Energy Flow and the Water Cycle: Summary

<h1>Text Preview</h1> <p>In this activity, we've looked at how energy flows through an ecosystem. Light energy is constantly supplied by the sun, and converted to chemical energy by primary producers, the autotrophs. Primary producers are food for primary consumers, mainly the herbivores. Primary consumers are eaten by secondary consumers, which are carnivores. Secondary consumers are eaten by tertiary consumers, and so on. Omnivores feed on primary producers and at least one level of consumer. Detritivores, or decomposers, feed on nonliving organic material and are the link between all trophic levels. The feeding relationships in an ecosystem can be shown using a food chain or a more elaborate food web. </p> <p>It is rare to have trophic levels higher than quaternary consumers because energy is lost between each trophic level. Primary producers convert light energy to chemical energy through photosynthesis. Net primary productivity is an indication of how efficient the primary producers of an ecosystem are at converting the energy. Primary productivity can be expressed as biomass, the mass of dry vegetation produced in a given amount of time. Biomass is a rate, and shouldn't be confused with standing crop biomass, which is the dry mass of a crop at a particular time. Different ecosystems have different primary productivities, and they contribute different amounts to Earth's total primary productivity.</p> <p>Secondary productivity is the rate at which consumers convert the chemical energy from food into new body mass. Energy is lost between each trophic level. Only the energy stored as body mass in one trophic level is available for the next level. Generally the ecological efficiency of each level is around 5 to 20%, so 80 to 95% of the energy is lost at each level.</p> <p>The loss of energy can be diagrammed in several ways. A pyramid of productivity, a biomass pyramid, and a pyramid of numbers all show how energy is lost. Each pyramid is very bottom heavy, because the amount of energy converted by primary producers is much greater than the energy that is passed to higher- level consumers.</p> <p>While energy must be continuously supplied by the sun, water is recycled. The water cycle is the movement of water from the oceans, to land, and back to the oceans. As it moves, the water transfers nutrients within and between ecosystems.</p> <p>Now that we understand the movement of energy and water, let's use this knowledge to explore the presence of the insecticide DDT. DDT was originally used on plants and soil, but now it can be found everywhere. This is because of feeding relationships and the water cycle. DDT is picked up from the soil by primary producers. It is then passed to primary consumers, then to secondary consumers, and so on. DDT used in one ecosystem is transferred to other ecosystems through the water cycle. The spread of DDT is one example of why it's so important to keep all ecosystems free of hazardous materials. We can all do our part, by disposing of toxic materials properly, and keeping our water supplies from contamination by pollution and waste.</p> <p id="TextCopyright">Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education</p>