A student investigates the effect of organic fertilizer on the number of earthworms living in pasture soil.
The student collects 10 cm310\text{ cm}^310 cm3 soil samples from a pasture field where organic fertilizer is not used. She also collects 10 cm310\text{ cm}^310 cm3 soil samples from a pasture field where organic fertilizer is used.
The table shows the student's results.
| Treatment | Average number of earthworms per 10 cm310\text{ cm}^310 cm3 of soil |
|---|---|
| organic fertilizer not used | 32 |
| organic fertilizer used | 54 |
Calculate the percentage change in the average number of earthworms when organic fertilizer is used. Show your working.
Name the dependent variable in the student's investigation.
Describe a method the student could use to obtain a valid comparison of the number of earthworms in each pasture field.
Growers want to use selective breeding to increase the sugar content in sugar beet plants. Explain how the process of selective breeding can be used to produce sugar beets with a higher sugar content.
9 exam-style questions on Edexcel IGCSE Biology Selective breeding. Each one has a worked solution and a mark scheme showing where the marks go.