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Photosynthesis Rate Investigation Worksheet

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Photosynthesis Rate Investigation Worksheet

Hana is investigating whether the distance of a lamp changes the rate of photosynthesis in pond weed. Use the information and results on this sheet to plan, analyse and evaluate the investigation. If you carry out the experiment, follow your teacher’s instructions and keep water away from electrical equipment.

Plan a fair test

In this investigation, the lamp is moved to different distances from a piece of pond weed. The oxygen bubbles released in one minute are counted as an estimate of photosynthesis rate.

1.Which gas do the bubbles represent, and what does counting them help Hana estimate?

2.Write a prediction for what may happen to the number of oxygen bubbles per minute as the lamp is moved farther away. Give a science-based reason.

3.Identify the independent variable Hana changes and the dependent variable she measures.

4.Choose two conditions Hana should keep the same to make this a fair test.

The length of pond weed and the time spent counting bubbles
The lamp distance and the number of bubbles
The bubble count and the colour of the results table
The distance and the number of trials

Results from Hana’s trial

Hana counted bubbles for one minute at each distance. She repeated each measurement three times.

Lamp distance

Trial 1

Trial 2

Trial 3

10 cm

20 cm

30 cm

5.Calculate the mean bubble count per minute at each distance. Show your three answers.

6.At which lamp distance was the mean photosynthesis rate highest? Support your answer with the mean bubble count.

7.Describe the pattern in the mean bubble counts as the lamp distance increases from 10 cm to 30 cm.

Explain and improve

Use evidence from the results and your understanding of photosynthesis to explain what happened.

8.Explain why moving the lamp farther away may have lowered the bubble count. Include the idea of light intensity.

9.The 20 cm trial counts were 15, 17 and 16 bubbles. Why is repeating the measurement useful, and are these results consistent?

10.Hana wants to test whether water temperature affects the bubble count. Name one change she should make and two conditions she should keep the same.