27-06-2013, 03:50 PM
Cycling of Materials in Ecosystems
Cycling of Materials.pptx (Size: 548.85 KB / Downloads: 96)
Biogeochemical changes:
Humans throw away tons of garbage every year as unwanted, unneeded, and unusable. Nature, however, does not throw anything away.
Most energy flows through Earth’s ecosystems from the sun to producers to consumers.
The physical parts of the ecosystems, however, cycle constantly.
Carbon atoms are passed from one organism to another in a great circle of use.
Ecologists refer to such substances as cycling within an ecosystem between a living reservoir ( an organism that lives in the ecosystem) and a nonliving reservoir.
In almost all biogeochemical cycles, there is much less of the substance in the living reservoir than in the nonliving reservoir.
The Water Cycle:
Of all the nonliving components of an ecosystem, water has the greatest influence on the ecosystem’s inhabitants.
In the nonliving portion of the water cycle, water vapor in the atmosphere condenses and falls to Earth’s surface as precipitation as snow or rain.
Some of this water seeps into Earth’s surface (infiltration) and becomes part of groundwater, which is water retained beneath the surface of the Earth.
Most of the remaining water that falls to Earth does not stay on the surface.
Instead, heated by the sun, it reenters the atmosphere by evaporation.
In the living portion of the water cycle, much water is taken up by the roots of plants.
After passing through a plant, the water moves into the atmosphere by evaporating from the leaves, a process called transpiration.
Respiration:
Nearly all living organisms, including plants, engage in cellular respiration.
They use oxygen to oxidize organic molecules during cellular respiration, and carbon dioxide is a product of this reaction.
Combustion:
Carbon also returns to the atmosphere through combustion, or burning.
The carbon contained in wood may stay there for many years, returning to the atmosphere only when the wood is burned.
Sometimes carbon can be locked away beneath the Earth for millions of years, as in fossil fuels like oil, coal, and natural gas. The carbon in these is released when these fossil fuels are burned.