Cycles
The Water CycleBiological Importance: Water is essential to all organisms, and its availability affects the rates of ecosystem processes, especially primary production and decomposition in terrestrial ecosystems
Forms available to life: Liquid is the primary physical phase that water is used, however, some organisms can utilize water vapor Reservoirs: oceans contain 97%of the qater in the biosphere, 2% is contained in glaciers and polar ice caps, and rhe last 1% is in lakes, rivers, ground water and atmosphere Key Processes: the main process driving the water cycle are evaporation of liquid wayer by solar energy, condensation of the water vapor into clouds and precipitation. Transpiration by plants on land also moves large amounts of water into the atmosphere. Last, surface and ground water flow can return water to the oceans which completes the water cycle |
The Carbon CycleBiological Importance: carbon forms the framework of the organic molecules essential to all organisms
Forms available to life: photosynthetic organisms use carbon dioxide during photosynthesis and convert the carbon to organic forms that are used by consumers, such as animals, fungi, and heterotrophic protist and prokaryotes Reservoirs: major reservoirs are included in fossil fuels, soils, the sediments of aquatic ecosystems, the oceans, plant and animal biomass, and the atmosphere. The largest of these is the sedimentary rock such as linestone, however, this cycle occurs very slowly Key Processes: photosynthesis by plants and phtoplankton removes substsntial amounts of atmospheric CO2 every year, this amount is apporximately equaled by CO2 added to the atmosphere through cellular respiration by producers and consumers. The burning of fossil fuels and wood also adds a significant amount of additional CO2 into the atmosphere |
The Nitrogen CycleBiological Importance: Nitrogen is part of amino acids, proteins and nucleic acids and is often a limitinf plant nutrient
Forms available to life: plants can use 2 inorganic forms of nitrogen: ammonium and nitrate, and some organic forms such as amino acids. Some bacteria can use all these forms as well including nitrate, while animals can only use organic forms Reservoirs: Main reservoirs of nitrogen is in the atmosphere, which is 80% free nitrogen gas. Other reservoirs of inorganic and organic nitrogen compounds include soils and the sediments of lakes, rivers, and oceabs Key Processes: the major pathway for nitrogen to enter an ecosystem is through nitrogen fixation, the conversion of N2 to forms that can be used to synthesize organic nitrogen compounds. Certain bacteria, as well as lightning, fux nitrogen naturally. Nitrogen inputs from from human activities now ooutspace natural inputs on land. 2 major contributors are industrially produced fertilizers and legume crops that fix nitrogen through bacteria in their root nodules. Other bacteria in soul convert nitrogen to different forms |
The Phosphorus CycleBiological Importance: organisms require phosphorus as a major constituent of nucleic acids, phospholipids, and ATP and other energy-storing molecules and as a mineral factor of bones and teeth
Forms available to life: the most biologically important inorganic form of phosphorus is phosphate, which plants absorb and use in the synthesis of organic compounds Reservoirs: the largest accumulations of phosphorus are in sedimentary rocks of marine origin. There are also large quantities of phosphorus in soil, in the oceans, and in organisms. Because soil particles binds phosphate, the recycling of phosphorus trnds to he quite localized in ecosystems Key Processes: wethering of rocks gradually adds phosphate to soil, some leaks into the groundwater and surface water and may eventually reach the sea. Phosphate tsken up by producers and incorporated into biological milecules maybe be eaten by decomposition of biomass or |