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Transcript
What thermodynamics can tell us about Living Organisms? Closed system A system, over the border of which only energy can be transmitted. Ecosphere is e closed system. All living systems are open. Open system A system, over the border of which both energy and mass can be transmitted. 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 Being Becoming reversibility irreversibility No temporal direction one can never step in the same river twice (Heraclitus) 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: dX i 0 dt dS 0 dt So…what is the difference between equilibrium and steady state? Irreversible thermodynamics focuses on the system dS sys d i S d e S Equilibrium state: Steady state: Sout>Sin di S d e S 0 di S 0 d e S 0 di S 0 dt di S d e S di S 0 dt A sink for entropy is very important! di E dE st 0 0 1 law dt dt de E 0 Ein Eout dt 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) 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 di S Ji X i 0 dt i In linear conditions σ reaches a minimum at the steady 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. dS 0 de S di S 0 Sin order 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. What is the thermodynamic peculiarity of photosynthetic organisms? Heat (high entropy energy) hot photons (low entropy energy) Photosynthetic organisms CO2, H2O, simple molecules and ions (high entropy matter) dS sys d e S di S di S 0 ; d e S 0 d e S de S( matter ) de S( energy ) d e S( matter ) 0 de S( energy ) 0 , complex molecules (low entropy matter) Photosynthetic organisms are fed by light negentropy becoming in turn chemical negentropy for chemotrophs d e S( energy ) d e S( matter ) Chemotrophs are not able to use light negentropy Heat (high entropy energy) complex molecules (low entropy matter) Chemo heterotrophs CO2, H2O, simple molecules and ions (high entropy matter) de S de S( matter ) de S(energy ) 0 de S( matter ) 0 and de S(energy ) 0 Mantaining organization requires deS<0 (Sout>Sin) Energy and matter matter Q Produced entropy hv IN Energy and matter matter Energy and matter Produced entropy E n t r o p y At the steady state: Energy and matter E n e r g y matter Q OUT Photoautotroph matter IN OUT chemoheterotroph How photosynthetic organisms are able to exploit hot photons negentropy? Physics Chemistry 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!