdom Fungi: yeast! (5 minutes)

3) Introduce the concept of respiration. (5 minutes)a. All living cells respireb. Once food is eaten, or created in the case of plants, it needs to be broken down into more

manageable products for cells to harness energy for lifec. Respiration is essential for vital cell processes such as growth, reproduction etc.

4) Explain that the first activity is described in their packets. While they wait to take measurements, there are questions to answer in the packet.

5) Describe rules and suggestions by providing a quick demo of the basic setup. (3 minutes)6) Tell the students to get started with the guided experiment. The instructor may wish to walk younger

students through each step. (35 minutes)7) Provide instruction that they are to graph, analyze and draw conclusions with their data in class or at

home.

Example Setup for Activity 1:

Session 2 - Activity Two1) Ask students to revisit their yeast and respiration experiment packets. 2) Review the basic concepts learned from their first experiment: (10 minutes)

a. What is respiration?b. How does yeast obtain sugar for respiration?c. What was the conclusion from experiment one?d. How could you have improved experiment one?

3) Present the food options for the new experiment. 4) Ask students to design their new experiment within their groups. (15 minutes)5) Once each group has agreed upon a design and had it checked off by an instructor, let the experimenting

begin! (30 minutes) 6) Provide instruction that they are to graph, analyze and draw conclusions with their data in class or at

home.

Example Setup for Activity 2:

AssessmentTeacher’s key to student work packetThinking About Respiration

1. What are the end products of photosynthesis? Glucose and Oxygen

2. What substance from photosynthesis do cells use to respire? (Do you see the connection!?) Glucose and oxygen

3. Why do cells respire? (What product of respiration is useful to the cell?) Cells respire to obtain usable energy for life processes within the cell.

4. Why do you think we use yeast to make bread? Explain. I think we use yeast to make bread because it makes the bread rise. This happens because the yeast

cells respire and therefore produce carbon dioxide. The carbon dioxide creats bubbles in the bread dough and consequently make the dough rise.

5. Why do you think we use yeast to make wine? Yeast is used to make wine because without the presence of oxygen, respiration is called

fermentation. Fermentation creates new waste products including alcohol.

Thinking Through the Scientific Process6. In this experiment, why would measuring the height of the foam (bubbles full of a particular gas) tell us

about yeast’s respiration rates? Explain. Carbon dioxide is a product of respiration. The bubbles in the foam are full of the carbon dioxide

created by the yeast’s respiration. By comparing the heights of the foam, we can conclude the relative rates of respiration for our five treatments: 20°C, 30°C, 40°C, 50°C, 60°C.

7. What is the research question for this experiment? How does temperature affect rates of yeast respiration?

8. The independent variable (manipulated variable) for an experiment is the factor that you change on purpose in an experiment. What is the independent variable for your experiment?

Temperature9. The dependent variable (responding variable) is the variable that may change as a result of a change in

the independent variable. The dependent variable is the data that is observed and measured in an experiment. What is the dependent variable for this experiment?

Rate of respiration (foam height)10. In a controlled experiment (fair test) all other factors should be kept the same so that you can fairly

compare the results from the control group and the experimental group. List three controlled variables - factors that were kept constant in both of the setups for this experiment.

Amount of yeast and sugar; bottle size, room temperature, amount of water, etc.

Results and Analysis1. Once your data is collected, use graph paper to create a graph that clearly shows your results.

Line graphs are recommended2. State one conclusion you can draw from your experiment.

This depends on the student’s results but ideally the conclusion will be that the 40°C water displayed the highest rates of respiration. There was an optimal temperature for yeast respiration: neither cold or hot water was best.

3. Do your results support your hypothesis? Why or why not? This depends on the student.

4. Describe two specific things that you could have done to improve the reliability of this experiment. Controlled the temperature of the water through time; measured amounts with more accuracy;

took measurements in a more timely manner, etc.

Activity #2: Design Your Own ExperimentDescribe your experimental design. What is your question? (Hint: Take the broad provided question, and make it more specific to the food types your group has decided to test.)

Example: Will Splenda® , brown sugar, or vinegar result in the highest rate of yeast respiration?

What are the independent and dependent variables? Independent: food type. Dependent: rate of respiration (height of foam).

How will you collect data? Example: I will measure height of foam every 5 minutes for 15 minutes total.

1. If you were trying to answer this question in the best way possible, would you only do this experiment once? Explain.

I would repeat this experiment at least 3 times, or as many times as possible to make a conclusion. I would do this to account for errors each time I did the experiment, to make sure that I am making accurate conclusions. In scientific work, repeating experiments provides more reliability and confidence in your results.

Complementary Activities and Extension Ideas1. Ask students write a brief report about their experiments and present it to the class.

2. In addition, students may create a poster about their experiments and set up a poster sharing session as if they were at a scientific conference.

ReferencesCampbell, N.A. and Reece, J.B. (2008) Biology, 8th ed. San Francisco, CA: Pearson Education, Inc.

