AP Biology - FRQ (Laws of Thermodynamic/ Entropy)

Question

1. Use the first and second laws of thermodynamics, explain how living systems are able to use anabolic processes without violating the 2nd law of thermodynamics by building ordered molecules from disorganized atoms. 

Answer 1

Anabolic processes are endergonic or energy requiring processes where larger molecules are made from smaller molecules. A classic example is the formation of proteins from amino acids. The 1st law of thermodynamics states that energy can not be created or destroyed and is the law of conservation of energy and in respect to living systems, which can be thought of as "closed systems" process like the formation of larger molecules from smaller ones occur all the time and require something to "help" this occur. Then, there must be something that comes from outside the living organism (system) that comes in and allows anabolism. A good example of this maybe a small single celled green algae that uses photosynthesis. This single cell receives photons (from sunlight) to activate photosynthesis where one of the products of photosynthesis is ATP. ATP is a very important highly energic molecule that living systems basically depend upon for any cellular process to occur. Thus, we can easily talk about anabolism and not have to worry about the 1st Law. For the 2nd Law where entropy is increasing always and anything seems to be always become less, yes less, disorganized in closed systems like a cell. Then, if dis-organization is increasing and anabolic process need energy to make molecules form smaller molecules, how does a cell make something as complex as a large-multi-subunit protein that when in its final form, can be actually very organized and the process itself very complex, coordinated, and relies certain things to be in place at a specific time for any of this to occur? Well, living systems, especially small ones, like bacteria, are very good at be very efficient at making things. Thus, we can say that a cell can generate a larger molecule from smaller, similar ones with an input of energy, and as to whether or not organization or entropy changes during and as a result of the process is something "separate" from the closed system such that certain conditions and parameters will favor the input of energy that is required when a process like making a larger molecule from smaller ones is coupled, and this is the key term, coupled, or associated with, another process that favors something else where the reaction is still thermodynamically favorable, and after the reaction, the dynamics of the cell and parts of the cell that was used in that process, is still available and can be thought of, or, all of times, actually is, in a disorganized state. Hence, is not smaller, separate, amino acids much more disorganized than a mature protein? Good luck, John