Transcript any physical system, whether or not it can exchange energy and

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!