Available at the UAF BioSciences Library, call no: QH308.2.C34 2008

Science Take Out (2012) Yeast Respiration. Retrieved Nov. 5 2012 from sciencetakeout.com

Hands on Kingdom Fungus: Yeast and Respiration Experiments

To obtain energy for life, all cells must carry out a process called respiration. You will be exploring respiration using a member of Kingdom Fungi: yeast. Kingdom Fungi is incredibly diverse. Today, we will explore one of its smallest members: yeast are microscopic organisms that may be used to model respiration rates in more complex living organisms.

Activity #1: Guided Experimentation Research Question: How does temperature affect yeast respiration?Your hypothesis:

Test your hypothesis: 1. Label each of the 5 bottles provided to your group.2. Measure 15 grams of yeast into each cup.3. Measure 20 grams of sugar into each cup.4. Mix yeast + sugar. You should now have 5 yeast and sugar mixtures. 5. Use a funnel to pour one yeast + sugar mixture into each of the 5 bottles. 6. Heat water in kettle provided. 7. Using the provided thermometers, measure out one cup of water at 20°C, 30°C, 40°C, 50°C, and 60°C.8. Once all five cups of water are about the right temperature, use the funnel to add them to each of the five

bottles. 9. Immediately start your timer.

Data Collection1. Make initial observations and write them down. 2. Every 5 minutes measure the foam that develops on top of the water in centimeters.3. Stop measurements at 20 minutes.

Time (Minutes)

Height of Foam in Centimeters

20°C 30°C 40°C 50°C 60°C

Start

5

10

15

20

Thinking About Respiration: Essentially all living things require basic sugars to carry out respiration. Respiration creates energy for cells to carry out important functions. For example, fungi cannot photosynthesize (make sugars using energy from sunlight). Instead, they consume other organisms to get sugar for respiration. Whether eaten or created through photosynthesis, these sugars are broken down and turned into energy for cells! In the process, they

Assign one person to keep track of time.While you wait for measurements, answer questions 1-10.

produce waste products, including carbon dioxide gas, which the cells discard. Below, we will take a closer look at photosynthesis and respiration to become familiar with these processes!

Photosynthesis6 CO2  + 6 H2O → C6H12O6  + 6 O2

6 Carbon Dioxide + 6 Water → Glucose (sugar) + 6 Oxygen

Respiration with Oxygen (Aerobic)C6H12O6  + 6 O2  → 6 CO2  + 6 H2O + energy for cell

Glucose (sugar) + 6 Oxygen → 6 Carbon Dioxide + 6 Water + energy for cell

1. What are the end products of photosynthesis?

2. What substance from photosynthesis do cells use to respire? (Do you see the connection!?)

3. Why do cells respire? (What product of respiration is useful to the cell?)

When oxygen is not available, organisms may still carry out respiration to get energy for their cells. Respiration without oxygen is called fermentation. Fermentation results in a new waste product. Can you find it? Respiration without oxygen is what we will see yeast carry out today!

Respiration without Oxygen (Anaerobic)Sugar → Carbon Dioxide + Alcohol + energy

4. Why do you think we use yeast to make bread? Explain.

5. Why do you think we use yeast to make wine?

Thinking Through the Scientific Process6. In this experiment, why would measuring the height of the foam (bubbles full of a certain gas) tell us

about yeast’s respiration rates? Explain.

7. What is the research question for this experiment?

8. The independent variable (manipulated variable) for an experiment is the factor that you change on purpose in an experiment. What is the independent variable for your experiment?

9. The dependent variable (responding variable) is the variable that may change as a result of a change in the independent variable. The dependent variable is the data that is observed and measured in an experiment. What is the dependent variable for this experiment?

10. In a controlled experiment (fair test) all other factors should be kept the same so that you can fairly compare the results from the control group and the experimental group. List three controlled variables - factors that were kept constant in both of the setups for this experiment.

Results and Analysis1. Once your data is collected, use graph paper to create a graph that clearly shows your results.

2. State one conclusion you can draw from your experiment.

3. Do your results support your hypothesis? Why or why not?

4. Describe two specific things that you could have done to improve the reliability of this experiment.

Activity #2: Design Your Own ExperimentIn this activity you will design, conduct and report on an experiment to answer the following research question:

What type of food results in the highest rate of yeast respiration?

State your hypothesis:

Describe your experimental design.What is your question? (Hint: Take the broad provided question, and make it more specific to the food types your group has decided to test.)

What are the independent and dependent variables?

How will you collect data?

Construct a data table and record observations below.

Results and Analysis1. Once your data is collected, use graph paper to create a graph that clearly shows your results.

2. State one conclusion you can draw from your experiment.

3. Do your results support your hypothesis? Why or why not?

4. Describe two specific things that you could have done to improve the reliability of this experiment.

5. If you were trying to answer this question in the best way possible, would you only do this experiment once? Explain.