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Lecture_11 - # :(p41213)aswellas Chapter20. (support)theord

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24 Nov 09 BioS 230 lecture # 11 on Ecosystem Energy Flow Reading for today’s lecture: Be sure to read the Introduction to Part 6 (p412-13) as well as  Chapter 20. Think about that Introduction in terms of ideas dealt with earlier in BioS 230. A regular input of energy is necessary to maintain (support) the order (functioning) of living  systems. The energy necessary to build macromolecules comes from the SUN. Energy arrives from the sun at a constant rate (per cross-sectional unit area of a sphere  centered on the sun) 24 hr per day, 365 days per year. Figure 2.3 describes the fate of solar  radiation. 30% is reflected back into space, 19% is absorbed by clouds and the atmosphere,  51% reaches the surface of the earth. Of the 51 units, 23 are involved in evaporation of water  and 7 contribute to currents in the atmosphere, less than 1% is used in photosynthesis, of the  20 units remaining it bounces back and forth between the atmosphere and the earth about 6  times.  BioS 230 Fall 2009 Page 1
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From Wikipedia solar spectrum Part of the visible solar energy is captured by plants (autotrophs) and used to build  macromolecules (with potential energy). This conversion of radiant energy to chemical bond  energy is called/measured as  productivity  by ecologists. The total energy captured is called  Gross primary productivity, but since the plants use some of that energy to keep themselves  functioning (respiration by autotrophs) the energy available to consumers is  net primary  productivity, NPP . Because of the tilt of the earth’s axis generating seasons NPP is always  expressed on a per year basis - the only fair way to compare places on different parts of the  earth. Measuring NPP over a whole year is difficult. Measuring the standing crop of biomass is  considerably easier. The SI unit of energy is the Joule, 1J = 1 kgm 2  sec -2  = 1 Watt sec = 0.239  calories.  At distance of earth from sun solar energy = 1.366 kW/m ² , which is equivalent to 1.96 calories  per minute per square centimeter. Not all that energy reaches the earth and not all is in visible 
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