Student activity AB2.10.1
Book links: Page 32
Lesson reference: B2.10 Rates of photosynthesis Specification links: B2.3.1 a–g
The effect of light on the rate of photosynthesis
Equipment required per group:
Beaker
Metre rule
Lamp
Filter funnel
Boiling tube
Three 7 cm lengths of Canadian pondweed (Elodea)
Sodium hydrogen carbonate
Spatula
Timer or stopwatch
Getting started
You are going to investigate the effect of light intensity on the rate of
photosynthesis using pondweed. This is a good method because any oxygen
given off can be seen as bubbles.
Investigating
1 Place three 7 cm lengths of pondweed in a glass funnel.
2 Put the funnel upside down into a beaker.
3 Place the whole apparatus into a large tank of water that has been left to
stand for several days to remove any chlorine.
4 Put an upside down boiling tube over the end of the funnel.
5 Remove the apparatus from the tank. It should be completely full of water.
6 Add two full spatulas of sodium hydrogen carbonate to the water in the
beaker.
7 Let the apparatus stand for 10–20 minutes to recover from the set up.
8 Place a lamp 100 cm away from the apparatus.
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.
© Oxford University Press 2011
This document may have been altered from the original.
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9 Leave for one minute, then count the number of bubbles released from the
weed in one minute.
10 Move the lamp 10 cm closer to the apparatus and repeat step 9.
11 Record the bubbles released at each 10 cm interval until the lamp is as close
as possible to the beaker of pondweed.
Asking questions
1 Copy and complete the results table below. Your teacher may ask you to pool
class results to produce an average.
Distance
from lamp
(cm)
Number of bubbles produced
Group 1
Group 2
Group 3
Group 4
Average
100
90
80
70
60
50
40
30
20
10
0
2 Draw a line graph of these results. Place the distance on the x-axis and the
number of bubbles on the y-axis.
Spreading the word
A
B
C
D
E
F
G
H
What is the relationship between light and the number of bubbles produced?
Why was sodium hydrogen carbonate added?
What is the limiting factor throughout this experiment?
What other factors would affect the rate?
How could you stop the temperature affecting the rate?
Is counting the bubbles an accurate measure?
How could this be improved?
How could this experiment be adapted to look at the effect of other factors?
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.
© Oxford University Press 2011
This document may have been altered from the original.
89