Sort the examples into proper mechanisms of reproductive isolation. prezygotic postzygotic the inability of red and purple sea urchins to mate due to gametic incompatibility a sterile zonkey formed from the mating of a donkey and a zebra different mating calls for two different grasshopper species the death of a zygote after few weeks of formation

The mechanisms of reproductive isolation prevent the reproduction of two individuals from different species. The prezygotic mechanisms disrupt the stages of reproduction before the forming of the zygote or prevent the mating at the start, and the postzygotic mechanisms affect the stages of reproduction after the forming of the zygote.
So, the first and the third example (the urchins and the grasshoppers) show the prezygotic mechanism, as the two individuals are not able to mate or form a zygote.
The second and the fourth example ( zonkey and the death of a zygote) show the working of the postzygotic mechanisms, as the zygote is formed, but it seems to be inviable, and the zonkeys are sterile, preventing the individual to reproduce.

Cells of an organism tell each other when predators are near.