Study Guide for Chapter 56

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Biological Sciences
Mary Olaveson

Chapter 56 Ecosystem & Global Economy Unlike energy, which is lost as it travels up the trophic levels; chemical compounds remain unchanged and can be reused, in processes which are often cyclic The movement of energy and materials on Earth is between 4 compartments: Oceans, Fresh Waters, Atmosphere, and Land Oceans At one point or another, most materials that cycle through the four compartments end up in oceans Despite their massive size, oceans only exchange materials with the atmosphere on the surface therefore they respond very slowly from input of other departments In most of the oceans, there is very slow mixture. Most material sink to the bottom and stay there for millions of years, however sometimes the material is brought back up to surface water, causing upwelling zones which support high rates of photosynthesis Freshwater Freshwater consists of rivers, lakes, and groundwater. Water travels very fast through them In lakes, minerals and nutrients are taken up by organisms which they incorporate into their cells. Once these organisms die, they take with them the nutrients and minerals. Often, deteritivores consume the oxygen by eating their tissues Therefore the surface waters of lakes quickly become depleted of nutrients while deeper waters become depleted of oxygen This is often resolved by a process known as turnover, which brings nutrients to the surface of lakes and oxygen to the bottom of the lakes Turnovers in shallow lakes are driven by winds whereas in deep lakes, it is driven by temperature In the case of deep lakes, turnovers occur because water is at its densest at 4, anything above or below that causes it to expand. Therefore in the winter, the coldest waters float to the surface and are usually covered by ice and the waters below remains at 4. When spring comes and ice melts, the surface also becomes 4. At this point all the water is uniform and the wind can mix the water, allowing nutrients to float to the top and oxygen to reach the bottom
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