Biology Example Question #4 describe the lock and key model of enzyme activity and how induced fit model extends it

Enzymes are proteins, which have the specific role of lowering the activation energy of reactions. A key fact about them, is that they are not used up during a reaction, and can thus be reused for multiple reactions. Enzymes have a Quaternary structure, making them globular in shape. Each of them has a so called active site, whereupon a substrate binds to it. The way the enzymes then lower the activation energy of a reaction is by stressing the bonds of the reactants (substrate), thus speeding up the process, and increasing rate of reaction. Though, it is important to note, that an enzyme will not increase the amount of product formed, merely the rate at which it is formed. 

"labeled for reuse" https://pixabay.com/p-390792/?no_redirect

The lock and key model goes by the premise that there is a specific enzyme for each substrate. Which would mean there is an absurd amount of enzymes. Each of the active sites are perfectly shaped to fit the substrate, and thus there is only one enzyme that fits each substrate. It can thus perfectly stress the bonds of its particular substrate. However, the fact that so many enzymes would have to exist led to a revision of this particular model to the induced fit model.
This model takes more of a "glove and hand" approach, whereby the enzyme is roughly shaped like the substrate, and once one enters its active site it will shape itself around it. Making slight modifications in form until its active site fits the substrate. Once this has occurred it can once again stress the bonds of the substrate speeding up the reaction. With this model one enzyme can "fit" multiple substrates, thus reducing the number of enzymes needed. 

Thank you again to my biology teacher for teaching me everything I know about this!