A student investigates the effect of a mycorrhizal fungi inoculant on the average number of feeder roots in agricultural soil.
The student collects 15 cm3 soil samples from a plot where the mycorrhizal inoculant is not used. She also collects 15 cm3 soil samples from a plot where the mycorrhizal inoculant is used.
The table shows the student's results.
| Treatment | Average number of feeder roots per 15 cm3 of soil |
|---|---|
| Mycorrhizal inoculant not used | 24 |
| Mycorrhizal inoculant used | 57 |
Calculate the percentage change in the average number of feeder roots when the mycorrhizal inoculant 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 feeder roots in each plot.
Farmers want to use selective breeding to increase the protein content of quinoa grains. Explain how the process of selective breeding can be used to produce quinoa plants with a higher protein content.
