Learning Objectives

After completing this laboratory exercise, you should be able to:

1. Explain the role of cellular respiration in ATP production.
2. Measure oxygen consumption as evidence of cellular respiration.
3. Compare respiration rates in germinating and non-germinating beans.
4. Investigate how different sugars affect yeast respiration.
5. Explain how enzyme specificity influences substrate utilization.
6. Analyze and interpret respiration data using graphs and trendlines.
7. Calculate respiration rates using the slope of an oxygen-consumption graph.

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Key Terms

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Introduction

Cellular respiration is the process by which cells convert the chemical energy stored in food molecules into ATP, the usable energy currency of the cell.

The overall equation for aerobic cellular respiration is:

$$C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + ATP$$
During cellular respiration:

• Oxygen is consumed.
• Carbon dioxide is produced.
• Energy is released and stored as ATP.

In this laboratory you will investigate cellular respiration using two biological systems:

1. Germinating and non-germinating beans
2. Yeast supplied with different sugars

In Experiment 1, oxygen consumption will be measured directly using Vernier oxygen sensors.

In Experiment 2, methylene blue will be used as a redox indicator to compare respiratory activity in yeast supplied with different sugar sources.

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Materials

Experiment 1

• Vernier O₂ Gas Sensor
• LabQuest
• Respiration bottle/chamber
• Germinating beans
• Dry (non-germinating) beans
• Paper towels

Experiment 2

• Yeast suspension
• Glucose solution
• Fructose solution
• Sucrose solution
• Lactose solution
• Distilled water
• Methylene blue solution
• Test tubes
• Test tube rack
• Marker
• Water bath (37°C)
• Pipettes

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Experiment 1: Oxygen Consumption by Germinating Beans

Purpose

Determine whether germinating beans respire at a higher rate than non-germinating beans.

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Background

Germinating seeds are actively growing and require ATP for cellular processes. Therefore, they consume oxygen at a higher rate than dormant seeds.

As cellular respiration occurs, oxygen concentration inside the respiration chamber decreases.

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Procedure

Part A: Germinating Beans

1. Connect the O₂ Gas Sensor to the LabQuest.
2. Obtain approximately 25 germinating beans.
3. Gently blot the beans dry.
4. Place the beans into the respiration chamber.
5. Seal the chamber with the O₂ sensor.
6. Begin data collection.
7. Collect oxygen data for 10 minutes.
8. Record oxygen concentration every minute in Table 1.
9. Save the graph.

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Part B: Dry Beans

1. Remove the germinating beans.
2. Place approximately 25 dry beans into the chamber.
3. Seal the chamber with the O₂ sensor.
4. Collect oxygen data for 10 minutes.
5. Record oxygen concentration every minute in Table 1.
6. Save the graph.

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Table 1. Oxygen Concentration Data

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Excel Graph Instructions

Step 1

Enter your data into Excel using the following format:

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Step 2

Highlight all data.

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Step 3

Select:

Insert → Scatter Plot → Scatter with Straight Lines

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Step 4

Format the graph:

Title: Cellular Respiration in Beans

X-axis: Time (minutes)

Y-axis: Oxygen Concentration (%)

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Step 5

Add a trendline for each data series.

For each line:

1. Right-click the data series.
2. Select Add Trendline.
3. Choose Linear Trendline.
4. Check:
   • Display Equation on Chart
   • Display R² Value on Chart

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Table 2. Respiration Rate Calculations

Record the trendline equations from Excel.

Note: The slope represents the respiration rate.

A more negative slope indicates faster oxygen consumption and therefore a higher rate of cellular respiration.

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Experiment 2: Effect of Sugar Type on Yeast Respiration

Purpose

Determine which sugars can be utilized most effectively by yeast.

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Background

Yeast can metabolize some sugars more effectively than others.

During cellular respiration and fermentation, electrons are transferred through metabolic pathways. Methylene blue acts as a redox indicator.

• Oxidized methylene blue = blue
• Reduced methylene blue = colorless

Greater loss of blue color indicates greater respiratory activity.

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Procedure

Tube Setup

Label five test tubes:

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Add Solutions

To each test tube add:

• 5 mL yeast suspension
• 5 mL corresponding sugar solution

For Tube W add:

• 5 mL yeast suspension
• 5 mL distilled water

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Add Indicator

Add:

• 3 drops methylene blue

to each tube.

Mix gently.

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Incubation

1. Place all tubes in a 37°C water bath.
2. Incubate for 20 minutes.
3. Do not disturb the tubes during incubation.

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Evaluation

After 20 minutes compare the color of each tube.

Assign a color score using Table 3.

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Table 3. Methylene Blue Color Scale

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Table 4. Yeast Respiration Results

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Excel Graph Instructions

Create a bar graph using your data from Table 4.

Step 1

Enter the data:

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Step 2

Highlight the data.

Step 3

Select:

Insert → Column Chart

Step 4

Format the graph.

Title: Effect of Sugar Type on Yeast Respiration

X-axis: Sugar Type

Y-axis: Color Score

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Analysis Questions

1. What evidence indicated that cellular respiration occurred in germinating beans?
2. Which bean treatment had the steepest negative slope? What does this indicate?
3. Why did germinating beans consume oxygen faster than dry beans?
4. How is oxygen consumption related to ATP production?
5. Why is oxygen considered a reactant in aerobic respiration?
6. What is the significance of the slope of the oxygen graph?
7. Why was the water treatment included in Experiment 2?
8. What is the purpose of methylene blue in this experiment?
9. What does a low color score indicate about respiratory activity?
10. Which sugar appeared to support the highest rate of respiration?
11. Which sugar appeared to support the lowest rate of respiration?