The Role of Theory in Advancing 21st-Century Biology Catalyzing Transformative Research (2008) / Chapter Skim
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4 What Role Does Life Play in the Metabolism of Planet Earth?
4 What Role Does Life Play in the Metabolism of Planet Earth?
Pages 67-80
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From page 67... ...
The biological conversion of solar energy into chemical energy ultimately became the primary source of energy for all life on the Earth's surface. Through an obscure series of evolutionary occurrences, the highest energy state that evolved produced oxygen as a byproduct of splitting water; the hydrogen atoms were used to form organic matter from carbon dioxide.
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From page 68... ...
An important challenge at the intersection of biology, geochemistry, and physics is to understand how the global metabolic network evolved, what the feedbacks were that led to the constrained variations in gas composition of the planetary atmosphere, and the limitations of these processes on organismal, ecological, and geological spatial and time scales. Understanding this vast global metabolic network requires developing a global "systems geobiology," the root of which lies in the origins of life on Earth and which is deeply grounded in the fundamental physiological pathways of life.
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From page 69... ...
reduce the generation of noxious metabolic byproducts and accelerate their safe disposal. The issues addressed by systems geobiology are fundamental in public discourse; these issues include understanding the importance of metabolism for all life on Earth and the extent to which specific metabolic processes can be altered to ameliorate human-caused effects on biogeochemical cycles.
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From page 70... ...
Although biologists do not have a detailed understanding of how these energy transfer machines evolved on a subcellular level, these shared molecular entities now form an interdependent planetary "electron market" where reductants and oxidants are exchanged across the globe. The scale of this electron market is planetary because gases, produced by all organisms, can be transported around Earth's surface by the ocean and the atmosphere.
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From page 71... ...
The formation of reduced products from sunlight, organic molecules, or inorganic reduced molecules. Energy is transferred to reduced hydrogen or electron carriers that are then used directly for anabolic reactions (3)
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From page 72... ...
METABOLISM: A CELLULAR PROCESS WITH GLOBAL CONSEQUENCES The study of metabolic processes, in all their guises, is a unifying theme in biology. Studying metabolism, the flow of energy and molecules in the cell, at almost any level of organization is a challenging enterprise that demands the development of imaginative conceptual approaches and new technologies (Box 4-1)
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From page 73... ...
Interpreting the stable isotope signals of life's metabolism requires putting together information derived from the study of metabolic processes at levels that range from cells to broad geographical regions. All the macromolecules that comprise life are composed of six major ele ments: H, C, N, O, S, and P
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From page 74... ...
For example, large-scale heat production is critical for complex behavior in metazoans and is the base for endothermy in mammals and birds. Large-scale heat production also occurs in microbial communities, in termite and ant colonies, and at ecosystem levels, when forests and phytoplankton dissipate large fractions of absorbed solar energy, thereby altering the thermal structure of the local environment (Lewis et al., 1990; Gates, 2003)
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From page 75... ...
Indeed, without the burial of organic matter -- a geologically controlled process -- Earth would have remained anaerobic. The slow rise of oxygen through the mid to late Proterozoic altered forever the metabolic networks that subsequently evolved in the first half of Earth's history.
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From page 76... ...
. A recent flurry of theoretical explorations attempts to explain not only the seeming universal dependence of aerobic respiration on body mass and temperature but also the putative ubiquity of the value of ¾ in the exponent of the power function that relates metabolic rate with body size.
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From page 77... ...
In fact, our theoretical understand ing of metabolism now must incorporate the realization that all organisms -- from plants to invertebrates to mammals -- have an associated microbial community that affects many aspects of their physiology, including metabolism. The analysis of the metagenomes of various host-associated microbial communities has been used to diagnose functional metabolic differences among communities (Tringe et al., 2005)
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From page 78... ...
Although the theory undoubtedly has limitations, it is a bold and promising attempt. The ubiquity of the power functions relating metabolic function to body size and the importance of temperature for biological processes are undeniable.
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From page 79... ...
Thus, a deep understanding of these fluxes will require input from fields as diverse as enzymology, protein chemistry, cell biology, biophysics, comparative physiology, and ecology, just to list some of the necessary biologists' areas of expertise. Understanding the biosphere's metabolism will require that technologies developed to measure metabolic processes at small scales be refined and scaled up to appropriately broad temporal and spatial scales.
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From page 80... ...
Over the next century, a major challenge for society will be to develop or redesign metabolic pathways, based primarily on microbial systems, to greatly accelerate fluxes of materials and energy. One of the major outcomes of understanding metabolic pathways and energy transformation processes is to replace technologies designed in the 19th and 20th centuries with sustainable processes that are biologically driven.
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