[Iamyourfather]

I have answered these questions. What do you think of my answers?

Question: http://www.flickr.com/photos/85189286@N06/8192442850/in/photostream/lightbox/

Answers:
4. 
a)
The neuron and the astrocyte cell are the manipulation of a system. The second law of thermodynamics states that the entropy of closed systems never decreases, because closed systems spontaneously evolve towards thermal equilibrium -- the state of maximum entropy.

The implementation of a gap junction (the ‘fish trap’) between the two cells allow dye molecules to move in a unidirectional manner. This gap junction therefore allows the molecules to move from a large volume to a smaller volume, which will require movement from a lower to greater concentration. An increased concentration within a closed system will decrease entropy. This is because molecules pack closely together and have less space to move.
This theory can be expressed into an equation:
 S = S° - Rln(c)
   
S is the entropy of the solution, S° is the standard entropy at 1M concentration (or 1 atm partial pressure), and c is the actual concentration (or actual partial pressure, for a gas). If the concentration increases the entropy decreases.

b) Small molecules are more likely to pass through a ‘fish trap’ bi-directionally because they are significantly smaller in size -   A ‘fish trap’ model is where a gap junction (i.e. a gap somewhat like a fish trap) separates a system. A ‘fish trap’ is comprised of a two pores located on opposite regions of the ‘trap’, where one pore is smaller than the other. The larger pore is the opening in which many moving objects can pass. The smaller pore will only allow one or a limited few objects (depends on the size of the diameter) to pass.

Small molecules can pass through the larger pore very easily; however it may take a longer amount of time for small molecules to pass through the smaller pore (bi-directionally) if they accumulated themselves by it. A/a few fish may by be able to pass through the trap in a bi-directional manner however due to fish being large in size, many fish will struggle to pass through the smaller pore at once. It therefore will take a significantly longer time for fish to escape than all small molecules.

c) Kinetic energy from a fish will allow it to move. You could say the fish has high entropy as it moves in arbitrary directions until it comes into contact with a fish trap. The design of a ‘fish-trap’ model is mentioned in 4b). The larger pore will allow a supple amount of fish to pass through the pore at one time. This is because its diameter will be greater than the size several fish. The size of the larger pore will also increase the chance of fish coming into contact with the trap and moving through it. The smaller pore is built so that one or a small number fish at a time can pass through it. The accumulation of trapped fish on the other side of the system will prevent the fish from escaping because a high concentration of fish cannot pass through the smaller pore at one time. Moreover as fish move in arbitrary directions the chances it will leave the other side of the system through a small pore are small.
d)  Molecules move through cells through protein ion channels between each cell. Rather than a ‘fish trap’ gap junction, the gap junction will have pores that are parallel in size. In order to increase entropy many dye molecules will move through the neurone (from a high concentration of dye molecules to a low concentration) in one direction.

[Babcock_Hall]

With respect to your answer for d), I don't see why transport would be unidirectional.

[Iamyourfather]

With respect to your answer for d), I don't see why transport would be unidirectional.

According to the 2nd law of thermo the molecules will move from a high concentration (point of injection in cell) to a low concentration (end of the neuron). So wouldn't the molecules move in one direction and eventually fill the volume of the neurone?

Do you suggest any other ideas?

[Iamyourfather]

With respect to your answer for d), I don't see why transport would be unidirectional.

Is this clearer?:

d)  Molecules move through cells through protein ion channels between each cell. Rather than a ‘fish trap’ gap junction, the gap junction will have pores that are parallel in size. In order to increase entropy dye molecules will be injected into the astrocyte and will move through the neurone from a high concentration (point of injection) of dye molecules to a low concentration (end of neurone) in one direction. A nerve impulse is propagated without decrement (i.e. it does not get smaller as it moves further away from the point of origin). This does not violate the Second Law of Thermodynamics, because the energy for the conduction comes from within (not from the stimulus).


The experiment manipulates resting potential so the system will eventually reach stability. The equilibrium state of a system (i.e., the most stable accessible state) is the one that maximizes the entropy of the system (subject to any constraints placed on the system).