UNIT 2 VERNIER PROBEWARE LAB (modified from Vernier Lab 31C, CIBT
Elodea Lab and McDougal Littell)
PHOTOSYNTHESIS AND RESPIRATION
BACKGROUND:
Plants make sugar, storing the energy of the sun into
chemical energy (glucose), by the process of
photosynthesis. When they require energy for their
metabolic processes, they can tap the stored energy in
sugar by a process called cellular respiration. Therefore,
plants can carry out both photosynthesis and respiration
simultaneously.
Class
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The process of photosynthesis involves the use of light energy to convert carbon dioxide and water into sugar, oxygen, and
other organic compounds. This process is often summarized by the following reaction:
6 H2O + 6 CO2 + light energy → C6H12O6 + 6 O2
Cellular respiration refers to the process of converting the chemical energy of organic molecules into a form immediately
usable by organisms. Glucose may be oxidized completely if sufficient oxygen is available by the following equation:
C6H12O6 + 6 O2 → 6 H2O + 6 CO2 + energy
All organisms, including plants and animals, respire all
the time to oxidize glucose for energy. Often, this energy
is used to convert ADP and phosphate into ATP. The
energy from ATP is used to synthesize molecules, move
materials around within the organism, grow (create new
cells) and reproduce. Notice that in photosynthesis,
CO2 (carbon dioxide) is being used up as it is “fixed” into
glucose molecules. During respiration the opposite is
true. As the plant releases the energy stored in glucose
by breaking it down, CO2 is being given off into the
surrounding water or atmosphere. The relationship
between these two processes is special in that it allows
plants to recycle some of their by-products. (While CO2
is being given off during respiration, it can be re-utilized
during photosynthesis
During Photosynthesis:
O2 is increasing/decreasing.
CO2 is increasing/decreasing.
PURPOSE:
In this lab, you will try to demonstrate the change in
oxygen and carbon dioxide when spinach leaves are
placed under different conditions. You will be using
chemical sensors (O2 and CO2) as a means of
determining the change in O2 and CO2.
During Respiration:
O2 is increasing/decreasing.
CO2 is increasing/decreasing.
PRELAB: Use the background to answer the following questions:
1. Draw the 1st diagram (front page) into your lab notebook and choose the correct responses in the boxes.
2. What is the goal of photosynthesis?
3. Write the balanced chemical equation for photosynthesis.
4. What happens to the concentrations of O2 and CO2 in a closed system during photosynthesis?
5. Who does photosynthesis?
6. What is the goal of respiration?
7. Write the balanced chemical equation for respiration.
8. What happens to the concentrations of O2 and CO2 during respiration?
9. Who does respiration?
OBJECTIVES:
In this experiment, you will
 Use an O2 Gas Sensor to measure the amount of oxygen gas consumed or produced by a plant during
respiration and photosynthesis.
 Use a CO2 Gas Sensor to measure the amount of carbon dioxide consumed or produced by a plant during
respiration and photosynthesis.
 Determine the rate of respiration and photosynthesis of a plant.
MATERIALS:
Computer (1)
Vernier computer interface(1)
Logger Pro® (1)
Vernier O2 Gas Sensor (1)
Vernier CO2 Gas Sensor (1)
BioChamber 2000 (1)
aluminum foil (2-2 foot sheets)
12-inch (32.5 cm) ring fluorescent
lamp (1)
adaptor set up (1)
spinach leaves (enough to line the
bottom of the chamber twice)
Day 1 PROCEDURE: Exploring Photosynthesis and Respiration using the BioChamber 2000 and Vernier Probes
IMPORTANT: DO NOT TURN THE LAMP ON UNTIL INSTRUCTED TO DO SO.
In the dark:
1) Cover the bottom of the chamber with one layer of fresh turgid spinach leaves. Remove any stems that could interfere
with an even lining of the bottom.
2) Secure the lid tightly on the chamber.
3) Wrap the BioChamber with aluminum foil so that no light will reach the leaves.
a) Wrap the outside of the chamber with foil.
b) Cover the lid with foil, poking the holes open to insert the sensors.
c) Wrap the bottom part of foil over the bottom part of the chamber and up over the lid so the entire chamber is
covered.
4) If your CO2 Gas Sensor has a switch, set it to the low (0-10,000 ppm) setting. Connect the CO2 Gas Sensor to Channel
1 and the O2 Gas to Channel 2 of the Vernier computer interface.
5) Click on the Logger Pro software that is located on the desktop of the computer.
6) Prepare the computer for data collection by opening the file "31C Photo (CO2 and O2)” in the Biology with Vernier
folder of Logger Pro.
7) Insert the sensors into the holes.
8) Make sure your Logger Pro® is plugged into power and into the computer. If the play button (right arrow) turns green,
you have done it correctly.
9) Wait 5 minutes for the sensors to equilibrate.
