The art (kunst) that must be added to the science (wissenschaft) of macroscopic analysis is picking the right compartments and the right "entities" to follow.But one must measure what is defined, or define what is measured!
What goes in, plus what is made, minus what goes out, is always what accumulates.All basic representations are useful if properly reinterpreted:.Macroscopic Problems: Cell Aggregates, Organs When related chemical species are considered: finite-rate chemical transformations define compartments, too.When its "organelles" must be considered:.cyclic and sequential behavior is concealed in cohort-scale measurements.Steady state means, at the most fundamental level, no change in accumulation.Steady state is a property of the system and the frame of reference.All variables of interest have the same value at all moments of observation.Expressed in terms of "Hill Functions":.Desirable biological function that supports homeostasis.May be important – especially in neural cells.Models exist for both facilitated (not active) and active transport.Unlike enzymes, permeases do show reversible behavior.Can be regarded as enzymes that facilitate transport rather than reactions.Enzymes are catalysts – they never change an equilibrium– only the rate.Enzyme reactions are usually irreversible.
In processes involving both reaction and transport, rate-limiting step may be of either type.Others equilibrate either with reactants or products of rate-limiting processes. A few reactions among many are rate limiting.Reaction: equilibrium, power-law, enzymatic.Accumulation with and without volume change.Input and output via convection, permeation – passive, permease-driven, active and coupled transport.Compare with path-particularized systems. Material – mass, energy Molecular delivery is particularized by packaging what is to be delivered (message or material) so that only intended recipients are reached.All larger-scale entities acquire their ultimate meaning and explanation in molecules.Atoms acquire meaning only in molecules.They are the most important elements in biological systems.Transport and Rate Phenomena in Biological Systems Redux