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Life Under the Sun

Life Under the Sun

Peter A. Ensminger
Copyright Date: 2001
Published by: Yale University Press
Pages: 276
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  • Book Info
    Life Under the Sun
    Book Description:

    Which fungus is as sensitive to light as the human eye? What are the myths and facts about the ozone hole, tanning, skin cancer, and sunscreens? What is the effect of light on butterfly copulation? This entertaining collection of essays explores how various organisms-including archaebacteria, slime molds, fungi, plants, insects, and humans-sense and respond to sunlight.The essays in Peter A. Ensminger's book cover vision, photosynthesis, and phototropism, as well as such unusual topics as the reason why light causes beer to develop a "skunky" odor. He introduces us to the kinds of eyes that have evolved in different animals, including those in a species of shrimp that is ostensibly eyeless; gives us a better appreciation of color vision; explains how plowing fields at night may be used to control weeds; and tells about variegate porphyria, a metabolic disease that makes people very sensitive to sunlight and may have afflicted King George III of England.These engaging essays present a complicated yet fascinating subject in an accessible way. The book will be treasured by anyone interested in the wonders of biology.

    eISBN: 978-0-300-13352-3
    Subjects: General Science

Table of Contents

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  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
  3. Preface
    (pp. vii-x)
  4. Acknowledgments
    (pp. xi-xii)
  5. Introduction
    (pp. 1-10)

    The earth, which is 93 million miles from the sun, receives a small fraction of the light that the sun radiates into space, but that small fraction serves as the energy source that supports life on our planet. People have long appreciated the great significance of the sun. Many ancient cultures in Africa, Asia, and the Americas put it at the center of their religions. Many other cultures, both ancient and modern, have recognized that the sun provided them with the light and warmth that sustained them and their crops, and have used the sun as a cultural or religious...

  6. 1 Vision at the Threshold
    (pp. 11-19)

    Vision is surely the most important of our senses. A single glance instantly gives us information about our surroundings that is much more sophisticated than that from our other senses. Our eyes perform many amazing feats. They focus on objects at different distances, adapt to ambient light levels that vary more than a billionfold in brightness, and discriminate among many different colors, from the violet to the red.¹ One of the most remarkable features of our eyes is that they can function at extraordinarily low light levels.

    How much light do we need to see? Experiments performed under certain controlled...

  7. 2 The Five Percent Solution to Vision
    (pp. 20-30)

    So begins a famous passage entitled “Organs of Extreme Perfection and Complication” inThe Origin of Species.¹

    Half a century before Darwin, the theologian William Paley made an eloquent exposition of what has become known as the “argument from design” in his bookNatural Theology.² Paley argued that just as a watch is evidence of a watchmaker, the eye and other functionally complex organs are evidence of God, a supreme creator. The Scottish philosopher David Hume, however, criticized the argument from design a full century before Darwin by arguing that intricately designed organs cannot provide positive evidence for a supreme...

  8. 3 A More Delightful Vision
    (pp. 31-42)

    The colors we see depend on the wavelength sensitivities of the visual receptors within our eyes as well as the wavelengths of light that enter our eyes. In color vision light excites different classes of photoreceptor cells, containing different visual pigments, and the brain compares their differential light absorption.¹ Thus in bright light humans see a colorful world because the cone cells in our retinas have three visual pigments, with maximal sensitivities in the blue (~425 nm), green (~530 nm), and red (~560 nm) regions of the spectrum, and the differential responses of these cells enables color vision.² But our...

  9. 4 A Burning Issue
    (pp. 43-55)

    Fair-skinned people who have had sunburns are personally familiar with at least one of the harmful effects of ultraviolet radiation. But all the media play given to the ozone hole, tanning, skin cancer, sunscreens, and related topics has created a lot of confusion and misunderstanding. Is the ozone layer really thinning, or is this just a hoax propagated by environmentalists? Is tanning under artificial sunlamps safer than tanning outdoors? What are the chances of developing skin cancer? Can sunscreens really protect against sunburns and skin cancer?

    The chemically heterogeneous ozone layer contains about 90 percent of the atmosphere’s ozone (O3)...

  10. 5 A SAD Tale
    (pp. 56-68)

    Physicians have long known that the moods of certain people change with the seasons. More than two thousand years ago, Hippocrates, the father of medicine, reportedly said, “Of constitutions, some are well or ill adapted to summer, others are well or ill adapted to winter.” Poets and novelists have also noted these seasonal changes in mood. Emily Dickinson, battered by a moody disposition herself, wrote

    There’s a certain Slant of light,

    Winter Afternoons—

    That oppresses, like the Heft

    Of Cathedral Tunes—

    Victor Hugo, while in exile on the Channel Islands, wrote inLes Miserables,“Winter changes into stone the water...

  11. 6 The Purple Disease
    (pp. 69-79)

    As a resident of upstate New York, where winter days are as short as eight hours and winter snowfall can be up to two hundred inches, I definitely become more upbeat with the arrival of the warm and sunny weather of spring. People with seasonal affective disorder undergo more dramatic changes in mood with seasonal changes in day length. They experience deep depression during the winter and dramatic relief during the spring (see Chapter 5). Of course, nobody—not even people with seasonal affective disorder—should stay out in the sun for prolonged periods, because the sun’s ultraviolet rays can...

