<P> Food webs depict energy flow via trophic linkages . Energy flow is directional, which contrasts against the cyclic flows of material through the food web systems . Energy flow "typically includes production, consumption, assimilation, non-assimilation losses (feces), and respiration (maintenance costs)." In a very general sense, energy flow (E) can be defined as the sum of metabolic production (P) and respiration (R), such that E = P + R . </P> <P> Biomass represents stored energy . However, concentration and quality of nutrients and energy is variable . Many plant fibers, for example, are indigestible to many herbivores leaving grazer community food webs more nutrient limited than detrital food webs where bacteria are able to access and release the nutrient and energy stores . "Organisms usually extract energy in the form of carbohydrates, lipids, and proteins . These polymers have a dual role as supplies of energy as well as building blocks; the part that functions as energy supply results in the production of nutrients (and carbon dioxide, water, and heat). Excretion of nutrients is, therefore, basic to metabolism ." The units in energy flow webs are typically a measure mass or energy per m per unit time . Different consumers are going to have different metabolic assimilation efficiencies in their diets . Each trophic level transforms energy into biomass . Energy flow diagrams illustrate the rates and efficiency of transfer from one trophic level into another and up through the hierarchy . </P> <P> It is the case that the biomass of each trophic level decreases from the base of the chain to the top . This is because energy is lost to the environment with each transfer as entropy increases . About eighty to ninety percent of the energy is expended for the organism's life processes or is lost as heat or waste . Only about ten to twenty percent of the organism's energy is generally passed to the next organism . The amount can be less than one percent in animals consuming less digestible plants, and it can be as high as forty percent in zooplankton consuming phytoplankton . Graphic representations of the biomass or productivity at each tropic level are called ecological pyramids or trophic pyramids . The transfer of energy from primary producers to top consumers can also be characterized by energy flow diagrams . </P> <P> A common metric used to quantify food web trophic structure is food chain length . Food chain length is another way of describing food webs as a measure of the number of species encountered as energy or nutrients move from the plants to top predators . There are different ways of calculating food chain length depending on what parameters of the food web dynamic are being considered: connectance, energy, or interaction . In its simplest form, the length of a chain is the number of links between a trophic consumer and the base of the web . The mean chain length of an entire web is the arithmetic average of the lengths of all chains in a food web . </P>

Who gets the least amount of energy in a food web
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