When eating plants or plant parts, humans generally eat fruits. Unlike cows
we don't eat grass. Why not? Does it
relate to the cellular structure of plants i
any way? If so, how?

we dont eat it bc it tast bad

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.

that is true   : ) hope this you