I think he's being a little facetious - what he probably means is that if you attempt to get any true scientific rigor of that is going on in biological or chemical systems you end up facing the limits of physics in being able to explain what is going on. So rather and try to have scientific rigor, you just accept things the way they are and memorize the outputs and if anyone asks "why is it like that", your answers are either:

* Because God said so

* Find out yourself and get a nobel prize

Either way, even if you don't know what the answers are, you can still do serious work at a higher level of abstraction.