Glimpses of Creatures in Their Physical Worlds - Softcover

Vogel, Steven

Softcover

ISBN 10: 0691138079 ISBN 13: 9780691138077

Verlag: Princeton University Press, 2009

Inhaltsangabe

Glimpses of Creatures in Their Physical Worlds offers an eye-opening look into how the characteristics of the physical world drive the designs of animals and plants. These characteristics impose limits but also create remarkable and subtle opportunities for the functional biology of organisms. In particular, Steven Vogel examines the size and scale, and trade-offs among different physical processes. He pays attention to how the forms and activities of animals and plants reflect the materials available to nature, and he explores the unique constraints and possibilities provided by fluid flow, structural design, and environmental forces.

Each chapter of the book investigates a facet of the physical world, including the drag on small projectiles; the importance of diffusion and convection; the size-dependence of acceleration; the storage, conduction, and dissipation of heat; the relationship among pressure, flow, and choice in biological pumps; and how elongate structures tune their relative twistiness and bendiness. Vogel considers design-determining factors all too commonly ignored, and builds a bridge between the world described by physics books and the reality experienced by all creatures. Glimpses of Creatures in Their Physical Worlds contains a wealth of accessible information related to functional biology, and requires little more than a basic background in secondary-school science and mathematics.

Drawing examples from creatures of land, air, and water, the book demonstrates the many uses of biological diversity and how physical forces impact biological organisms.

Über diesen Titel

Über die Autorin bzw. den Autor

Steven Vogel (1940–2015) was the James B. Duke Professor Emeritus of Biology at Duke University. His many books include Comparative Biomechanics (Princeton) and Cats' Paws and Catapults.

Von der hinteren Coverseite

"This charismatic book is a fascinating read and Vogel is exceptionally good at presenting the material so that it is accessible to a general audience. The book presents new conceptions, data, and interpretations, but its most impressive aspect is the wide range of diverse examples collected in one place, displaying a lifetime's worth of accumulated knowledge and wisdom."--Amy S. Johnson, Bowdoin College

"The book draws case studies from an enormous diversity of organisms, and the scholarship is meticulous--the sources used and cited are both appropriate and extensive. They not only contribute to the text itself, but also comprise a bibliography that will be widely consulted by students at many levels and by readers interested in pursuing specific topics in more depth."--Sharon Swartz, Brown University

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Glimpses of Creatures in Their Physical Worlds

By Steven Vogel

PRINCETON UNIVERSITY PRESS

Copyright © 2009 Princeton University Press
All right reserved.
ISBN: 978-0-691-13807-7

Contents

Preface.................................................................viiChapter One Two Ways to Move Material..................................1Chapter Two The Bioballistics of Small Projectiles.....................18Chapter Three Getting Up to Speed......................................39Chapter Four Moving Heat Around........................................58Chapter Five Maintaining Temperature...................................80Chapter Six Gravity and Life in the Air................................95Chapter Seven Gravity and Life on the Ground...........................116Chapter Eight Gravity and Life in Water................................141Chapter Nine Making and Maintaining Liquid Water.......................164Chapter Ten Pumping Fluids through Conduits............................184Chapter Eleven To Twist or Bend When Stressed..........................209Chapter Twelve Keeping Up Upward and Down Downward.....................232List of Symbols.........................................................259References and Index of Citations.......................................263Index...................................................................289

Chapter One

Two Ways to Move Material

Introducing a Variable

"No man is an island, entire of itself," said the English poet John Donne. Nor is any other organism, cell, tissue, or organ. We're open systems, continuously exchanging material with our surroundings as our parts do with their surroundings. In all of these exchanges, one physical process inevitably participates. In that process, diffusion, thermal agitation, and place-to-place concentration differences combine to produce net movements of molecules. On almost any biologically relevant scale, it can be described by exceedingly precise statistical statements, formulas that take advantage of the enormous numbers of individual entities moving around. Since it incurs no metabolic expenditure, it's at once dependable and free.

But except over microscopic distances, diffusion proceeds at a glacial pace. For most relevant geometries, doubling distance drops the rate of transport per unit time by a factor, not of two, but of four. Diffusive transport that would take a millisecond to cover a micrometer would require no less than a thousand seconds (17 minutes) to cover a millimeter and all of a billion (a thousand million seconds or 3 years) for a meter. Diffusion coefficient, the analog of conventional speed, has dimensions of length squared per time rather than length per time—it's not a rate in the ordinary sense.

