Even land that is now very diverse once started out as what?

As of right now, the land is pretty spread out. But millions of years ago, like, we're talking dino time, all the land was just one chunk. This chunk was called Pangaea, or Pangea. But before everything split apart into multiple continents, there was just one; a supercontinent. Hope that helps!

answer; the tunica intima also called tunica interna, consists of elastic fibers,connective tissue and smooth muscle cells;

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