Name:___________________________________ Date:___________ Period:_______
Photosynthesis and Cellular Respiration Using the GLX
Today you will be conducting an experiment using a plant. First you will examine photosynthesis and then
cellular respiration. Then you will design and carry out your own experiment.
Do it now!
Write the equation in both words and molecular formulas for photosynthesis and cellular respiration in the
space provided below.
Photosynthesis:
Cellular Respiration:
Hypothesis: If a plant is exposed to sunlight and the amount of carbon dioxide is determined, then the
amount of carbon dioxide will _______________________.
If the same plant is exposed to darkness and the amount of carbon dioxide is determined, then the amount of
carbon dioxide will _______________________________.
Materials: GLX, Carbon dioxide probe, mint plant, timer
Procedure:
1. Attach the carbon dioxide probe to the GLX and then turn the GLX on. Wait about 2 minutes for the
carbon dioxide probe to stabilize. Keep in mind that the probe is extremely sensitive and will
continually fluctuate. Also, the probe is very sensitive to rise in temperature. Be sure to keep the probe
from being affected by the heat of the lamp.
2. Carefully tease apart one plant from the bunch and rinse the roots with water. Add a small amount of
water to the plastic bottle to keep the roots moist while they are in the container during the experiment.
3. Gently place the plant into the bottle that you will find in the plastic container with the carbon dioxide
detector.
4. Place the probe into the bottle using the rubber adaptor. Wait about two minutes until the amount of
carbon dioxide remains fairly constant.
5. Obtain a lamp and plug it in. Check that the bulb is fluorescent. Place the bottle with the plant in front
of the lamp. Be sure to locate the light in such a manner as it is shining on the plant and not heating up
the plastic container or the probe. You may want to place a beaker of water between the light and the
plastic container with you plant as a heat sink.
6. Record the initial carbon dioxide level in ppm on the data table where it indicate light at time 0. Record
the level of carbon dioxide after every two minutes for a total of 10 minutes.
7. Cover the bottle with aluminum foil. Wait about a minute or 2 and record an initial carbon dioxide
reading in ppm. Record the carbon dioxide level in two minute intervals for a total of 10 minutes.
8. DO NOT WASTE TIME! During the 2 minute wait time, between readings, begin working on
answering the questions on a separate piece of paper. You may discuss your answers with your partners,
but DO NOT COPY. The answers to these questions are due at the end of the lab period.
9. Cleaning up instructions – Return all GLX, probes, plastic bottles and lids to their original location in
the classroom. Flatten out the foil and place it below the aluminum foil box. Return the plant to its
original container and leave the bottle on its side at your lab station.
Data:
Light data
Dark data
Time
ppm carbon dioxide
Time
ppm carbon dioxide
0
0
2
2
4
4
6
6
8
8
10
10
Graph you data below. Use color and or labels to indicate which portion of the graph shows the carbon
dioxide levels in the light and which portion shows the carbon dioxide levels in the dark.
Independent variable =
Dependent variable =
Title:___________________________________
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Analysis:
Calculate the rate of change in the light and in the dark. Rate = change in ppm carbon dioxide/ change in
time.
Light:
Initial – Final ppm =
Initial – Final time
_____________ ppm/minute
Dark:
Initial – Final ppm =
Initial – Final time
_____________ ppm/minute
Questions:
These questions must be answered in complete sentences in your notebook in order to receive credit!
Each question is worth 5 points.
1. Describe the overall change in carbon dioxide level during the time that the plant was exposed to light.
2. What process do you think occurs in mint plants exposed to the light that causes this change?
3. If you had a very sensitive scale, how do you suspect that the mass would change as photosynthesis
takes place? Explain your answer.
4. Why does the amount of carbon dioxide decrease when a plant is exposed to light?
5. Describe the overall change in carbon dioxide level during the time that the plant was exposed to
darkness.
6. Why does the amount of carbon dioxide in increase when the plant is exposed to darkness?
7. If you had a very sensitive scale, how do you think that the mass of the plant would change over time in
the darkness? Explain your answer.
8. What organisms are able to perform photosynthesis?
9. Which organisms perform cellular respiration?
10. How do you think an animal such as a cricket would react to the same environmental conditions as used
in this experiment? Would the amount of carbon dioxide rise or lower during light and dark exposure?
Explain your answer.
Independent Experiment:
Now it’s your turn to develop an experiment. Using the equipment provided, develop a procedure that will
test the affect of a variable on photosynthetic rate and or the rate of respiration. You may some or all of the
following materials: GLX, temperature probe, Carbon dioxide probe, plastic containers, ice, plants,
crickets, parafilm, lamps and any other materials available in the room. Please don’t be afraid to ask if a
material is available.
Part one – Establish the Problem and develop a hypothesis(10)
Identify what question you would like to answer such as: How will temperature affect the rate of respiration
in a cricket?
Problem
Hypothesis
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Part two – Identify the variables and the control(15)
Independent variable:
Dependent variable:
Control and variable: (Describe one or more controls that will be used in this experiment and what variable
you are testing in this experiment.)
Part three – Write a detailed Procedure(10 for words and 10 for performance)
On a piece of scrap paper work together and write up a brief outline of the procedure and show the
instructor. Once your experiment has been approved, each student should write a detailed procedure.
Part four – Collect Data(10)
Each student will need to create a data table and record data.
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Part Five – Graph(10) Each student will need to graph their data.
Part Six – Analysis(15)
Each student will discuss their hypothesis and whether or not their data supported it. Specific reference
should be made to graphs and data. Never use the wording “proves my hypothesis correct…” Your
hypothesis is supported or not supported by the data. One experiment is not proof!
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Part Seven – Conclusion(15)
Each student will discuss the methodology used in this experiment and suggest improvements and ideas for
further exploration.
Part 8 – Give your experiment a title!(5)
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