Cycling of Materials in Ecosystems -by Kiera Davis, Period 6
-Water, carbon, nitrogen, and phosphorus all take paths from the nonliving environment to living organisms, such as trees, and then back to the nonliving environment. These paths form cycles, known as biogeochemical cycles. In these cycles, a pathway is formed when a substance enters living organisms, stays for a long time, then returns to the nonliving environment. Such substances are referred to as cycling within an ecosystem between an organism that lives in the ecosystem and a nonliving reservoir.
The Water Cycle:
-Water has the greatest influence on the ecosystem’s inhabitants. Water vapor in the atmosphere, in the nonliving portion of the water cycle, condenses and falls to the Earth’s surface as rain, sleet, or snow. The water that seeps into the soil becomes part of the ground water, which is retained beneath the Earth’s surface. Most of the water the falls to Earth reenters the atmosphere by evaporation. In the living portion of the water cycle, a large majority of the water is taken up by plant roots. After it passes through the plant, the water moves into the the atmosphere by evaporating from the leaves, in a process called transpiration. This is a sun-driven process Earth’s atmosphere is heated by the sun, which creates wind currents that draw moisture from the small openings in the leaves of plants.
The Carbon Cycle:
-Carbon cycles between the nonliving environment and living organisms, as well. Carbon dioxide in the air or dissolved in water is used by photosynthesizing plants, algae, and bacteria as a raw material to build organic molecules. Carbon atoms may return to the pool of Carbon dioxide in the are and water in three ways…
1. Respiration– Nearly all living organisms engage in cellular respiration. They use oxygen to oxidize organic molecules during cellular respiration, and carbon dioxide is a byproduct of this reaction.
2. Combustion– The carbon contained in wood may stay there for years, returning to the atmosphere only when the wood is burned. Carbon can sometimes be locked away under the Earth for thousands or even millions of years. The remains of the organisms buried in sediments may be gradually changed by heat and pressure into fossil fuels like coal, oil, and natural gas. The carbon is released when the fossil fuels are burned.
3.Erosion– Marine organisms use CO2 dissolved in sea water to make calcium carbonate shells. Over millions of years, the shells from the sediments, which form limestone. As the limestone erodes and becomes exposed, the carbon becomes available to other organisms.
The Phosphorus and Nitrogen Cycles:
– Nitrogen and phosphorus are needed by organisms to build proteins and nucleic acids. Phosphorus is usually present in soil and rock as calcium phosphate, which dissolves `in water to form phosphate ions. This phosphate is absorbed by the roots of plants and used to build organic molecules. Animals that eat the plants reuse the organic phosphate. The process of combining nitrogen with hydrogen to form ammonia is called nitrogen fixation.