Method
1) add 200 cm of “pond” water and one spatula full of sodium hydrogen carbonate into a beaker
2) cut a sprig of pondweed 5 cm long
3) place a funnel, a boiling tube half-filled with water and the pondweed into the beaker of water as shown in the diagram
4) place the thermometer in the water of beaker and record the temperature
5) wait for the plant to begin to produce a steady stream of bubbles
6) shield the set-up from unwanted light, e.g room lighting, sunlight, etc.
7) set up the lamp at 30 cm away from the beaker of water
8) wait 2-3 minutes for the plant to adjust to the new conditions
9) using a stopwatch, count the number of bubbles produced in a minute and record it down
10) measure and record the temperature of the water in the beaker regularly to ensure a fair test
11) repeat these measurements 3 times and calculate the average number of bubbles produced in a minute
12) repeat step (1-11) for a range of closer distances
Prediction
I predict that as the light intensity increases, the rate of photosynthesis (number of bubbles produced a minute) will increase steadily but only up to a certain point. This is because as the reaction occurs, heat is produced, causing the temperature to increase. If the temperature gets too high, it will denature the chlorophyll enzymes and the pond weed will stop photosynthesizing and producing bubbles.
Table
Description and Explanation
The closer the lamp is to the pondweed, the higher the rate of bubbles produced. But as I moved the lamp 5 cm away from the plant each time, the rate of bubbles produced starts to decline significantly. The reason is because plants uses light to carry out photosynthesis which produces bubbles of gas-oxygen in the process. If the light intensity declines, the rate of photosynthesis at which the plants conducts will decline as well.