🔬 Part 1: Investigation Setup

Investigation Question

How does light intensity (measured by distance from light source) affect the rate of photosynthesis in aquatic plants (measured by oxygen bubbles produced per minute)?

Equipment

Tick each item as you set up your experiment:

Aquatic plant (e.g., Elodea)

Beaker of water

Lamp / light source

Ruler (measuring in centimetres)

Stopwatch

Sodium bicarbonate solution

Pencil and recording sheet

Method

Follow these steps carefully during your investigation:

1. Set up the beaker of sodium bicarbonate solution and place the Elodea plant inside, cut end facing upward.

2. Position the lamp 10 cm from the beaker using a ruler to measure the distance accurately.

3. Allow the plant to adjust for 1 minute before recording.

4. Count the number of oxygen bubbles produced in 1 minute and record in the table below.

5. Repeat step 4 two more times at 10 cm to get 3 trials.

6. Move the lamp to 20 cm and repeat steps 3–5.

7. Continue for distances of 30 cm, 40 cm, and 50 cm.

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

📊 Part 2: Results Table

Record your results below. Then calculate the average number of bubbles for each distance.

Average = (Trial 1 + Trial 2 + Trial 3) ÷ 3

Raw Data Table — Oxygen Bubbles Produced per Minute

| Distance from Light | Trial 1 | Trial 2 | Trial 3 | Average |
|---------------------|---------|---------|---------|---------|
| 10 cm | | | | |
| 20 cm | | | | |
| 30 cm | | | | |
| 40 cm | | | | |
| 50 cm | | | | |

Note: Show your average calculations in the space below.

Calculate your averages here (show working):

✏️ Part 3: Investigation Report Questions

1. Identify the independent variable (what you changed) in this investigation.

2. Identify the dependent variable (what you measured) in this investigation.

3. List two controlled variables (things kept the same) and explain why they must stay the same.

4. Was your investigation a fair test? Circle your answer and explain why.

Yes — it was a fair test

No — it was not a fair test

5. Write a conclusion for your investigation. Use your data to support your answer and refer to the relationship between light intensity and the rate of photosynthesis.

6. Suggest two improvements you could make to this investigation to increase the reliability of your results.

Improvement 1: _____________________________________________________________________________

Improvement 2: _____________________________________________________________________________

7. Why did we use sodium bicarbonate solution instead of plain water in this experiment?