Thermodynamics in Biology

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What is meant by work done by the system and work done on the system, in biological systems?

In physics related systems however:
Work is simply a force multiplied by the distance moved in the direction of the force. A good example of a thermodynamic system that can do work is the gas confined by a piston in a cylinder. If the gas is heated, it will expand and push the piston up, thereby doing work on the piston. If the piston is pushed down, on the other hand, the piston does work on the gas and the gas does negative work on the piston. This is an example of how work is done by a thermodynamic system.
 

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  • #2
Andrew Mason
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What is meant by work done by the system and work done on the system, in biological systems?

In physics related systems however:
Work is simply a force multiplied by the distance moved in the direction of the force. A good example of a thermodynamic system that can do work is the gas confined by a piston in a cylinder. If the gas is heated, it will expand and push the piston up, thereby doing work on the piston. If the piston is pushed down, on the other hand, the piston does work on the gas and the gas does negative work on the piston. This is an example of how work is done by a thermodynamic system.
In thermodynamics work (W) is macroscopic mechanical work performed by a system of molecules in moving between states of thermodynamic equilibrium. It is not difficult to find examples of biological systems doing work. It is a bit more difficult to provide examples of work being done on such systems. Living systems are essentially heat engines to do macroscopic mechanical work.

A biological system doing work: The human body can mechanically lift a weight for example. The muscle movement required to lift a weight is the result of thermodynamic processes taking place in muscle cells that convert internal (chemical) energy into heat flow. The human heart can be thought of as a thermodynamic system that uses internal (chemical) energy in its cells to create heat flow that causes the heart muscle to contract and expand, pumping blood through the body.

Doing work on a biological system: By applying CPR to a stopped human heart, one does work on that system and causes the heart to pump blood.

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  • #3
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Sorry for the late response. So basically for biological systems work is being done by the system and rarely on the system.
 
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Andrew Mason
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I would not say "rarely", because work is being done on biological systems all the time. For example, when a mammal infant draws milk from its mother it is doing work on a biological system; or when a python squeezes its prey; or when air currents lift a bird; or when a wind gust breaks a tree branch; or when a tree root pushes soil to grow roots (the soil being a sort of biological system); etc.

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