Why would rabbits on different parts of an island have different size ears ?

Evolution

Explanation:

Because the rabbits of different parts of the island can't mate easily, differences in appearance show up as time passes. In the rabbits' case, one of the most notable differences is the size of the ears.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products