🔍 Investigation Question

Does the distance of a light source from an aquatic plant affect the rate of photosynthesis, as measured by the number of oxygen bubbles produced per minute?

🧪 Equipment

• Aquatic plant (e.g. Elodea / pond weed)
• Lamp with a clear bulb (60 W)
• Beaker (500 mL)
• Water (at room temperature, approximately 20°C)
• Ruler (30 cm)
• Stopwatch or timer
• Sodium hydrogen carbonate solution (to supply CO₂)
• Clamp stand and boss clamp
• Pencil and data table

📋 Method

Step 1: Set up the beaker and fill it with sodium hydrogen carbonate solution.

Step 2: Cut a fresh 10 cm sprig of Elodea and place it in the beaker with the cut end facing upward.

Step 3: Position the lamp 10 cm from the beaker. Allow the plant to adjust for 2 minutes before starting.

Step 4: Start the stopwatch and count the number of oxygen bubbles produced from the cut end of the plant in 1 minute. Record the result in the data table.

Step 5: Repeat Step 4 two more times at the same distance to get three trials. Record all results.

Step 6: Move the lamp to 20 cm from the beaker. Repeat Steps 4 and 5.

Step 7: Repeat for distances of 30 cm, 40 cm, and 50 cm, recording three trials at each distance.

Step 8: Calculate the average number of bubbles for each distance.

Keep all other variables the same throughout the experiment (same plant, same water temperature, same room lighting).

📊 Raw Data Table

Table 1: Number of oxygen bubbles produced by Elodea in 1 minute at different distances from a light source.

Distance from Light Source (cm)	Trial 1 (bubbles/min)	Trial 2 (bubbles/min)	Trial 3 (bubbles/min)	Average (bubbles/min)
10	48	51	46
20	34	36	33
30	22	20	24
40	13	11	14
50	6	7	5

Use this data to write your own fair test investigation report. Remember to calculate the averages in the final column.