Coral reefs which surround an island are called a0 and the restricted waters behind the barrier form the marine environment of a(n) a1.

the most common type of reef is the fringing reef. this type of reef grows seaward directly from the shore. they form borders along the shoreline and surrounding islands.

an active site is a region that is present on an enzyme where the reactants or the substrate molecules we can say bind and experience a chemical reaction. the substrate is basically a reactant whose concentration is changing and that is converting into a product after binding at the active site of an enzyme

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link: