In a way, biology is only an applied science, applying physics as a tool for the analysis of living systems. However, there are distinctions between physical and biological events. Suppose a process, left to itself, is likely to occur 999 times in one way for each time that it occurs in another. The physicist concerns himself primarily with the first way. Physics is the science of the probable.
Biology is the science of the improbable.
On principle, biological reactions must be improbable. If man's cells worked only through the probable reactions, they would soon run down in order to regulate itself, a cell must use improbable reactions and must make them take place through very specific tricks. The cell may make use of just that one way in a thousand that the physicist ignores. The cell finds a way to make the reaction go at just the right moment and at the desired rate. The reaction may be improbable, but if it is thermodynamically possible, the cell will find a way to use it.