On Aug 12, 12:21 pm, Jarek Duda gmail.com> wrote:
rst spot it seems to be against classical thermodynamics -

You need a temperature difference.
The hot iron emits photons, but it also absorbs photons. If the
iron is in an equilibrium environment, the two processes are of equal
magnitude. Look up black body radiation. This has been studied plenty
of times.
What you are proposing is a biological thermocouple. Thermocouples
don't work unless one side of the thermocouple is at a different
temperature than the other side. The power output of the thermocouple
is proportional to the temperature difference. This is why
thermocouples really aren't used for power. Their output is too small.
The thermocouple emits and absorbs photons just like your hot iron.
However, the difference in metals plus the difference in temperature
causes a current to flow.
Thermocouples are used in regulators. Air conditioning used to
rely on thermocouples to measure temperature. One side was exposed to
outdoor conditions and one side to indoor conditions. I think air
conditioners now use temperature sensitive resistors or diodes, but I
am not sure. In any case, your organism would have to couple itself to
two heat reservoirs of different temperature. The bigger the
difference, the better.
In any case, the first place to look for a biological
thermocouple may be as a temperature sensor for homeostasis. However,
I think there are far better ways for an organism to measure
temperature.
The trick is to use a resonance

People have looked long and hard for a way to turn internal
energy (i.e., heat energy) into work. The second law of thermodynamics
forbids it, but people look anyway. Which is fine. However, no one has
found a resonance that beats the second law of thermodynamics.
In a way, Brownian motion is an example of heat energy turning
into sound. Brownian motion has been examined as a potential power
source. However, the problem is similar. The work performed by
Brownian motion is dissipated by friction at the exact same rate of
power if the system is at equilibrium. When the entire system is the
same temperature, the system is in equilibrium. The very act of taking
energy from the Brownian motion evens out the temperature. Eventually,
the entire system equilibrates at the same temperature and the power
output stops.

How does a molecule resonance? Resonance is a noun. Nothing can
resonance, they can only resonate. I suspect you mean something else,
but don't know the English word.
You probably mean an enzyme that speeds up the reaction binding
ADP to phosphate. The problem is that enzymes speed up the reactions
going both ways. An enzyme that speeds up the binding of ADP and
phosphate speeds up the splitting of ADP from phosphate. Therefore, an
equilibrium is reached. Enzymes never extract energy from a reaction
if the system is at equilibrium. If the system is out of equilibrium
anyway, but occurs very slowly, an enzyme speeds it up. However, the
thermodynamics of enzymes have been studied for ever and aye. They
can't be used to extract heat.
At least, not so far. You are welcome to try looking for the
perpetual motion enzyme, but I don't think your chances are very good.
As Mel Brooks said when asked what his ambition was, "My ambition is
to never die. Historically, my chances of achieving it don't look
good."

I respectfully disagree. Some reactions are irreversible. Pick
up a chemistry textbook.

It may not be doable.
However, I wonder if a biological thermocouple exists for
regulation. You did get me thinking...