Since in the lock and key model, the lock is only suitable for one key to unlock, only one pattern of key is able to do that, so, to compare it with enzymes, it means that the active site of enzyme is only suitable to bind one type of substrate to it, not other substrates.
We call this property of enzyme the specificity of enzyme. If the active site of an enzyme is changed or loss its three dimensional patterns, it can no longer function as a biological catalysts to speed up chemical reactions.
If I am not wrong, I believe the answer is Producers. The reason as to why I say that producers is the answer is because in every food chain, there needs to be a base. That base is what provides the starting energy that will later on move up in the food chain.
Aerobic bacteria can be used to use the available oxygen in the water to degrade the pollutants in the waste and convert it into energy it can use for its metabolic processes.
