AP Biology Laboratory 5 Respiration Virtual Student Guide

Transcription

1 Name: Date: AP Biology Laboratory 5 Respiration Virtual Student Guide PRE LAB QUESTIONS: Before you begin the online lab, log onto the Bozeman videos web page at and watch 2 videos under the AP Biology Labs section: AP Biology Labs #05 Cellular Respiration Cellular Respiration Lab Walkthrough PreLab: Bozeman AP Lab Video 05 Cellular Respiration: 1. What are the three stages of cellular respiration and where does each occur in the cell? 2. What are we really trying to do in this lab? 3. How will we do this (i.e. what will we measure specifically?) 4. What device is used to measure in this lab? 5. What are the important parts of this device? 6. What does KOH do in the presence of carbon dioxide? 7. What are the glass beads used for? 8. What should the final graph look like for this experiment with the peas? L. Carnes

2 PreLab: Bozeman AP Lab Cellular Respiration Lab Walkthrough: 1. How many germinating peas will be used? 2. What process will you use to determine the volume of materials to be used? 3. How do you make up for the difference in the size of the germinating and non-germinating peas? 4. What goes in to the VERY bottom of each respirometer (first thing to put in) and why? 5. What is the non-absorbent cotton for? 6. Explain the equilibration period for this experiment what is happening during this time and why are you doing this? Virtual Lab Now log onto the PH School web page at Select Lab 5: Cellular Respiration Complete the virtual lab activity and record your responses in this packet.

3 Introduction Cellular respiration occurs in most cells of both plants and animals. It takes place in the mitochondria, where energy from nutrients converts ADP to ATP. ATP is used for all cellular activities that require energy. In this laboratory, you will observe evidence for respiration in pea seeds and investigate the effect of temperature on the rate of respiration. Key Concepts The Raw Materials and Products of Respiration Choosing from the following list, type in the correct molecules to show raw materials and products in the equation for cellular respiration. More to Review In photosynthesis, plants convert light energy into chemical energy stored in sugars and other organic compounds. Cellular respiration, the process that uses the energy stored in these organic molecules to convert ADP to ATP, occurs in both plants and animals. In what ways are the processes of cell respiration and photosynthesis interdependent, or coupled? Draw a model that illustrates this interdependence.

4 The Process of Respiration We sometimes refer to our breathing as "respiration." Other organisms, including the cricket below, have different mechanisms for exchanging gases with the environment. Respiration at the Cellular Level Design of the Experiment How can the rate of cellular respiration be measured? When you study the equation for cellular respiration, you will see that there are at least three ways: 1. Measure the amount of glucose consumed. 2. Measure the amount of oxygen consumed. 3. Measure the amount of carbon dioxide produced. In this experiment, we are going to measure the amount of oxygen consumed.

5 Features and Functions of a Respirometer This illustration shows you the basic features of a respirometer. It will measure changes in gas volume related to the consumption of oxygen. You can construct a respirometer by putting any small organism in a vial with a pipette attached. This example uses a cricket; in the laboratory experiment, you will use peas. Remember, cellular respiration occurs in the cells of both animals and plants! How the Respirometer Works When the tip of the respirometer is submerged, no additional air will enter. The CO 2 that is produced combines with KOH to form a solid precipitate, K 2 CO 3. Notice that as the gas volume inside the vial decreases, the pressure of water outside the vial forces water into the pipette. Because the amount of water that enters the pipette is directly proportional to the amount of oxygen consumed by the cricket, measuring the water volume in the pipette allows you to measure the rate of respiration. How to Read a Pipette Water in a pipette adheres to the side of the tube and forms a curved surface called a meniscus. By common practice, all readings are made at the bottom of the meniscus. The units for this pipette are milliliters (ml).

