Thermodynamics and Evolution on a Cellular and Planetary Level
Continued from: https://hubpages.com/education/Thermodynamics-and-Living-Systems
Planets evolve, and life on those planets evolves because of (among other things) the Laws of Thermodynamics: Matter, eternally in motion. Whether gas in a box or gas in interstellar space, the same laws apply, but they manifest differently at different scales of size and in different contexts. More on scale of size later.
According to the Second Law of Thermodynamics, a process (such as cell metabolism) can only happen without energy being added to the system if it increases the entropy of the universe (its environment). Measurement of Gibbs Free Energy is only concerned with what is happening within the system, but if a system absorbs or dissipates heat to its environment, its entropy debt has been paid. If it is a reversible process, it leaves total entropy unchanged. At the cellular level we are talking about chemical processes, and when researching these processes one will necessarily come across something called Gibbs Free Energy.
Gibbs Free Energy (G) is a measurement of the amount of energy in a system that can do work. The measurement of this energy informs us what happens to the energy in the system as it changes (delta G) from an initial state to a final one; what is released or absorbed, that is, the maximum amount of usable energy. In chemistry, reactants in the initial state become products in the final state. The value of this measurement will either be a positive or a negative number. If it is a negative number, then it is assumed a particular reaction can occur spontaneously, that is, without additional energy added to it. Positive numbers indicate the system becomes more ordered.
Test tube monkeys like to observe various reactions and notice they happen at certain temperatures and correspond to entropy and enthalpy changes. Enthalpy is energy stored in bonds, so a change of enthalpy is the difference between energies in the bonds between reactants and products. Constant pressure and temperature are assumed for purposes of calculation. The greater the temperature involved, the greater the change in entropy in relation to enthalpy.
Release of heat in a reaction (increase in entropy) makes the change in Gibbs Free Energy more negative and if it absorbs heat (decrease in entropy) the delta G is more positive. By comparing the change in enthalpy to the change in entropy we see whether spontaneity of reaction can happen at any temperature, only at a low temperature, only at a high temperature, only at a specific temperature, or not at all. For example, if the change in enthalpy (delta H) is negative and the change in entropy (delta S) is positive, the reaction will be spontaneous at all temperatures. If the opposite is the case, then the reaction will never be spontaneous (exergonic). In other words, for a reaction to occur energy must be added to the system. An exergonic, or spontaneous reaction, means that the reactants have more free energy than the products.
What does all this mean? Besides better living through chemistry, it means we are measuring motion! The purpose of this chapter is to help us to understand how thermodynamic laws of physics are related to chemistry and ultimately to biology: physics>chemistry>biology.
So taking these measurements, we see that a spontaneous reaction will occur, but we do not know WHEN the reaction will occur. Some reactions take place rather quickly and others may take an hour, a day, a year, or much, much longer. The Law of Maximum Entropy Production tells us that energy will flow along the path, or paths that allow maximum entropy to occur as soon as it can occur given the conditions. How fast the reaction occurs in terms of Gibbs Free Energy depends on the path(s) taken between initial and final states, and something called activation energy. Activation energy is the least amount of energy needed for a reaction to take place in a chemical system.
There is something called a reaction coordinate diagram which shows exergonic and endergonic reactions. Reactions that result in less energy are called exergonic and reactions that result in greater energy are called endergonic. We see that reactions can go forward or backwards. In other words, if endergonic in one direction, the reaction must be exergonic in the other, and vice versa. That is to say, if a reaction converts reactants to products in one direction then it must turn products into reactants in the other direction.
We see this in the breakdown and synthesis of ATP. ATP is how the cell pays its debt to entropy. If ATP is made in the cell by breakdown of glucose, then the exergonic reaction in reverse, or breakdown of ATP by hydrolysis, is the same magnitude only backwards. Keeping in mind that we are referring to a reversible process in “standard conditions” where temperature and pressure remains the same.
What happens inside a cell (in vivo) can be a result of non-standard conditions and vary significantly. The cell can alter the amounts of reactants and products so that forward directed spontaneity can occur. In other words, the cell acts on its own behalf to move away from equilibrium.
There’s something called chemical equilibrium. If we start with all reactants, conversion to products occurs rapidly but the reverse can not happen because there are no products. Once there are some products, the reverse reaction can begin to occur. When the forward and reverse reactions are happening at the same rate, chemical equilibrium is reached. Reactions continue, but there is no change in the amounts of products and reactants. Since all systems move towards equilibrium, the free energy gets lower and lower, and eventually the system can do no work.
