Page 28 - Ranger SPM 2022 Biology

Biology SPM Chapter 2 Leaf Structure and Function

2. Rate of photosynthesis is calculated based on the following formula:
Number of gas bubbles released
Rate of photosynthesis =
Time
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Result:
Distance of Number of gas bubbles released Photosynthesis
Light
Hydrilla sp. intensity in 2 minutes rate (number of
from light –1 gas bubbles /
source (cm) (cm ) 1 2 3 Average minute)
10 0.100 29 30 31 30 15
20 0.050 27 29 28 28 14

30 0.033 24 22 23 24 12
40 0.025 16 15 14 16 8
50 0.020 3 5 4 4 2
Form 5

Photosynthesis rate (Number of air bubbles/minute) 20 5
15
10

0
0.02 0.025 0.033 0.05 0.1
Light intensity (cm )
–1
Discussions:
1. As the light source is further away from the Hydrilla sp., the light intensity
decreases whereas as the light source is nearer to the Hydrilla sp., the light
intensity increases.
2. As the light source is further away from the Hydrilla sp., the lower light intensity
causes less gas bubbles to be released, hence the decrease in photosynthesis
rate.
3. As the light source is nearer to the Hydrilla sp., the higher light intensity causes
more gas bubbles to be released, hence the increase in photosynthesis rate.
4. This is because as the light intensity increases, more light energy is absorbed by
the chlorophyll to breakdown water molecules during photolysis of water and to
generate more ATP from ADP to synthesise carbohydrate in light-independent
reactions.
Conclusion:
As light intensity increases, photosynthesis rate of Hydrilla sp. also increases.
The hypothesis was accepted.

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F5 Chapter 2.indd 223 3/29/22 4:35 PM