Some organisms rely exclusively on diffusion to move material internally and to transfer it to and from their surroundings. Unsurprisingly, they're either very small or very thin or (as in many coelenterates and macroalgae) bulked up with metabolically inert cores. Diffusion coefficients in air run about 10,000 times higher than in water, which translates into a hundred-fold (the square root of 10,000) distance advantage. So under equivalent circumstances, those living in air or transferring gases (as do many arthropods) can get somewhat larger—perhaps one hundred-fold—but then still face that daunting size-dependence of diffusion. In response, one might say, macroscopic organisms inevitably augment diffusion with an additional physical agency, variously termed convection, advection, or just bulk flow, in any case fluid flow en masse. Circulatory systems as conventionally recognized represent only one version of this ubiquitous fix.

Indeed, the size scale at which life switches from reliance solely on diffusive exchange to convection supplementation—very roughly 10 micrometers—corresponds, roughly, to the switch from cellular to multicellular organization. While being essentially one- or two-dimensional does permit macroscopic size, it comes with obvious limitations. And while many plant cells, about which more shortly, do get comparatively large, they quietly practice intracellular bulk flow.

Solari et al. (2006) explore this transition point, using as material flagellated colonial green algae, mainly Volvox. In this genus, active cells populate the periphery of spherical colonies around 0.5 millimeters in diameter. The daughter colonies within (as in plate 1.1) depend on coordinated beating of the parental flagella on the outside of the colony to create enough external flow for adequate exchange of metabolites and wastes. Even at this relatively small size, flow plays an important role—in effect they have circulatory systems located around their external surfaces. Deflagellating colonies lowers photosynthetic productivity; providing forced external fluid motion (a bubbler in the suspension) restores normality.

One might expect good design to balance the two physical processes. Excessive reliance on diffusion would limit size, slow the pace of life, or require excessively surface-rich geometries. Excessive reliance on flow would impose an unnecessary cost of pumping (chapter 10) or require an unnecessarily large fraction of body volume for pipes, pumps, and fluid. So for biological systems a default ratio of convective transport to diffusive transport should be around one. As it happens, the chemical engineers provide us with just such a ratio. This so-called Péclet number, Pe, is a straightforward dimensionless expression:

Pe = vl/D, (1.1)

where v is flow speed, l is transport distance, and D is the diffusion coefficient. (Confusingly, a heat-transfer version of the Péclet number may be more common than this mass-transport form; it puts thermal diffusivity rather than the molecular diffusion coefficient in its denominator.)

Calculating values of the Péclet number can give us more than merely a way to check up on the performance of the evolutionary process. Often it can test hypotheses about the primary function of various features of organisms—"primary" in the sense of being most constraining on design. Perhaps that justification can be best put as a series of examples, which will follow after a few words about the origin of the ratio.

One can view the Péclet number several ways. The simplest sees it as the ratio of a convective or flow rate, v, to a diffusion rate, D/l. A slightly more formal version combines a simple numerator, mv, for flowing momentum, with a denominator that represents a simplified form of Fick's first law for diffusive momentum transport, DSm/V, where S is cross-sectional area and V is volume. Taking l² as a crude proxy for area and l³ for volume, one gets equation (1.1).

From a slightly different viewpoint, the Péclet number represents the product of the Reynolds number (Re) and the Schmidt number (Sc). The first,

Re = ρlv/μ, (1.2)

where ρ and μ are fluid density and viscosity respectively, gives the ratio of inertial to viscous forces in a flow. At high values, bits of fluid retain a lot of individuality, milling turbulently as in a disorderly crowd; at low values, bits of fluid have common aspirations and tend to march in lockstep formation. In short, Reynolds number characterizes the flow. The Schmidt number,

Sc = μ/ρD, (1.3)

is the ratio of the fluid's kinematic viscosity (viscosity over...

Details zur Ausgabe

• Verlag: Princeton University Press
• Erscheinungsdatum: 2009
• Sprache: Englisch
• ISBN 10: 0691138079
• ISBN 13: 9780691138077
• Einband: Taschenbuch
• Anzahl der Seiten: 302
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Buchbär; info@buchbaer.de; ; Weberstr. 67; Osnabrück; 49084; Deutschland