Question

It has been argued by those who do not believe in evolution that a cell could not evolve because such an occurrence would go against the idea that there is a constant tendency in the universe towards spontaneous disorganization (an increase in entropy). How would you counter that argument?

Answer 1

No doubt, the entropy criterion explains that a reaction will be spontaneous when there is increase in entropy i.e increase in degree of randomness. But if the system, in which reaction is going on, is a non isolated system and it has connection with surrounding such as it can exchange energy or mass with the surrounding, we have to see entropy change not only in the system but also in the surrounding. Consider that energy is lost by the system, it goes into surrounding, then because of this the entropy of system will decrease but the entropy of surrounding will increase. Now if the total entropy change of both system and surrounding is positive, the reaction will be spontaneous even though entropy change of the reaction is negative, it means the total entropy change of system and surrounding should increase to have a reaction as spontaneous.

A non spontaneous process in which total entropy of system and surrounding together decreases, may also take place when a spontaneous process occurs simultaneously along with that non spontaneous process (coupling of reactions). This may be explained on the basis of Gibbs energy change for the coupled reactions. For a reaction to be spontaneous the Gibbs energy change for the system must be negative. When two reactions occur simultaneously they are said to be coupled. In that condition, the Gibbs energy change of two reactions will be added and if the total Gibb's energy change of both the reaction is negative then both the reaction become spontaneous. It means, the non spontaneous process with less positive Gibbs energy change, can occur with the help of the spontaneous process with high negative Gibbs energy change. The overall Gibbs energy change for both the processes together will be negative.

Now we talk about the example of a cell which is evolved in the nature. It is a complex system which is formed by so many spontaneous reactions and nonspontaneous reactions occurred in sequence. If you consider the cell as a non isolated system then you have to consider total entropy change of the system and surrounding which will be positive for many of these reactions thats why these reactions occur spontaneously. The non spontaneous reactions occur with the help of spontaneous reactions which are going on simultaneously that's why a cell evolve in the nature spontaneously.