Name_______________________ Period______
The Effect of (Carbon Dioxide) CO2 Concentration
on the Rate of Photosynthesis
Carbon dioxide, water, chlorophyll, and light are all needed for the photosynthetic reaction to take place
(Equation 1). If any of these are absent, glucose and oxygen will not be formed. If any are scarce, the products
may be formed slowly. The purpose of this lab is to measure the effect of CO2 concentration on
photosynthesis.
Equation 1
6CO2 + 6H2O + Light Energy → C6H12O6 + 6O2
We can monitor the photosynthesis reaction by measuring appearance of products. Oxygen gas (O2) is not
very soluble in water, so when photosynthesis occurs under water, bubbles of O2 form. Many times, the O2
bubbles get stuck in leaves and when enough O2 gets trapped in the leaves, the leaves begin to float. The
faster that leaves begin to float, that means that photosynthesis is happening quicker in those leaves.
Materials
Baking soda
Worksheet
Plastic syringes
Spinach leaves
Hole punch
2 clear cups
Timer
Light source
Procedure (for CO2 Concentration)
1. Make a 0.2% Sodium Bicarbonate solution by mixing 150 ml of water with 1 gram of baking soda. The
bicarbonate will serve as a source of carbon dioxide for the leaf disks while they are in the solution.
2. Pour the bicarbonate solution into a clear cup to a depth of about 3-4 inches. Label this cup “With CO2.” Fill a
second cup with only water to be used as a control group. Label this cup “Without CO 2.”
3. Using a hole punch, punch out 20 uniform leaf disks - 10 for each cup. Avoid major leaf veins.
4. Adding the leaf discs to the syringe, add “With CO2” solution to the syringe, plug the hole with your thumb, and
create a vacuum so that all leaves sink to the bottom of the syringe.
5. Do the same with 10 more leaf discs, except use “Without CO2” solution this time.
6. Place both cups under the light source and start the timer. At the end of each minute, record the number of
floating disks. Then swirl the disks to dislodge any that stuck against the side of the cups. Continue until the 10
minutes are up.
Data Table
Minute
High CO2 Concentration
Low CO2 Concentration
High CO2 Concentration
Low CO2 Concentration
1
2
3
4
5
6
7
8
9
10
Estimate how many will be
floating at 10 minutes
How many were actually floating
at 10 minutes
Discussion Questions
1. Which cup exhibited a faster rate of photosynthesis? High concentration of CO2 or low concentration of
CO2?
2. What data support this?
3. What effect did CO2 concentration have on the rate of photosynthesis?
4. What errors could have occurred during this lab?
5. What is another lab we could create using the same materials to measure the rate of photosynthesis?
6. Create Line Graph in your notebook using your data.
Answer these questions in your notebook 
Discussion Questions
7. Which cup exhibited a faster rate of photosynthesis? High concentration of CO2 or low concentration of
CO2?
8. What data support this?
9. So, what effect did CO2 concentration have on the rate of photosynthesis?
THE EFFECT OF_________________ ON __________________
Use the bulleted information below to help you compose a formal lab report. Keep in mind that you are still
required to meet all of the same objectives as before in this lab report and any future lab reports.
Introduction
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●
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Describe photosynthesis in a sentence
Include the photosynthesis equation
Identify the reactants of the photosynthesis equation
Identify the products of the photosynthesis equation
Explain why we count oxygen bubbles to measure photosynthesis
Explain what happens when enough bubbles get trapped in underwater leaves
Describe how we change light intensity and CO2 concentration
Results
●
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Report the ET50 values of each cup
Report the 1/ET50 values of each cup
Figures
● One graph for each cup plotting raw data - this is used to determine ET50 values
● One bar graph plotting 1/ET50 values for both cups
Conclusion
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●
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Answer all appropriate discussion questions first.
Then evaluate your hypothesis.
After that, discuss why your data may have been faulty.
Finally, discuss what new questions you might be interested to study now that you know how these
factors affect the rate of photosynthesis.
1. The Effect of Light Intensity on the Rate of Photosynthesis
Procedure (for Light Intensity)
1. Make a 0.2% Sodium Bicarbonate solution by mixing 300 ml of water with 1 teaspoon of sodium bicarbonate. The
bicarbonate will serve as a source of carbon dioxide for the leaf disks while they are in the solution.
3. Using a hole punch, punch out 20 or more uniform leaf disks - 10 for each cup. Avoid major leaf veins.
4. Add 10 leaf discs to a syringe, then add the CO2 solution to the syringe, plug the hole with your thumb, and create
a vacuum so that all leafs sink to the bottom of the syringe. Pour these 10 leaf discs in a cup labeled “High Light
Intensity”.
5. Do the same with 10 more leaf discs. Pour these 10 leaf discs in a cup labeled “Low Light Intensity”.
7. Place the HLI cup as close to the light source as possible. Place the LLI cup 30 cm behind the first cup.
8. At the end of each minute, record the number of floating disks. Then swirl the disks to dislodge any that stuck
against the side of the cups. Continue until all of the disks are floating in the “High Light Intensity” cup.
We can increase the intensity of light that the plant receives by placing plants at a closer distance towards
the light source. The concentration of CO2 in water can be increased by adding NaHCO3, which reacts in
water to form sodium hydroxide and carbon dioxide (Equation 2).
Equation 2
NaHCO3 → NaOH + CO2
2.
3.
4.
5.
1. What part of photosynthesis did CO2 help speed up? The light-dependent or light-independent
reactions? Explain.
Which cup exhibited a faster rate of photosynthesis? High light intensity or low light intensity?
What data support this?
So, what effect did light intensity have on the rate of photosynthesis?
What part of photosynthesis did light intensity help speed up? The light-dependent or light-independent
reactions? Explain.