1. why is energy needed for active transport?

Active transport is requires energy because it is not a passive process.

Explanation:

The molecule has to go against the concentration gradient.

Why is energy needed for active transport? Because active transport is required to have energy, but it is not a supine process. The molecule basically has to go AGAINST the concentration slope. For this reason, it requires energy to be carried by the carrier proteins.

Hope this helps yaa!! :-)

b.have there own function.

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.