Introducing Biological Energetics: How Energy and Information Control the Living World

Activation energy and reaction rate. The activation energy of a chemical reaction is closely related to its rate.

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Specifically, the higher the activation energy, the slower the chemical reaction will be. This is because molecules can only complete the reaction once they have reached the top of the activation energy barrier. The higher the barrier is, the fewer molecules that will have enough energy to make it over at any given moment. Why do some molecules have more energy than others?

How Energy and Information Control the Living World

At a particular temperature, individual molecules in a sample will have a range of different kinetic energies — temperature is just an average value. This means that some fraction of molecules in a population will be able to make it over an activation energy barrier, but if the barrier is high, this fraction may be tiny. In this case, the reaction will be very slow: Many reactions have such high activation energies that they basically don't proceed at all without an input of energy.

For instance, the combustion of a fuel like propane releases energy, but the rate of reaction is effectively zero at room temperature. To be clear, this is a good thing — it wouldn't be so great if propane canisters spontaneously combusted on the shelf! Once a spark has provided enough energy to get some molecules over the activation energy barrier, those molecules complete the reaction, releasing energy.

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The released energy helps other fuel molecules get over the energy barrier as well, leading to a chain reaction. Most chemical reactions that take place in cells are like the hydrocarbon combustion example: The process of speeding up a reaction by reducing its activation energy is known as catalysis , and the factor that's added to lower the activation energy is called a catalyst.

Download the original article for free at http: Retrieved August 29, from Wikipedia: An introduction to metabolism. Because energy flows at all scales, from the quantum level to the biosphere and cosmos , energetics is a very broad discipline, encompassing for example thermodynamics , chemistry , biological energetics , biochemistry and ecological energetics. Where each branch of energetics begins and ends is a topic of constant debate. For example, Lehninger , p. In general, energetics is concerned with defining relationships to describe the tendencies of energy flows and storages under transformation, defined here as phenomena which behave like historical invariants under repeated observations.

When some critical number of people have observed such invariance, such a principle is usually then given the status of a ' fundamental law ' of science. As in all scientific inquiry, whether a theorem or principle is considered a fundamental law appears to depend on how many people agree to the proposition. The ultimate aim of energetics therefore is the description of fundamental laws.

Philosophers of science have held that the fundamental laws of thermodynamics can be treated as laws of energetics, Reiser , p. By continuing to more accurately describe these laws, energetics aims to produce reliable predictions about energy flow and storage transformations at any scale.

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Energetics has a controversial history. Some authors maintain that the its origins may be found in the work of the ancient Greeks, but that the mathematical formalisation began with the work of Leibniz. Richard de Villamil said that Rankine formulated the science of energetics in his paper Outlines of the Science of Energetics published in the Proceedings of the Philosophical Society of Glasgow in Mach subsequently developed the study, and by the late s energetics was understood to be incompatible with the atomic view of the atom forwarded by Boltzmann 's gas theory.

Proof of the atom settled the dispute but not without significant damage. In the s Lotka attempted to build on Boltzmann's views through a mathematical synthesis of energetics with biological evolutionary theory.

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Lotka proposed that the selective principle of evolution was one which favoured the maximum useful energy flow transformation. This view subsequently influenced the further development of ecological energetics, especially the work of Howard T. De Villamil attempted to clarify the scope of energetics with respect to other branches of physics by positing a system that divides mechanics into two branches; energetics the science of energy , and "pure", "abstract" or "rigid" dynamics the science of momentum.

According to Villamil energetics can be mathematically characterised by scalar equations, and rigid dynamics by vector equations. In this division the dimensions for dynamics are space , time and mass, and for energetics, length , time and mass Villamil , p.

This division is made according to fundamental suppositions about the properties of bodies, e. In Villamil's classification system, dynamics says yes to 1 and no to 2, whereas energetics says no to 1 and yes to 2.

Activation energy

Therefore, in Villamil's system, dynamics assumes that particles are rigidly fixed together and cannot vibrate, and consequently must all be at zero kelvin. The conservation of momentum is a consequence of this view, however it is considered valid only in logic and not to be a true representation of the facts Villamil, p. In contrast energetics does not assume that particles are rigidly fixed together, and thus are free to vibrate, and consequently can be at non-zero temperatures.

As a general statement of energy flows under transformation, the principles of energetics include the first four laws of thermodynamics which seek a rigorous description.

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