Question

Randy wants to know whether a soil's porosity affects how easily seedlings grow in it.

Answer 1

Since the main objective of this experiment is to determine the effect of porosity on seedling growth that should be the only independent variable. In short, that is the only variable that should be different to ensure fair testing. 

The answer should be B:

he plants seedlings in soils with different levels of porosity and equal levels of permeability. 

Permeability is not what needs to be tested. If it changes, you may not be able to determine whether it was the porosity or permeability that cause changes.  

Answer 2

Answer: B: different, equal

Explanation:

Since Randy wants to know how porosity affects seedling growth, he needs to design an experiment in which he uses soils of different porosity but keeps everything else the same. This means that his experiment should involve soils with equal levels of permeability, since this factor can also affect seedling growth.  Randy is likely to find that most seedlings succeed in porous soils, because the open spaces between particles give them room to grow.