A cell reaching equilibrium will eventually die without additional energy because, in compliance with thermodynamics, it will be at its lowest energy (stable) state and it will require work to move away from equilibrium. Luckily a cell is not an isolated system! Cells are good at importing reactants and exporting products in order to stay out of equilibrium. They can also manipulate metabolic pathways where reactions can domino, or in other words, one reaction is used to push (or pull) another reaction. The product of one reaction is then the reactant for the next reaction. This is called reaction coupling.
Thus, we can see that all systems, including self organizing systems move towards equilibrium, but living self-organizing systems can move against or with the path of least resistance. No wonder Mother Nature maximizes the amount of life in any given area. In fact, with an eternity of matter in motion, where life is possible, life is inevitable.
While the Second Law of Thermodynamics is about keeping the books balanced by creating end-directed processes, the Law of Maximum Entropy Production ensures that order is reached as quickly as possible given the conditions. Since living systems are better at this, then non-living systems, life will always abound where possible.
Thermodynamics underlies the genesis and evolution of what is known as perception-action cycles. In cognitive systems the perception-action cycle is the flow of information between a living system and its environment using sensory guided behavior working towards a specific goal. Without an interconnecting physical mechanism between the organism and its environment, it appears as magic, and indeed, Shannon’s information theory and other so-called theories incorporate the use of the word entropy in a non-physical, magical sense.
Cognition and perception, along with the accompanying sensory systems, were inevitable given the Laws of Thermodynamics. Because a living organism can make choices and move against gravity and against or with the path of least resistance, ordered flow of energy and dissipation potentials occur faster. In other words, the quality of movement of living systems is superior to that of non-living systems. Rather than the physical world acting by way of some deterministic mechanism and biology being autonomous, both physics and biology stand on the same principles of thermodynamics.
Living things, then, are part of a larger system which includes its environment. End-directed behavior of living systems then has its origin in physical laws. Survival within the cell of an organism and for the organism itself depends on the flow of energy between its constituent parts and with the environment. The only way a living thing can live is to eat, and the only way it can eat is to move. The Second Law of Thermodynamics is about dissipation of energy, not restoring it, but the perception-action cycles help to dissipate energy thereby increasing the rate of entropy production in the living system’s environment.
Evolution on a planetary scale shows how atmospheric oxygen created by diverse living things increased entropy, as does fire and rust. There are basically two types of oxidation, slow and fast. Rust and fire. Look at the history of oxygen, rust, and fire on Earth, and note the importance of these processes. Mother Nature seeks balance, and among other things, uses oxidation to do this. With the bare essentials, (exogenous) antioxidants and free radicals in a living system will add to it its own (endogenous) antioxidants and free radicals. It’s impossible to separate living from non-living in the planetary system.
Increase in atmospheric oxygen helped move the planet away from equilibrium by transforming the redox state of the planetary system. The planet was reducing when life began, gradually moved to mildly oxidative and presently is in a highly oxidative state. This shows a reduction in entropy (a more ordered state) in the planetary system over billions of years. Of course, this means that entropy was increased somewhere external to the system.
There are many examples of increasing order and reducing entropy from the first bacteria able to photosynthesize sunlight and using waste products from outgased volcanic compounds, to cyanobacteria which linked light to water, to Earth’s reservoirs of sulphur and iron combining with oxygen.
Increased order on Earth means increased entropy elsewhere, but where does it end? Where is entropy’s debt paid on a universal scale?
Conservation of energy means that spin angular momentum is being transferred to the moon, so the moon’s orbit is higher and its orbital speed is decreasing. The moon will stop spinning at the same rate that it is orbiting the earth. The earth will eventually stop spinning and the moon and earth will face each other with one side. When two bodies are bound gravitationally like the earth moon system, they will eventually synchronize their rotational and orbital spin.
The Solar System will likewise be affected, and eventually the galaxy, and so on….but where does it end?
It doesn’t! We are ultimately talking about matter in motion. Since matter in motion is eternal, and since everything is interconnected by EM ropes, the feedback and feed forward mechanism insures that all objects will eventually disassemble into their constituent H-atoms, then reassemble as something else, and then disassemble again, and reassemble again…forever.