Our goal is to present the key observations and unifying concepts upon which modern biology is based; it is not a survey of all biology! Once understood, these foundational observations and concepts should enable you to approach any biological process, from disease to kindness, from a scientific perspective. To understand biological systems we need to consider them from two complementary perspectives; how they came to be (the historic, that is, evolutionary) and how their structures, traits, and behaviors are produced (the mechanistic, that is, the physicochemical)

See how the equation form of Ohm's law relates to a simple circuit. Adjust the voltage and resistance, and see the current change according to Ohm's law. The sizes of the symbols in the equation change to match the circuit diagram.