Independent variable:
Distance from the lamp (light intensity)
Dependent variable:
pH of the solution (rate of photosynthesis)
Controlled variables:
- Equal (75 ml) amount of water to be put in each beaker was ensure by the measuring marks on the beaker itself. This helps to have the same ratio between NaCOH3 and water in all 5 beakers
- Exactly 1g of NaHCO3 was weighted using balance then put into each beaker. This keeps the concentration of NaHCO3 (which supplies CO2) constant; therefore increase accuracy of the result. If NaHCO3 was put in different amount into each beaker, the measure of pH change will be different.
- The solution in each beaker was tested for pH before the experiment to ensure they have the same pH to start with (same amount of NaHCO3)
- Distilled water was used because it contains no unknown substances that might affect the experiment
- All same size beakers so all plants can have the same environment
-
The plants were taken from the same mother plan. So all have the same characteristics
- All plants have same length ensured by Cm ruler
- Distance from is lamp was kept accurate by the 1 metre ruler
- The time was kept accurate by stop watch
- Different plants are used every new experiment so all of them have the same start for photosynthesis
Results:
Table 0
Table 0 shows the pH level of each 5 beakers before the experiment
Table 1
Table 1 shows the pH taken from beaker A, which was at 20 Cm distance from the lamp at the time interval 2, 4, 6 and 8 minutes.
Graph 1
Graph 1 shows the result from table 1 on graph
Table 2
Table2 shows the pH taken from beaker B, which was at 40 Cm distance from the lamp at the time interval 2, 4, 6 and 8 minutes.
Graph 2
Graph 2 shows the result from table 2 on graph
Table 3
Table 3 shows the pH taken from beaker C, which was at 60 Cm distance from the lamp at the time interval 2, 4, 6 and 8 minutes.
Graph 3
Graph 3 shows the result from table 3 on graph
Table 4
Table 4 shows the pH taken from beaker D, which was at 80 Cm distance from the lamp at the time interval 2, 4, 6 and 8 minutes.
Graph 4
Graph 4 shows the result from table 4 on graph
Table 5
Table 5 shows the pH of the controlled beaker E which has no presence of lamp at the time interval 2, 4, 6 and 8 minutes
Graph 5
Graph 5 shows the result from table 5 on graph
Conclusion:
All 4 results from graph 1, 2, 3 and 4 (distance from the lamp 20, 40, 60, 80 Cm) show an increase in pH of the solution (from pH 9 at the start) over 8 minutes as light intensity increases. This means light intensity does affect the rate of photosynthesis.
The controlled shows no increase in pH. This suggests that there is no other extraneous variable that affect the rate of photosynthesis except light.
The graphs shows that it takes longer for the beakers from further off the lamp beakers to have a pH change. For instance graph 3 shows beaker at 60 Cm from the lamp (low light intensity) have only increase 1 pH (from 10 to 11) in 6 minutes (from 2 minutes till 8 minutes). Graph 1 at the same time interval has increase 2 pH (from 11 to 13). This result supports the hypothesis as light intensity increases, rate of photosynthesis also increases.
Evaluation:
The experiment was success. There is no anomaly in the result. Extraneous variables was minimised by strict controls and careful planning. However the result would be more accurate if instead of using pH universal indicator, a digital pH measuring indicator should be used because it was very hard to identify the colour as well as the pH from the universal indicator. This caused a lot of disagreement during the experiment between my partner and wasted time.
