Notes on Biogeochemical Cycles and Ecology.pdf

nutrients from the inorganic nutrient pool, which is usually the soil or watersurrounding the plants or algae. These inorganic nutrients are passed from organism toorganism as one organism is consumed by another. Ultimately, all organisms die andbecome detritus, food for the decomposers. At this stage, the last of the energy isextracted (and lost as heat) and the inorganic nutrients are returned to the soil or waterto be taken up again. The inorganic nutrients are recycled, the energy is not.Many of us, when we hear the word "nutrient" immediately think of calories and thecarbon-carbon bonds that hold the caloric energy. IT IS VERY IMPORTANT thatyou be careful in your use of the word nutrient in this sense. When writing aboutenergy flow and inorganic nutrient flow in an ecosystem, you must be clear as to whatyou are referring. Unmodified by "inorganic" or "organic", the word "nutrient" canleave your reader unsure of what you mean. This is one case in which the scientificmeaning of a word is very dependent on its context. Another example would be theword "respiration", which to the layperson usually refers to "breathing", but whichmeans "the extraction of energy from carbon-carbon bonds at the cellular level" tomost scientists (except those scientists studying breathing, who use respiration in thelay sense).To summarize: In the flow of energy and inorganic nutrients through the ecosystem, afew generalizations can be made:1. The ultimate source of energy (for most ecosystems) is the sun2. The ultimate fate of energy in ecosystems is for it to be lost as heat.3. Energy and nutrients are passed from organism to organism through the foodchain as one organism eats another.4. Decomposers remove the last energy from the remains of organisms.5. Inorganic nutrients are cycled, energy is not.Food Chains and Webs:A food chain is the path of food from a given final consumer back to a producer. Forinstance, a typical food chain in a field ecosystem might be:grass ---> grasshopper --> mouse ---> snake ---> hawkNote that even though I said the food chain is the path of food from a given finalconsumer back to a producer we typically list a food chain from producer on the left(or at the bottom) to final consumer on the right (or at the top). Note to internationalreaders: In Hebrew or Aramaic, or other languages which are read right-to-left, is itcustomary to list the food chains in the reverse order? By the way, you should be ableto look at the food chain above and identify the autotrophs and heterotrophs, and