Biophysics · MU Sofia

7. The entropy in open systems: validity of the laws of thermodynamics in living systems. The change of entropy in an open system. Steady state and thermodynamic equilibrium

Covers how thermodynamic laws apply to living systems treated as open, non-equilibrium systems that exchange energy and matter with their surroundings. It then lists applications such as energetics, membrane transport, membrane potentials and biopolymers, followed by restrictions on living processes. The entropy balance equation is given, with its internal production and external exchange terms, and the note closes by explaining steady state and thermodynamic equilibrium.

Inside: 1 section · 3 labelled pictures · 2 formulas · 13 flashcards · 3 min

Topic 7 of 26 in the MU Sofia syllabus for Biophysics (Dental Medicine, Year 2). The free AceMed note covers it in 1 section, about 472 words (3 min of reading), with 13 flashcards.

In this note

  1. The entropy in open systems

The entropy in open systems

Validity of the laws of thermodynamics in living systems. The change of entropy in an open system. Steady state and thermodynamic equilibrium.

The living systems are open thermodynamic systems, which exchange both energy and matter with their surroundings (as in any other open system). The entropy S of the living systems may either increase or decrease depending on the direction of energy and heat exchange between the living organism and the surrounding medium.

As open non-equilibrium thermodynamic systems, the living systems obey the laws of non equilibrium thermodynamics, and in cases where their state is very close to equilibrium, they also obey the laws of equilibrium thermodynamics

Living systems maintain a high degree of order and counteract the tendency to disorder by utilizing energy from the surrounding medium.

Applications of thermodynamics to living systems:

Thermodynamics has several extremely important applications for description of the processes taking place in living systems.

  1. 1. Processes of energy transformation and energetics of biochemical reactions.
  2. 2. Transport processes of substance (membrane transport).
  3. 3. Electrical potentials (membrane potentials).
  4. 4. Thermodynamics of biopolymers (proteins, nucleic acids)

Thermodynamic restrictions on the processes in living systems.

  1. 1. The second law of thermodynamics requires the entropy production during any non-equilibrium processes taking place in living systems to always be a positive quantity
  1. 2. The functional state of the living organisms can only be supported at the expense of energy from the surrounding medium.
  2. 3. The energy flow through the (living) system should be big enough, so that the work performed by the system should ensure, on the average, an entropy outflow from the system to the environment, which is bigger or at least equal to the entropy produced by the system.

The living organisms are heterogeneous, non-equilibrium open systems capable of self-organization, self-regulation and reproduction. They come into being and grow in irreversible processes of individual and evolutionary development as a result of: CONSUMPTION OF FREE ENERGY FROM THE SURROUNDING MEDIUM.

Their death and decay are accompanied by the establishment of THERMODYNAMIC EQUILIBRIUM in the system and the surrounding medium.

While the laws of thermodynamics cannot be broken in the processes taking place in living systems, these laws only explain particular features in the functioning of the living systems,

but they cannot predict and explain phenomena such as the origin and development of life on earth in its entirety.

Equation of entropy balance:

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