An agricultural student investigates the effect of a seaweed-derived biostimulant on the number of Rhizobium root nodules in soybean plants.
The student collects root zone samples from a soybean field where the biostimulant is not used, and from a field where the biostimulant is used, and counts the nodules on each plant root system.
The table shows the student's results.
| Treatment | Average number of nodules per soybean plant root system |
|---|---|
| Biostimulant not used | 15 |
| Biostimulant used | 24 |
Calculate the percentage change in the average number of root nodules when the biostimulant 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 nodules in each soybean field.
Growers want to use selective breeding to increase the oil content in soybean seeds. Explain how the process of selective breeding can be used to produce soybeans with a higher oil yield.