6 Assembling the Respirometer In this experiment you will compare the rate of respiration in peas that are germinating to the rate in peas that are dormant (dry peas). You will make the comparison at two different temperatures: 10 C and 25 C. In addition, you will compare these rates to a nonmetabolizing control. Why is it important to have a control? The following illustration shows you how to assemble a respirometer. It is important that the three vials contain an equal volume of contents. You do this by adding glass beads to the vial with the dormant peas, since the dry peas take up less space than an equal quantity of germinating peas. Note: Because you are measuring the rate of respiration at two different temperatures, prepare two sets of three vials. Lab Hints 1. You will need to use a layer of nonabsorbent cotton between the KOH and the peas. 2. The stopper must be firmly inserted for an air-tight seal. Check that no peas or beads block the opening to the pipette. 3. Let the respirometers equilibrate for several minutes in their respective waterbaths. This will minimize volume changes due to change in air temperature. More Information on Germinating Peas Seeds contain a plant embryo and its initial food supply protected by a seed coat. When warmth and moisture conditions are favorable, germination, or sprouting, will begin. When you soak pea seeds for this laboratory, germination begins. Enzymes begin using the stored food supply to generate ATP, and the rate of cellular respiration accelerates. It is important to know that nongerminating seeds are not dead; they are dormant. Do they respire?

7 Measuring the Rate of Respiration Gas volume is related to the temperature of the gas. According to the gas law (V=nRT/P), a change in temperature will cause a direct change in volume. Because the temperature in the respirometers may vary during the course of the experiment, you must correct for differences in volume that are due to temperature fluctuation rather than rate of respiration. To do this, subtract any difference in the movement of water into the vial with glass beads from the experimental vials held at the same temperature. Record the result as the corrected difference. Analysis of Results I After you have collected data for the amount of oxygen consumed over time by germinating and nongerminating peas at two different temperatures, you can compare the rates of respiration. Let's review how to calculate rate. Rate = slope of the line, or In this case, Δy is the change in volume, and Δx is the change in time (10 min).

8 Lab Quiz 1. Which of the following is a TRUE statement based on the data? a. The amount of oxygen consumed by germinating corn at 22 C is approximately twice the amount of oxygen consumed by germinating corn at 12 C. b. The rate of oxygen consumption is the same in both germinating and nongerminating corn during the initial time period from 0 to 5 minutes. c. The rate of oxygen consumption in the germinating corn at 12 C at 10 minutes is 0.4 ml O 2 /minute. d. The rate of oxygen consumption is higher for nongerminating corn at 12 C than at 22 C. e. If the experiment were run for 30 minutes, the rate of oxygen consumption would decrease. 2. What is the rate of oxygen consumption in germinating corn at 12 C? a ml/min. b ml/min. c. 0.8 ml/min. d. 0.8 ml/min. e ml/min.

9 3. Which of the following conclusions is supported by the data? a. The rate of respiration is higher in nongerminating seeds than in germinating seeds. b. Nongerminating peas are not alive, and show no difference in rate of respiration at different temperature. c. The rate of respiration in the germinating seeds would have been higher if the experiment were conducted in sunlight. d. The rate of respiration increases as the temperature increases in both germinating and nongerminating seeds. e. The amount of oxygen consumed could be increased if pea seeds were substituted for corn seeds. 4. What is the role of KOH in this experiment? a. It serves as an electron donor to promote cellular respiration. b. As KOH breaks down, the oxygen needed for cellular respiration is released. c. It serves as a temporary energy source for the respiring organism. d. It binds with carbon dioxide to form a solid, preventing CO2 production from affecting gas volume e. Its attraction for water will cause water to enter the respirometer. Conclusion Essay Prompt The results below are measurements of cumulative oxygen consumption by germinating and dry seeds. Gas volume measurements were corrected for changes in temperature and pressure. a. Using the graph paper provided, plot the results for the germinating seeds at 22ºC and at 10ºC. b. Calculate the rate of oxygen consumption for the germinating seeds at 22ºC, using the time interval between 10 and 20 minutes. c. Account for the differences in oxygen consumption observed between: i. germinating seeds at 22 C and at 10 C ii. germinating seeds and dry seeds d. Describe the essential features of an experimental apparatus that could be used to measure oxygen consumption by a small organism. Explain why each of these features is necessary.

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