What types of organisms carry out cellular respiration

well, that's easy; the answer's c, "it reduces contamination of the water and substrate of the estuary."

substitution is the answer in this case

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