What thermodynamics can tell us about Living Organisms?

Classical thermodynamics Closed system A system, over the border of which only energy can be transmitted. Open system A system, over the border of which both energy and mass can be transmitted. Ecosphere is e closed system. All living systems are open. Classical thermodynamics Any physical system will spontaneously approach a stable condition (equilibrium) that can be described by specifying its properties, such as pressure, temperature, or chemical composition. If the external constraints are changed, then these properties will generally alter. The science of thermodynamics attempts to describe mathematically these changes and to predict the equilibrium conditions of the system. But living systems are open far from equilibrium systems

Equilibrium Non equilibrium Arrow of TIME Being Becoming reversibility irreversibility one can never step in the same river twice (Heraclitus) No temporal direction Arrow of TIME "What then, is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know." (St. Augustine) The microscopic world is time reversible, the macroscopic world is not

Entropy determines the arrow of time Thermodynamics laws The first law states that energy can not be destroyed nor created. The second law (often referred to as the 'entropy' law) states that the quality of energy is degraded in each spontaneous change.

entropy measures the dispersal of energy: how much energy is spread out in a particular process, or how widely spread out it becomes. W=number of substates W1 W2 W2>W1 It is not impossible for events to reverse themselves, just very, very, very improbable

Natural systems do not exist in equilibrium state, but they can exist in steady state What is a steady state? Some examples: So…what is the difference between equilibrium and steady state?

Sout>Sin Irreversible thermodynamics focuses on the system Equilibrium state: Steady state: Sout>Sin A sink for entropy is very important!

But quality (i.e. entropy) of this energy must be different High quality energy must come into the system and low quality energy must come out

Low entropy High entropy

Ecosphere is a closed system in touch with a hot source (the SUN) and with a cold sink (the space) number of subsystems extremely high number of entropy producing processes (i.e. natural phenomena) extremely high Hot (5800 K) cold (3 K)

In linear conditions σ reaches a minimum at the steady state A steady state may exist only when at least one gradient is kept constant The gradients are referred as thermodynamic forces and they produce thermodynamic fluxes. If non-equilibrium systems are close to the equilibrium state, the fluxes are in general linear functions of the gradients. Some examples: Fourier’s law Fick’s law Ohm’s law Poiseulle’s law In linear conditions σ reaches a minimum at the steady state

In a non-equilibrium state When the gradients are very wide, relationships between forces and fluxes are not linear anymore. The only general rule about the solution of non-linear differential equations is that there are no general rules, but funny things can happen when linearity is lost! macroscopic order In a non-equilibrium state may appear The appearance of Bénard cells is an example of order out of chaos. The local heating causes entropy to increase, but the density inversion induces complex and non-linear behaviour. Convection cells that arrange into a regular hexagonal lattice are an example of dissipative structures.

Negative entropy (negentropy) Schrödinger introduced the concept when explaining that a living system (a dissipative structure) exports entropy in order to maintain its own entropy at a low level. By using the term negentropy, he could express this fact in a more "positive" way: a living system imports negentropy and stores it. order Sin Sout Dissipative structures are fed by a flow of negentropy wich means compatibility between the processes and the environment that is supporting the structure. Coevolution of natural systems is at the basis of their compatibility.

complex molecules (low entropy matter) What is the thermodynamic peculiarity of photosynthetic organisms? Photosynthetic organisms hot photons (low entropy energy) CO2, H2O, simple molecules and ions (high entropy matter) Heat (high entropy energy) complex molecules (low entropy matter) Photosynthetic organisms are fed by light negentropy becoming in turn chemical negentropy for chemotrophs

complex molecules (low entropy matter) Chemotrophs are not able to use light negentropy Heat (high entropy energy) Chemo heterotrophs complex molecules (low entropy matter) CO2, H2O, simple molecules and ions (high entropy matter)

Mantaining organization requires deS<0 (Sout>Sin) At the steady state: Energy and matter Energy and matter Energy and matter Energy and matter Energy Entropy matter matter Produced entropy Q Produced entropy matter Q hv matter IN OUT IN OUT Photoautotroph chemoheterotroph

How photosynthetic organisms are able to exploit hot photons negentropy? Chemistry Physics Photosynthetic organisms are able to capture the electron from the excited state. Thanks to this, photons are converted in chemical energy.

Hope you are now convinced that: 2nd law is not in contrast with self-organizing living systems and ecosystems We cannot be isolated systems Sinks are as important as sources Photosynthetic organisms are smart We should love photosynthesis!