Living Systems as Energy Converters (eBook)

M.J. Allen, R. Buvet, J.-P. Massue (Herausgeber)

eBook Download: PDF | EPUB

2013 | 1. Auflage
358 Seiten
Elsevier Science (Verlag)
978-1-4831-6378-9 (ISBN)

Infos

Living Systems as Energy Converters documents the proceedings of the European Conference on Living Systems as Energy Converters held in Pont-a-Mousson, France on October 18-22, 1976. This book is organized into three main topics-energy in biological molecules; biological membranes as energy transducers; and energy in cells, organisms, and populations. In these topics, this compilation specifically discusses the energetic evolution of complex networks of reactions; protein ß-structure and the molecular evolution of biological energy conversion; and structure and function of ATP synthase. The calcium transport in biological membranes; conversion of solar energy into energy-rich phosphate compounds; and energy conservation in photosynthetic electron transport of chloroplasts are also deliberated. This text likewise covers the direct conversion of radiant into electrical energy using plant systems; energy budgets in natural and agricultural ecosystems; and recycling of excess carbon dioxide from fossil energy conversion by plants. This publication is intended for biologists and physical-chemists, including students concerned with the study of living systems as energy converters.

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Living Systems as Energy Converters documents the proceedings of the European Conference on Living Systems as Energy Converters held in Pont-a-Mousson, France on October 18-22, 1976. This book is organized into three main topics-energy in biological molecules; biological membranes as energy transducers; and energy in cells, organisms, and populations. In these topics, this compilation specifically discusses the energetic evolution of complex networks of reactions; protein -structure and the molecular evolution of biological energy conversion; and structure and function of ATP synthase. The calcium transport in biological membranes; conversion of solar energy into energy-rich phosphate compounds; and energy conservation in photosynthetic electron transport of chloroplasts are also deliberated. This text likewise covers the direct conversion of radiant into electrical energy using plant systems; energy budgets in natural and agricultural ecosystems; and recycling of excess carbon dioxide from fossil energy conversion by plants. This publication is intended for biologists and physical-chemists, including students concerned with the study of living systems as energy converters.

Textauszug

INTRODUCTION: LIVING SYSTEMS AS ENERGY CONVERTERS

George PORTER,     Davy Faraday Research Laboratory of The Royal Institution, 21 Albemarle Street - LONDON WLX 4 BS

The system of mechanics developed just over four hundred years ago by Galileo, Newton and their successors, all embracing as it was in many respects, did not include the concept of energy as we understand it today. Since living systems can only survive through their property of energy conversion and the utilisation of the energy derived from outside sources, the science of mechanics contributed almost nothing to the understanding of life.

The basic physical laws which are essential to such an understanding are those of thermodynamics, developed in the mid-nineteenth century by Sadi Carnot, a French engineer who in 1824 discovered what we now call the second law and by J.R. Mayer and James Prescott Joule who independently arrived at the first law, the law of energy conservation, around 1840. It is interesting to recall that Meyer, who was a physician, was led to the idea through a consideration of animal heat and work. In spite of earlier work by Benjamin Thompson, Davy and others, the connection between force, energy, work and heat had, up to this time, been hopelessly confused. This had not altogether discouraged the inventive and practical men of the time who had nevertheless managed to invent engines for the conversion of heat into work, albeit inefficient ones, and it has been said that science owes more to the steam engine than the steam engine owes to science.

In the absence of an understanding of thermodynamics it is not surprising that living systems seemed to be fundamentally different from non-living systems obeying the laws of mechanics. The origin of life and the growth of a living organism, (the resurgence of life in the Spring) and the appearance of complex order from chaos and disorder was a miracle, the explanation of which seemed to lie beyond natural laws. The supernatural world of Gods and forces beyond our ken were almost universally accepted. Today, although some may feel a need to cling to these beliefs for other reasons, the “mystery” of life is no longer in any conflict with the laws of nature… no vis vitae is needed to create it or maintain it, other than the sun.

The second law of thermodynamics tells us that, although energy as a whole is conserved (by the first law), energy appears in several forms which are not always interconvertible. We may speak of high-grade energy and low grade energy, depending on the amount of randomness, disorder or entropy which is associated with that energy.

The highest grade of energy, which has no entropy or disorder associated with it, is called free energy - “free” because it is free to be converted entirely into useful work. Heat energy is only partly free to be converted into work and when heat is transferred from one body at temperature T1 to another at the lower temperature T2, the fraction of heat transferred which is free to do work is simply (T1-T2)/T1. This is a maximum value and, in practice, the fraction will be less. Heat at high temperature is therefore a higher grade of energy than heat at a low temperature because a higher proportion of it is free to do work. The total energy change in a chemical or biological process is also different from the free energy change or the amount of work which can be derived from that change.

