A rock contains 25% of the potassium-40 it started with. How old is the rock?

answer; ///i believe the correct answer is (aids) acquired immune deficiency syndrome;

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