Where is oxygen added to the blood?

Explanation:

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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

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex