Have developed circulatory systems to transport materials. unicellular multicellular both a and b none of above

answer; /// i believe that the correct answer is; ///a combination of the birth and death

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