so rate ∝ 1
d2
as LI ∝ 1
d2
Prediction
I think that the closer the lamp is to the test tube, the faster the rate of photosynthesis will be.
Results – anomalies in red
Calculations
5cm:
LI = 1 x 100 000
d2
LI = 1 x 100 000
52
LI = 1 x 100 000
25
LI = 4000
10cm:
LI = 1 x 100 000
d2
LI = 1 x 100 000
102
LI = 1 x 100 000
100
LI = 1000
15cm:
LI = 1 x 100 000
d2
LI = 1 x 100 000
152
LI = 1 x 100 000
225
LI = 444
30cm:
LI = 1 x 100 000
d2
LI = 1 x 100 000
302
LI = 1 x 100 000
900
LI = 111
50cm:
LI = 1 x 100 000
d2
LI = 1 x 100 000
502
LI = 1 x 100 000
2500
LI = 40
Analysis
Graph 1 shows how the bubble length changes as the distance the lamp is away changes. The relationship is that as the distance of the light increases, which means that there is less light, the average bubble length decreases. This means that the amount of oxygen decreases, therefore the rate of photosynthesis decreases. This also means that distance is inversely proportional to the rate of photosynthesis.
Graph 2 is related to graph 1 because instead of the distance of the light, light intensity is shown. The intensity of the light and the distance of the light are related because as the distance of the light from the plant decreases, the light intensity increases.
Graph 2 goes through the origin which means that when there is no light, no photosynthesis happens. But as the light intensity increases, the average bubble length also increases proportionally. The straight line clearly shows this.
However, in reality, the line levels off. This is because a further increase in light intensity doesn’t result in a larger bubble length. This is because light intensity no longer becomes a limiting factor and the plant cannot produce more oxygen, instead other limiting factors come into play, such as temperature.
The reason that the rate of photosynthesis increases with light intensity can be explained using the equation of photosynthesis:
Carbon dioxide + water → glucose + oxygen
6CO2 + 6H2O → C6H12O6 + 6O2
For the reaction to happen, light energy is needed. This light is absorbed by the green pigment chlorophyll in the chloroplasts of the palisade cells. This chlorophyll traps energy from sunlight. This means that the more the light (and therefore the light intensity), the more energy the plant has. This energy is used by the enzymes catalysing the photosynthesis reaction. So the more energy the catalysts have, the more they can catalyse the reaction. This means that more oxygen is produced (shown by the length of the bubble).
Evaluation
Having carried out my experiment, I am going to evaluate my method and practical skills.
While setting up the experiment, I found it hard to set up the plastic tube which connects the scale and the syringe. However, after I solved the problem, the rest of the experiment went smoothly.
I found two anomalous results on my results table. I decided that 29mm and 12mm were wrong because they were far off the other results. 29mm was 20mm off the next smallest result and 12mm was 9mm off the next smallest result. They could have been caused by me reading off the measurement wrongly on the scale.
Moreover, the measurements may not have been accurate enough. Reading off a scale could cause me measuring it wrongly because I could not see the exact number with my eyes. The experiment could have been made fairer if I’d have used a piece of electronic equipment to measure the size of the bubbles.
Another problem with the experiment could have been that the experiment was not reliable enough. There were many points of error in the experiment. For example, the lamp was not 100% efficient. It converted some of the energy to heat energy and this could have caused an increase in temperature inside the test tube. Heat gives more energy to the enzymes and this could have caused an increase in the rate of photosynthesis.
Another problem was that I could not increase the light intensity with the same lamp. This was because the lamp was too near at 4000 lux for me to increase the intensity. This could have caused less accurate results.
This could give an idea of another experiment I could do. I could do the exact same experiment, but instead use a brighter bulb.
