Some students investigate the decomposition of dead plant waste. They make a composter from plastic bottles with liquid drain holes at the bottom and varying numbers of air holes near the top.
Why do the students make air holes in the composter? Select one option:
The students want to see if the number of air holes affects the rate of decomposition.
The table shows their results:
| Number of air holes | Mass at the start (g) | Mass after 6 weeks (g) |
|---|---|---|
| 2 | 400 | 365 |
| 4 | 400 | 340 |
| 8 | 400 | 322 |
| 12 | 400 | 315 |
(i) Calculate the loss in mass per week of the composter and plant waste with 12 air holes. Give your answer to 3 significant figures.
Describe the effect of the number of air holes on the rate of decomposition of the plant waste.
The students made sure that all composters and plant waste had a mass of 400 g400\text{ g}400 g at the start of the experiment. Explain why this helps the students to analyse the results.
What is the independent variable in the students' investigation?
During the experiment, water drips through the drain hole at the bottom of the composter onto the bench. Explain why this can produce inaccurate results and how they can change their method to correct this.
44 exam-style questions on OCR GCSE Biology Practical skills. Each one has a worked solution and a mark scheme showing where the marks go.