What are body systems composed of

Organ systems

Explanation:

Because cells make up tissues and tissues make of organ systems and organ systems make up body systems. Different organs are found in different body systems.

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

the answer is 100% density i've answered this question before and done the quiz myself.