For two populations to evolve into two species that look different, what must happen
a. extinction
b. competition
c. continental drift
d. reproductive isolation

Crossing over is a method of (blank)?

Compare the parts of a cell and the cell as a whole to another common nonliving system (i.e., a car, a city, describe the parts of a cell and their primary function.

Which nutrient tends to cycle within a single ecosystem?