How does stomach acid help digestion?

Stomach acid is actually hydrochloric acid. Stomach acid is very strong. It can even erode metal if you give it time. Stomach acid breaks down different aspects of food, especially proteins, The body needs broken down particles from food so that it could use it. But, the stomach is not the only thing that breaks down food - the small intestines does too, with bile!

So stomach acid makes food particles smaller so that the body can process it further.

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.

producers: apple trees, potatoes, carrots, grains, acorns, cabbage, grass, corn, lettuce

consumers: deer, mice, rabbits, chickens, squirrels, horses, worms, cows

predators: eagles, frogs, wolves, owls