  12. 7 A Novel Method of Weed Control
    (pp. 80-94)

    The sun’s radiation is the most important energy source for life on earth. Chlorophyll, the best known plant pigment, uses the sun’s energy to drive photosynthesis, the conversion of solar energy into biochemical energy. Nearly all other organisms depend upon plants as food, either directly or indirectly, so they also depend upon photosynthesis. Photosynthesis is the best known example of biological energy transduction, the transformation of light energy into chemical energy.

    Plants, animals, and bacteria also have photosensory pigments that are important in sensory transduction, not because they harness energy from the sun but because they allow organisms to sense...

  13. 8 Light and Beer
    (pp. 95-103)

    Have you ever cleaned and dried your favorite beer glass, chilled your favorite brew, popped the cap and filled your glass, only to be put off by a “skunky” odor?

    If so, your beer was probably destroyed by light in the wellknown sunstruck reaction (see figure A7, Appendix, and sidebar, “A Windowsill Experiment”). In this reaction, ultraviolet or blue light chemically transforms certain hop compounds in beer and gives the beer an unpleasant odor.¹ This is why brewers must always keep their beer away from light. Some commercial brewers use an alternative approach to protect their beer. They brew with...

  14. 9 Phycomyces, the Fungus That Sees
    (pp. 104-115)

    Most of us would consider vision the most important of our five senses, for it provides us with so much important information about the world. In fact, our eyes seem remarkably well adapted, in an evolutionary sense, to the light environment of the earth. The sunlight that reaches the earth is mostly between 400 nm (violet) and 700 nm (deep red) and our visual system is maximally sensitive to radiation in this part of the spectrum.¹ Our eyes are so sensitive to light that a single rhodopsin-containing rod cell of the retina can respond to the absorption of a single...

  15. 10 Dictyostelium, the Amoeba and the Slug
    (pp. 116-127)

    In 1869, just as Mad King Ludwig began building his fantasy castles in Bavaria, a more down-to-earth German, a biologist named Oskar Brefeld, described his discovery of an unusual organism that he found growing on horse excrement.¹ Brefeld did not realize the significance of this new organism until he examined its unusual life cycle in the laboratory, growing it on a medium of cooked horse dung. This new organism, which Brefeld namedDictyostelium mucoroides,was the first species to be identified in an entire taxonomic class now called the Dictyostelia—the cellular slime molds. The cellular slime molds are so...

  16. 11 High Hopes for Hypericin
    (pp. 128-138)

    Saint John’s wort has been in the news quite a lot in recent years. In the late 1980s, several studies showed that red pigments derived from this herb—hypericin and pseudohypericin—inactivated or blocked the reproduction of certain retroviruses in mice. This led to speculation that these compounds might be effective against human retroviruses, including the human immunodeficiency virus (HIV), the virus associated with AIDS.¹ Indeed, subsequent preclinical studies showed that hypericin could destroy the equine infectious anemia virus and the related human immunodeficiency virus.² By the start of 2000, no clinical studies had demonstrated that hypericin or Saint John’s...

  17. 12 Turning on a Butterfly
    (pp. 139-148)

    We are all used to thinking that animals see with their eyes, but some animals have photoreceptors in rather unusual and unexpected places.¹ The sea star, though without a head or a brain, has photoreceptive eyespots near the end of its arms.² Birds and lizards, whose thin skulls let in light, have photoreceptor cells in the pineal glands of their brains, cells that resemble the highly specialized cone cells found in the retinas of vertebrates’ eyes.³ Many roundworms have specialized light-sensitive epidermal cells, as well as eyes with lenses and retinas.⁴ But the animal with photoreceptors in the most unusual...

  18. 13 Blue Moons and Red Tides
    (pp. 149-160)

    In September 1883 many residents of the tropics were amazed when they looked skyward. The sun and moon were blue! These heavenly bodies returned to their original yellow-white color by October, but people the world over noted that their sunsets were particularly red and beautiful for the next year or so.¹

    In September of the following year, residents along the gulf coast of Florida were shocked when they looked out to sea. During the day, they saw that their ocean had turned red and that thousands of dead fish had washed ashore.²

    Blue moons and red tides! What could cause...

  19. 14 Photosynthesis and the Great Salt Lake
    (pp. 161-172)

    Observers of nature once classified all organisms as plants or animals. Beginning in the seventeenth century important discoveries by the Dutch biologist Antoni van Leeuwenhoek revealed that there was more to life. Between 1673 and 1723 Leeuwenhoek built microscopes from lenses that he painstakingly ground himself, and with these instruments he discovered animacules (little animals) — bacteria and other single-celled organisms. Leeuwenhoek submitted a series of letters to the Royal Society of London that described his important discoveries.¹ Many years later, biologists discovered that certain single-celled organisms lacked nuclei, the DNA-bearing structures found in the cells of all higher organisms. This...

  20. 15 Too Much of a Good Thing
    (pp. 173-182)

    Just as the wolves eat the moose and the moose eat the plants, each class of organisms in a food chain consumes the food energy of a different class of organisms. All food chains require primary producers—organisms that provide an energy input. Although there are many different types of food chains on earth, there are only a few basic mechanisms for putting energy into food chains. One of the most unusual of these is used by bacteria that live near hydrothermal vents that lie a mile or more beneath the ocean surface. They use energy from the oxidation of...

  21. Appendix: A Menagerie of Molecules
    (pp. 183-200)
  22. Notes
    (pp. 201-258)
  23. Glossary
    (pp. 259-268)
  24. Index
    (pp. 269-276)