6

Question 1

Manipulative experiments

Answer 1

all of the above:

Allow scientists to directly assess how changes in one component of a system influence the other components; allow scientists to examine not only correlations among data, but also causality; ideally after only one variable at a time

Question 2

Each time a species goes extinct

Answer 2

all of the above:

there are evolutionary consequences; part of the evolutionary history of life on earth is lost; a twig on the tree of life is lost forever