A. Why does Bromothymol solution change colour of the beans ?

Bromothymol blue solution is an indicator that changes color in the presence of a weak acid or base. So release of carbon dioxide into water which turns into a weak acid. Therefore the cellular respiration is the driving the color change. ... both the release of gas and cellular respiration.

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.