🔬 Investigation Overview

Question: How does light intensity affect the rate of photosynthesis?

Equipment: Elodea (pondweed) plant, light source (lamp), ruler, beaker of water, stopwatch, oxygen bubble counter.

Method Summary: The Elodea plant was placed in a beaker of water. A lamp was positioned at distances of 10 cm, 20 cm, 30 cm, 40 cm, and 50 cm from the plant. The number of oxygen bubbles produced in 1 minute was recorded for 5 trials at each distance.

Raw Data Table

Use the data below to answer the questions in the following sections.

Light Distance (cm) | Trial 1 | Trial 2 | Trial 3 | Trial 4 | Trial 5
10 cm                   | 30      | 28      | 32      | 31      | 29
20 cm                   | 20      | 22      | 19      | 21      | 20
30 cm                   | 12      | 15      | 13      | 14      | 12
40 cm                   | 8       | 9       | 7       | 8       | 7
50 cm                   | 3       | 4       | 5       | 3       | 4

📊 Part 1: Data Analysis

1. Calculate the average number of bubbles produced per minute at each distance. Show your working.

2. Complete the results summary table below using your calculated averages:

Light Distance (cm)    | Average Bubbles per Minute
10 cm                          | _________
20 cm                          | _________
30 cm                          | _________
40 cm                          | _________
50 cm                          | _________

3. In the box below, draw a line graph of your results. Label your axes clearly — include units!

4. Identify the independent variable and the dependent variable in this investigation.

Independent variable: _________________________________________

Dependent variable: _________________________________________

5. Which distance produced the highest rate of photosynthesis? Why do you think this is?

✏️ Part 2: Understanding and Evaluation

6. What gas are the bubbles made of, and which part of the photosynthesis equation does this relate to?

Carbon dioxide — a reactant in photosynthesis

Oxygen — a product of photosynthesis

Oxygen — a reactant in photosynthesis

Carbon dioxide — a product of photosynthesis

7. Write the word equation for photosynthesis.

_________________________________________ → _________________________________________ + _________________________________________

8. Describe the trend shown in your graph. Use data from your results to support your answer.

9. Select all factors that could affect the rate of photosynthesis (besides light intensity):

Temperature of the water

Colour of the beaker

Carbon dioxide concentration

Amount of chlorophyll in the plant

The brand of the stopwatch

10. Suggest one improvement to this investigation and explain how it would make the results more reliable.

11. Does your data support the hypothesis that "increasing light intensity increases the rate of photosynthesis"? Explain your answer using evidence.