Student worksheet
Activity 8: The effect of CO2 on the rate of photosynthesis
Objective
• To determine the limiting effect of different
concentrations of carbon dioxide on the rate of
photosynthesis
Equipment/materials
• One young cabbage leaf or similar, such as spinach
or Hedera
• Cork borer or straw
•
5 cm3 syringe
•
•
Four 5 cm3 different concentrations of sodium
hydrogen carbonate solution (0.0 M, 0.2 M, 0.4 M and
0.6 M)
Plasticine®
•
•
Bench lamp with 40 W bulb
Stopwatch
Safety
Procedure
1. Cut out 20 leaf discs from the cabbage leaves using a
cork borer or straw.
2. Remove the plunger from the syringe and place a
finger over the nozzle to prevent liquid running out, and
then fill with 5 cm3 of 0.2 M sodium hydrogen carbonate
solution.
3. Carefully add five of the leaf discs to the solution in the
syringe, taking care not to damage them.
4. Gently replace the syringe plunger and point the
syringe upwards.
5. Push out all the air by slowly pushing the plunger as far
as it will go.
6. Place your finger over the syringe nozzle and gradually
pull the plunger down. Bubbles will appear on the
surface of the leaf discs as the air is drawn out of them.
7. Tap the syringe barrel so that the bubbles rise to the
top and the discs start to sink to the bottom.
8. Repeat this process until all the discs are at the bottom
of the syringe.
9. Use a lump of Plasticine® to hold the syringe barrel
vertically under a bench lamp, with the nozzle pointing
up, and start the stopwatch.
10. Time how long it takes for each disc to rise to the
surface.
11. Repeat steps 2–10 for each concentration of sodium
hydrogen carbonate.
12. Record your times in a suitable table.
Data/diagram
Figure 8
Analysis of results
From the examiner
• A limiting factor is one that limits the rate of
photosynthesis.
• Where there are several limiting factors, the one that
is at its lowest will limit the rate of photosynthesis.
Questions
1. Why did the discs rise to the surface of the syringe?
2. Explain the difference in rate of photosynthesis between the different sodium hydrogen carbonate solutions.
3. What other limiting factors may affect photosynthesis and so affect your results?
4. How did you try to minimise the effect of other limiting factors?
5. How could this information be used by a horticulturist when growing a crop in a greenhouse?
Practical activities have been checked for health and safety advice by CLEAPSS. All users will need to review the
risk assessment information and may need to adapt it to local circumstances.
© Pearson Education Ltd 2009
This document may have been altered from the original
8/30
Teacher worksheet
Activity 8: The effect of CO2 on the rate of photosynthesis
Objective
• To determine the limiting effect of different
concentrations of carbon dioxide on the rate of
photosynthesis
From the examiner
• Discuss limiting factors as those factors that limit the
rate of photosynthesis when they are present at low
amounts.
• Where there are several limiting factors, the one that
is at its lowest will limit the rate of photosynthesis.
Safety
Notes on procedure
• The cork borer or straw should easily cut neat discs in
the leaf.
• It is easy to damage the leaf discs when adding them
to the solution in the syringe – this will affect their gas
production so students must remove them from the
straw or cork borer carefully.
• When students are using the syringe to push out all the
air it is important that they do this slowly.
• Pulling the plunger out again will draw air from the air
spaces within the leaf discs. This will need to be
carried out several times to ensure all the air is drawn
out – if not, the discs will not sink to the bottom.
• Tapping the syringe barrel allows the bubbles to detach
from the surface of the discs and rise to the top – this
will then allow the discs to sink.
• Discs will usually start to rise after a few minutes.
Answers
1. As the leaf cells photosynthesise, they produce
oxygen gas which fills the air spaces and the discs
rise.
2. At low sodium hydrogencarbonate concentrations,
the leaf discs will not be supplied with sufficient
carbon dioxide, so it will be a limiting factor and less
gas will be produced. At higher concentrations,
carbon dioxide will not be a limiting factor so more
gas will be produced.
3. Temperature and light are both limiting factors in
photosynthesis and will affect the volume of gas
produced and thus the time taken for the discs to
rise.
4. Students should describe the measures they took
during the experiment or describe some measures
they would take to improve the task.
5. Temperature regulation and carbon dioxide
concentration can be increased using a greenhouse
heater. Regulation of light would also improve crop
yield.
Practical activities have been checked for health and safety advice by CLEAPSS. All users will need to review the
risk assessment information and may need to adapt it to local circumstances.
© Pearson Education Ltd 2009
This document may have been altered from the original
8/30
Technician worksheet
Activity 8: The effect of CO2 on the rate of photosynthesis
Objective
• To determine the limiting effect of different
concentrations of carbon dioxide on the rate of
photosynthesis
Safety
Requirements per student*/group of students
Notes
One young cabbage leaf or similar, such as young spinach
or Hedera
Young radish leaves are also suitable for this experiment, if
available.
Cork borer or plastic straw
5 cm3 syringe
Four 5 cm3 different concentrations of sodium hydrogen
carbonate solution (0.0 M, 0.2 M, 0.4 M and 0.6 M)
Plasticine®
Bench lamp with 40 W bulb
Stopwatch
Notes
Hedera will not cut easily with a straw as the leaves are too tough and so a cork borer must be used.
Practical activities have been checked for health and safety advice by CLEAPSS. All users will need to review the
risk assessment information and may need to adapt it to local circumstances.
© Pearson Education Ltd 2009
This document may have been altered from the original
8/30