Variables
- Independent variables : distance of table lamp from the leaves (light intensity)
The light intensity (L) is controlled by placing the source of light which is the lamp, to the ananas comosus leaf disc at different distances,D.
The light intensity is calculated as :
L =1/D²
Several distances were chosen: 10 cm, 15 cm,20 cm, 25 cm, 30 cm, 35 cm
The distance of the lamp to the leaf is measured by using metre ruler.
- Dependent variables : time taken for the leaves to float
The time taken for each ananas comosus leaf disc to float on surface of sodium hydrogen carbonate solution is measured using stopwatch
The rate of the process is calculated using formulae:
Rate =1/Time
- Controlled variables :
- Type and species of leaves
-
The same species of leaf which is Ananas Comosus is used throughout the experiment because the leaf has layer of parenchyma cells which will help them to float when gas bubbles are trapped inside the leaf.
- Size of leaf disks
- Using cork borer, the size of leaf disks is kept constant with the value of 8 mm.
- Power of table lamp
- The power of light bulb is maintained to 100 watt along the experiment.
- Concentration and volume of sodium hydrogen carbonate solution
- To ensure even amount of carbon dioxide is released throughout the experiment
- Time for each experiment to begins
- Stopwatch is only started when the table lamp is switched on.
Materials and Apparatus
Methods
-
10 discs of Ananas Comosus leaves are prepared using cork borer.
- 20 cm3 of sodium hydrogen carbonate solution is measured using measuring cylinder and poured into a beaker.
- All of the disks are inserted into a syringe.
- 2 cm3 or the 20 cm3 sodium hydrogen carbonate inside the beaker is measured and poured into the same syringe.
- The airs inside the syringe is pushed out and then, pull the syringe’s plunger upwards while its nozzle is closed using a thumb.
- All the leaf disks and sodium hydrogen carbonate solution inside the syringe is poured back into the beaker.
- The content of the syringe is then poured into a beaker. The leaf discs are made to a single layer, rather than they are on top of one another.
- The bulb is switched on and stopwatch is started immediately
- The time taken by each leaf disc to float on the surface of sodium hydrogen carbonate solution is measured using stopwatch.
- The experiment is required to be repeated with varying light intensity
- All data are recorded and presented as below.
Data Collection
- Qualitative Data
- Air bubbles are produced from the leaf disks when the syringe’s plunger is pulled outwards.
- All of the leaf disks sink under the water when they are immersed in the sodium hydrogen carbonate solution initially.
- Air bubbles are produced again from the leaf disks after some time they have been immersed in the sodium hydrogen carbonate solution.
- Eventually all of the disks will float on the surface of the sodium hydrogen carbonate solution.
- Quantitative Data
Table 1 : time taken for Ananas Comosus leaf discs to float and the distance of discs from the lamp
Data Processing
The average time taken for ananas comosus leaf disc to float to surface of sodium hydrogen carbonate solution is calculated by using this formulae:
Average =
Table 2 : distance of leaf disks from the lamp and the average time taken for them to float
Light intensity is calculate using the formula
Uncertainties of the light intensity are calculated as follow: -
∆L =2 x light intensity
Table 3 : distance of leaf discs drom the lamp and rate of photosynthesis
Rate of photosynthesis is calculated using the formula
Uncertainties for rates of photosynthesis are calculated as follow: -
∆R = x rate of photosynthesis
Graph 1 : rate of photosynthesis against light intensity
Evaluation
Conclusion
When leaf discs are immersed in a sodium hydrogen carbonate solution (a source of carbon dioxide) and illuminated, the oxygen produced by photosynthesis causes the leaves to float. The time the leaves take to float can thus be used as an indirect measure of the rate of photosynthesis i.e. the more quickly flotation occurs, the faster the rate of photosynthesis.
However this is true only until a certain point is reached. After the point is reached, the rate of photosynthesis will no longer increase but rather decrease. This is because there are other factors such as the denaturation of enzymes or cells.