Dry Lab: Cellular Respiration

A dry lab is when you learn about a lab experiment without actually performing the experiment yourself. Today you will explore a lab that tests the effect of temperature on a germinating pea’s ability to do cellular respiration. Upon completing this dry lab, you should be able to understand:

  • What a null hypothesis is and how to apply it to this experiment.
  • How the rate of cellular respiration can be measured by a respirometer
  • The relationship between volume, pressure, and temperature in a closed system.
  • The importance of controls and only measuring one variable at a time in an experiment.

Note: You will be working as a group to understand the lab and analyze data, but all work in your lab notebook should be your own—you should not copy phrases or diagrams from others or from the materials that you are being provided with.

Step 1: Background Information/Hypothesis

  1. Read through the Background Information. Discuss it with your lab group so that you can answer the following questions:
  2. What are some ways that you could measure cellular respiration in an organism?Which gas will you be measuring in this experiment?
  3. What is the relationship between moles of a gas and the pressure in that system?
  4. When the volume of gas changes in system, how will the pressure exerted by this gas change as well (assuming other variables remain constant)?
  5. In terms of pressure, what direction will both gases and fluids flow in (high to low or low to high)?
  6. After you all feel comfortable with this lab, you should move on to forming a hypothesis. The purpose of this lab is to measure the effect of temperature on a germinating pea’s rate of cellular respiration. As a lab group, you will need to form a hypothesis about what will happen to the rate of cellular respiration at different temperatures (10C and 25C). Write an appropriate title and intro for this lab in your lab notebook. Include your hypothesis in your introduction.
  7. NOTE: Since this is a dry lab, your title should start with “Dry Lab” followed by a more specific title. (Ex: Dry Lab: Determining if Alu is present in the PV92 region)
  8. A null hypothesis is defined as a statement that is assumed to be true until it is disproven. Usually, in the context of an experiment, the null hypothesis is that there will be no difference between the groups being compared in the experiment.
  9. What would the null hypothesis be for this experiment? Note this in your introduction as well.

Step 2: Understanding the Procedure

  1. In the next few steps, you will become more familiar with respirometers and how to use them to conduct a controlled experiment. Carry out each of the steps in order to better understand the procedure and the equipment used.
  2. In a controlled experiment, there should only one variable, which means you will need to take steps to eliminate other variables. The respirometer is a closed system in which you will be able to account for and eliminate some of these variables.

(A)Volume

Pressure of a gas will be affected by the volume that the gas is found in. You need to make sure the total volume of the organisms in each respirometer is the same so that the same volume is available for the gases being measured in this experiment. Volume can be measured by determining the amount of water that is displaced by the organism (in this case, peas).

I. Locate the graduated cylinder with peas in it at Station 1. The peas were added to 25 mL of water. Based on the amount of water displaced, estimate the volume of the peas. Jot this number down on the left side page of the your lab notebook.

II. In another respirometer, you will need to use glass beads instead of peas. Using the materials in your lab set up, fill your graduated cylinder with 25 mL of water and add glass beads until the water displaced is equivalent to the volume of the peas. Note the number of glass beads in the water.

III. Dry off the glass beads and put them back in the canister.

(B) KOH

KOH is another component that you will be adding to each respirometer. Read through the Background Information, and discuss what the following questions:

  • What reaction will the KOH participate in?
  • Why is it necessary to add KOH to the respirometer?

(C) Temperature

Water baths will be used to maintain a constant temperature throughout the experiment. There will be 2 temperatures tested—10 C and 25 C. Before you actually start taking readings (collecting data), you will need to equilibrate the respirometers in the water bath to get it to the correct temperature.

  • Go to Station 2 to observe a respirometer that is being equilibrated.
  • Discuss the following question with your lab group: Why is it important to equilibrate the respirometers before beginning to collect data? What effect would this have on your data?

(D) Pressure

This is what you will indirectly be measuring in this experiment—you will be measuring the change in the pressure due to O2 gas.

I. Discuss the following questions with your lab group.

  • How will the pressure of the O2 change as the peas go through cellular respiration?
  • Since oxygen is a colorless gas, how will you see any changes in the amount of/pressure from O2?
  • What will you observe right after you put the respirometer into the water (after equilibration)?
  • What will you observe in the respirometer as the experiment progresses?

II. Locate Station 3 and observe the respirometers. Note the time that has elapsed on the timer and take the readings for each of the respirometers. Record this on the data sheet next to the lab set up.

  1. Read through the Procedure in more detail.
  2. Put the laminated procedure cards in the correct order according to the procedure. Make sure you know what the purpose of each step is.
  1. Draw a flow chart of the procedure in your lab notebook.
  • You can use the laminated cards as a guide but your flowchart should also include diagrams of the set up/equipment and other additional information. You do NOT need to write down every step— the goal is to understand the main idea of each major step.
  1. Show your flowchart to your teacher to receive a stamp. You will need to answer questions to show you understand the procedure and purpose of this lab. At this time, your teacher will also give you sample data to analyze and conclusion questions to answer.

Step 3: Data Analysis and Conclusions

  1. Paste the sample results into your lab notebook under the heading “Sample Results”. You do not need to have anyone confirm these results in your notebook.
  2. Take some time to look over these results to make sure you understand what the numbers mean. You should be able to answer the following questions:
  • What do the headings in the table mean? What do you have to subtract from what? Why do you subtract them?
  • Using the data, how many mL of O2 is consumed by the germinating peas at 25C after 15 minutes?
  • Nongerminating peas are pea seeds that are still dormant. These serve as another control for the experiment. What is the other control for this experiment?
  1. Graph the data for the mL of O2 consumed by the germinating peas at 10 C and 25C over the course of 20 minutes. Make sure you label your axes properly and label the two lines (for the different temperatures). Paste your graph into your lab notebook and write an appropriate title and caption for this graph. This will be Figure 2.
  1. Paste the conclusion questions into your lab notebook and answer them. Conclusion questions can be discussed with your lab partners but make sure you write your answers in your own words!

** Don’t forget to date every page and to put this lab into your table of contents! **

Conclusion questions:

  1. Based on the data, describe and explain the relationship between the amount of O2 consumed and time.
  1. What will happen if you forget to put KOH in the respirometer? Be specific about how it will affect

your data collection.

  1. Why did the vial have to be completely sealed around the stopper?
  1. Why is it necessary to correct the readings from the peas from the readings from the beads?

5. If you used the same experimental design to compare the rates of respiration of a 25 g reptile and a

25 g mammal at 10 oC, what results would you expect? Explain your reasoning.

6. If respiration in a small mammal were studied at both room temperature (25 oC) and 10 oC, what results

would you predict? Explain your reasoning.