In all natural processes, spontaneous changes in nature, some high grade energy is degraded and this is an irreversible event… a running down of the universe. Put another way, the second law appears as a common observation that, if left to themselves, things become more mixed-up, disordered… the entropy increases spontaneously. In thermodynamic terms “In every spontaneous process in a closed system, the total entropy of the system increases”.

What, then, of our life system on earth? Here we see the most wondrous examples of order increasing, apparently spontaneously, in the process of evolution as well as in the detailed processes of growth and development of living things. It occurs even in the increasing order and complexity of our social organisation, though the future of this process is beginning to look a little less secure. Does this imply that living systems do not comply with the laws of thermodynamics? Of course not; the explanation is to be found in the words “in a closed system” carefully included in the last paragraph. There is no difficulty in increasing the order and decreasing the entropy of a system provided we can pump free energy into the system from outside. This is how life evolves and survives, and the source of free energy - of negative entropy - is the sun. Its importance has probably always been recognised by those who contemplated the problem of life, as it was by the authors of the book of Genesis when they described in the third verse, how, before any life appeared God said “Let there be light”. Without that light on the first day the rest could not have happened.

The radiation of the sun approximates to that of a black body at 6000 °K so that its energy, transferred to our earth at about 300 °K, is high grade. Even after making allowances for scattering over all angles, more than 75% can, in principle, be converted into useful work. But it has some disadvantages… it is intermittent and, to ensure a constant supply of energy, some storage method has to be found. Furthermore, if we are to use it efficiently, the sun’s energy must be converted before it is degraded to low temperature heat (except for the limited amount of energy which may be needed in this form). The energy covers a wide band of wavelengths and the collector which is used should not only collect as many wavelengths as possible but use each wavelength efficiently. Nature has solved all these problems, not quite perfectly but far better than man can yet achieve, through the process of photosynthesis. Furthermore, by storing the energy in a stable chemical form, the plant is able to support far more than itself and so allow other forms of life to develop without having to capture their own energy. Man would hardly have evolved his unique capabilities if he had been compelled to remain a green body exposed most of the day to the sun!

Solar energy has created life and it maintains life very well today. It is undoubtedly within man’s capability to support a projected population of 10 billion with food grown by established agricultural methods. However, modern civilisation depends on a supply of energy far greater than that derived from food and this has come about because of our discovery of the wealth of fossil fuels. Although most of this dependence has grown up only over the last half century, it is now irreversible. Some economy might be possible but a very great reduction in energy supply would lead to untold suffering and death throughout the world. A solution must be found before the gas, oil and coal run out. Since coal supplies will be adequate for at least 200 years, there should be time to avert a crisis, and panic decisions are not only unnecessary but, in the present state of knowledge, they may actually delay progress to a satisfactory long-term solution.

The only long-term solutions seem to be nuclear fusion and solar energy and, since the sun is a nuclear fusion reactor, our choice is whether we shall have our reactor on the earth or 93 million miles away. In principle, either method would supply more than enough energy for man’s needs in the future; hydrogen is as plentiful as water and the solar energy falling on the desert regions of the earth, which are otherwise useless, is four thousand times greater than our present needs. But no net power has yet been drawn from a thermonuclear reactor and the cost of such a reactor cannot at present be even guessed. On the other hand, several kinds of solar energy collector are known which work reliably and reasonably efficiently but their cost at present, except for special uses, is prohibitive. Ultimately, the energy system adopted will be decided on economic grounds and a new discovery or idea in either field could transform the situation very quickly. The wise course to be taken at the present time is, therefore, a vigorous research programme covering a wide and exploratory field. In solar energy this need not be expensive since it is not necessary to experiment on a large scale. It is a great advantage of solar energy research that none of the methods is likely to be very dependent on size.

Energy is needed in three principal forms today… low grade heat (for buildings and water), electricity and chemical fuels. These are, of course, interconvertible to some extent but chemical fuels occupy a special place because they are the only form in which energy can be stored for longer than a few days and because the first energy shortage to appear will probably be that of the liquid hydrocarbon fuels necessary for our present means of transport. The conversion of solar energy into chemical potential is therefore of particular interest, and here one is led immediately to a consideration of the biological energy conversion process of photosynthesis. In the first place there is the possibility that more efficient and extensive forms of agriculture may enable us to grow our fuels, especially if coupled with a second stage of fermentation, so as to yield hydrogen or methane to replace natural gas and liquid hydrocarbons or alcohols to replace gasoline. These possibilities...

Produkt-Details

• Erscheint lt. Verlag: 24.9.2013
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Biologie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• ISBN-10: 1-4831-6378-4 / 1483163784
• ISBN-13: 978-1-4831-6378-9 / 9781483163789