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This chapter explains the carbon, nitrogen, and phosphorus cycles in ecosystems, including the stages, human impacts, and environmental consequences. Learn how these essential elements are cycled between living and nonliving components of the environment.
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ENVIRONMENTAL SCIENCE Chapter 5 How Ecosystems Work 5.2 The Cycling of Materials
5.2 The Cycling of MaterialsObjectives • List the three stages of the carbon cycle. • Describe where fossil fuels are located. • Identify one way that humans are affecting the carbon cycle. • List the three stages of the nitrogen cycle. • Describe the role that nitrogen-fixing bacteria play in the nitrogen cycle. • Explain how the excess use of fertilizer can affect the nitrogen and phosphorus cycles.
The Carbon Cycle • The carbon cycle is the movement of carbon from the nonliving environment into living things and back. • Carbon is an essential component in the four major molecule types that make up living things – carbohydrates, lipids, proteins, and nucleic acids. • Carbon is cycled between land, air, atmosphere, and living things. • Carbon may enter into a short-term cycle or a long-term cycle. • A “sink” is a reservoir where something may be stored for some time.
The Carbon Cycle • Producers convert atmospheric carbon dioxide into carbohydrates during photosynthesis. • Consumers contain carbon from the carbohydrates in the producers they eat. • During cellular respiration, some of the carbon is released back into the atmosphere as carbon dioxide. • Some carbon is stored in limestone – one of the largest carbon sinks on Earth.
The Carbon Cycle • Carbon may also be released into the soil as organisms die and decompose. • The carbon and hydrogen from the remains of buried organisms can form coal, oil, or natural gas – fossil fuels. • Fossil fuels store the hydrocarbons left over from the remains of organisms that died millions of years ago.
The Carbon Cycle • When we burn fossil fuels, carbon is released back into the atmosphere – mostly as carbon dioxide. • In 2000, one third of all the carbon dioxide emitted in the U.S. came from motor vehicles. • When the carbon emitted from the burning of fossil fuels is added to the carbon emitted from other sources, the amount of atmospheric carbon increases. • Carbon dioxide is a greenhouse gas and may contribute to global warming – an overall increase in average temperatures around the world.
The Nitrogen Cycle • The nitrogen cycle is the process in which nitrogen circulates among the air, soil, water, and organisms in an ecosystem. • All organisms need nitrogen for building proteins – the building blocks of cells. • Nitrogen makes up 78% of gases in the atmosphere. • Nitrogen must be “fixed” before it can be used by organisms.
The Nitrogen Cycle • Only a few species of bacteria – nitrogen-fixing bacteria – can convert atmospheric nitrogen (N2) into a more useable form (such as ammonia – NH3). • Nitrogen-fixing bacteria live within the roots of legumes such as beans, peas, and clover. • The bacteria use sugar provided by the legumes to produce nitrogen containing compounds like nitrates (NO3-). • Excess nitrogen fixed by the bacteria is released into the soil.
The Nitrogen Cycle • Nitrogen stored within organisms is returned to the nitrogen cycle as decomposition occurs. • After decomposers return nitrogen to the soil, bacteria transform a small amount of the nitrogen into nitrogen gas, which then returns to the atmosphere.
http://www.waikato.ac.nz/wfass/subjects/geography/people/max/ConceptDiagrams.shtmlhttp://www.waikato.ac.nz/wfass/subjects/geography/people/max/ConceptDiagrams.shtml
The Phosphorus Cycle • The phosphorus cycle is the movement of phosphorus in different chemical forms from the environment to organisms and then back to the environment. • Phosphorus is an essential component of nucleic acids as well as many other important molecules to organisms. • Plants get phosphorus from the soil and water. • Animals get their phosphorus by eating plants or animals that have eaten plants.
The Phosphorus Cycle • Phosphorus may enter soil and water when rocks erode and may even move into the soil in small amounts in the form of phosphate (PO4)3-. • Plants absorb phosphates in the soil through their roots. • Some phosphorus washes off the land and ends up in the ocean. • Phosphate salts are not soluble in water and will sometimes sink to the bottom and accumulate as sediment.
The Phosphorus Cycle • Fertilizers used to stimulate and maximize plant growth contain nitrogen and phosphorus. • Excessive amounts of fertilizer can enter terrestrial, marine, and aquatic ecosystems through runoff. • Excess nitrogen and phosphorus can cause rapid algae growth – an algal bloom. • As massive amounts of rapidly produced algae begin to die off and settle, oxygen depletion becomes a problem for any organism relying on oxygen.
Acid Precipitation • When fuel is burned, large amounts of nitric oxide is released into the atmosphere. • In the air, nitric oxide can combine with oxygen and water vapor to form nitric acid. • Nitric acid then falls as acid precipitation.
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