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E5. More energy flows through a community than is captured in living mass.


Student Outcome: E5.1

Illustrate how some of the energy that enters the community is captured as chemical bonds, and most is lost as heat.


Almost all life on earth is ultimately maintained by transformations of energy from the sun. Plants capture the sun's energy and use it to synthesize complex, energy-rich molecules (chiefly sugars) from molecules of carbon dioxide and water. These synthesized molecules then serve, directly or indirectly, as the source of energy for the plants themselves and ultimately for all animals and decomposer organisms (such as bacteria and fungi). This is the food web: The organisms that consume the plants derive energy and materials from breaking down the plant molecules, use them to synthesize their own structures, and then are themselves consumed by other organisms. At each stage in the food web, some energy is stored in newly synthesized structures and some is dissipated into the environment as heat produced by the energy-releasing chemical processes in cells. A similar energy cycle begins in the oceans with the capture of the sun's energy by tiny, plant-like organisms. Each successive stage in a food web captures only a small fraction of the energy content of organisms it feeds on.




Source: http://www.project2061.org/publications/sfaa/online/chap5.htm


Nice simulation of the flow of energy - go here


Student Outcome: E5.2

Know that the level of energy available may limit the productivity in a community.


The ultimate source of energy for life on Earth is the sun. Solar energy is trapped during the process of photosynthesis and converted into a chemical form that we normally call food. Food contains both materials (the elements carbon, hydrogen, nitrogen, and the other essential elements) as well as stored energy. The materials within the food are recycled. They pass from the producers to the consumers and finally are recycled back to the producers by the action of the decomposers. Energy, unlike the materials, is not recycled. As the food is passed through the food web, energy is lost. In general terms, only 10% of the energy stored in one trophic level (such as producers) is actually transferred t the next trophic level (for example the herbivores). This is known as the pyramid of energy. Eventually there is so liitle energy remaining in the top trophic level that no highr trophic level can be supported. This is why there are few if any fourth order consumers in any ecosystem.


Source: http://www.chs.k12.nf.ca/science/b3201/WebCT-Copy/units/unit1-05.htm


Each trophic level in a food web consumes the lower trophic level in order to obtain energy. But not all of the energy from one trophic level is transferred to the next. At each trophic level, most of the energy is used up in running body processes such as respiration. Typically, just 10 percent of the energy present in one trophic level is passed along to the next. If the energy present in the producer trophic level of a food web is kcal, you could draw an energy pyramid to show the transfer of energy from one trophic level to the next:

The energy lost between each trophic level affects the number of organisms that can occupy each trophic level. If the secondary consumer trophic level contains 10 percent of the energy present in the primary consumer level, it follows that there can only be about 10 percent as many secondary consumers as there are primary consumers. The energy pyramid is therefore also a biomass pyramid that shows the number of individuals in each trophic level.


Source: http://www.sparknotes.com/testprep/books/sat2/biology/chapter10section3.rhtml


Here is a rather dry simulation but it is a good introduction to this very difficult concept.  Persist!


Student Outcome: E5.3

Know that the input and the output of energy on the Earth are almost equal.



Source: http://geography.berkeley.edu/ProgramCourses/CoursePagesFA2006/Geog40/L5.pdf#search=%22Earth%20energy%20input%20output%22


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