🔬 Part 1: Investigation Setup

Research Question

How 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?

Hypothesis

1. Write your hypothesis using an IF/THEN/BECAUSE format:

Variables

2. Identify the variables for this investigation:

Independent variable (what you change): _______________________________________________

Dependent variable (what you measure): _______________________________________________

Controlled variables (keep the same — list at least THREE):

a) _______________________________ b) _______________________________ c) _______________________________

Materials

Tick the equipment you will use in this experiment:

Aquatic plant (e.g. Elodea)

Beaker of water (500 mL)

Lamp / light source

Ruler or metre ruler

Stopwatch or timer

Sodium hydrogen carbonate solution

Thermometer

Pencil and results table

Method

3. Number these steps in the correct order (1–7):

_____ Count and record the number of oxygen bubbles produced in one minute.

_____ Set up the lamp 10 cm from the beaker containing the Elodea plant.

_____ Repeat the experiment at distances of 20 cm, 30 cm, 40 cm, and 50 cm.

_____ Allow the plant to adjust to the light for 30 seconds before counting.

_____ Add sodium hydrogen carbonate solution to the water to ensure carbon dioxide is available.

_____ Repeat each distance trial 3 times and calculate the average bubble count.

_____ Record all results in your data table and check controlled variables remain constant.

Fair Test Check

4. Why is it important to repeat each trial 3 times?

📊 Part 2: Results

Raw Data Table

Record the number of oxygen bubbles per minute at each distance. Complete all trials.

| 10 cm | _______ | _______ | _______ | _____________________ |

| 20 cm | _______ | _______ | _______ | _____________________ |

| 30 cm | _______ | _______ | _______ | _____________________ |

| 40 cm | _______ | _______ | _______ | _____________________ |

| 50 cm | _______ | _______ | _______ | _____________________ |

Graph

5. Plot your average results on the axes below. Label both axes, add a title, and draw a line of best fit.

✏️ Part 3: Investigation Report

6. Analysis — Describe the trend shown in your graph. What happens to the rate of photosynthesis as the light source moves further away?

7. Scientific Explanation — Using your knowledge of photosynthesis, explain WHY this trend occurs. Include the word equation for photosynthesis in your answer.

8. Evaluation — Identify ONE source of error in this experiment and explain how it could affect your results. Suggest how you could improve the method.

9. Conclusion — Was your hypothesis supported? Write a conclusion that refers to your data and explains what you found.

10. Extension — A scientist claims that temperature has a greater effect on photosynthesis than light intensity. Describe how you could design a follow-up experiment to test this claim. What would you change, measure, and keep the same?