10) While you are waiting, set the data collection time to every 30 seconds. Go to the “experiment” tab, click on data
collection. Change the length to 15 minutes and the sample rate to 2 samples/minute.
11) After 5 minutes, click
to begin the 15-minute data collection.
12) If you are unable to see your data on the graph, click anywhere on that graph. Autoscale the data by clicking the
Autoscale button on the toolbar.
13) When data collection is complete, determine the rate of respiration.
a) Click anywhere on the CO2 graph. Autoscale the data again, by clicking the Autoscale button on the toolbar.
b) To make a best fit line, move the cursor to the point where the data values begin to increase. Hold down the left
mouse button. Drag the cursor to select the region of increasing CO2 gas concentration.
c) Click on the Linear Fit button to perform a linear regression (or click the “Analyze” and then linear fit). A box will
appear with the formula for a best fit line.
d) Record the slope of the line, m, as the rate of respiration in your data table. The units will be ppt/min (parts per
trillion/minute).
e) Close the linear regression box.
f) Repeat Steps 13 a-e for the O2 graph, selecting the region of decreasing O2 concentration.
14) Record your data onto your data table. Add a final row for the m for each gas.
15) Clean Up: Put the O2 sensor into the small plastic bottle and place back into the box RIGHT SIDE UP! Put the other
sensor in the appropriate box. Place the LabPro and appropriate cords in their box. Remove the aluminum foil and
throw out the spinach leaves. Shut down the computer.
16) Make a graph from this data (or use the one from the program to guide you).
In the light:
1. Locate the Lamp assembly. Do not turn the lamp on until instructed to do so.
2. Invert the chamber to remove the leaves and accumulated gases.
3. Line the bottom of the chamber with fresh turgid spinach leaves.
4. Secure the lid on the chamber and insert the sensors into the holes.
5. Place the chamber inside the bulb and plug in the cord to turn on the lamp.
6. Connect the CO2 Gas Sensor to Channel 1 and the O2 Gas to Channel 2 of the Vernier computer interface.
7. Click on the Logger Pro software that is located on the desktop of the computer.
8. Prepare the computer for data collection by opening the file "31C Photo (CO2 and O2)” in the Biology with Vernier
folder of Logger Pro.
9. Make sure your Logger Pro® is plugged into power and into the computer. If the play button (right arrow) turns green,
you have done it correctly.
10. Wait 5 minutes for the sensors to equilibrate.
11. While you are waiting, set the data collection time to every 30 seconds. Go to the “experiment” tab, click on data
collection. Change the length to 15 minutes and the sample rate to 2 samples/minute.
12. After 5 minutes, click
to begin the 15-minute data collection.
13. Record your data onto your data table.
14. Make a graph from this data (or use the one from the program to guide you).
15. Clean and dry the chamber.
DATA:
Create an appropriate data table that will include both the CO2 rate and O2 rate of production/consumption in ppt/min.
Follow all rules for making a data table.
GRAPHS:
Create two graphs, one comparing CO2 levels over time in the light and dark, and another comparing O2 levels over time in
the light and dark.
ANALYSIS:
In the dark
1. In the dark, was either of the rate values for CO2 a positive or negative number? If so, what process must be taking
place in the leaves in order for this to happen?
2. In the dark, was either of the rate values for O2 a positive or negative number? If so, what process must be taking place
in the leaves in order for this to happen?
3. Do you have evidence that cellular respiration occurred in leaves? Explain.
4. Do you have evidence that photosynthesis occurred in leaves? Explain.
5. Calculate the total change in O2 (final O2 minus initial O2).
6. Calculate the total change in CO2 (final CO2 minus initial O2).
7. Which one had the biggest change, O2 or CO2?
8. Using your answers from #5 and 6, what is the ratio of O2 to CO2? What is the relationship between O2 and CO2? Why
do you think the relationship is like this?
In the light
9. What is a validity measure for this part of the experiment?
10. In the light was either of the rate values for CO2 a positive or negative number? If so, what process must be taking place
in the leaves in order for this to happen?
11. In the light was either of the rate values for O2 a positive or negative number? If so, what process must be taking place
in the leaves in order for this to happen?
12. Calculate the total change in O2 (final O2 minus initial O2).
13. Calculate the total change in CO2 (final CO2 minus initial O2).
14. Which one had the biggest value, O2 or CO2?
15. Do you have evidence that cellular respiration occurred in leaves in the light? Explain (think about your calculations
from the previous questions).
16. Using your values from #12 and 13, what is the ratio of O2 to CO2? What is the relationship between O2 and CO2? Why
do you think the relationship is like this?
17. Compare question #5 and 6 with question #12 and 13. Is photosynthesis or respiration happening faster when the plant
is in the light? Explain using your calculations.
18. Do you have evidence that photosynthesis occurred in the leaves in the light? Explain.
19. List five factors that might influence the rate of oxygen production or consumption in leaves. Explain how you think each
will affect the rate.