CHAPTER 5 , SECTION 2

The Cycling of Materials

The Carbon Cycle

The Carbon Cycle

Carbon is an essential component of proteins, fats, and carbohydrates, which make up all organisms.

The carbon cycle is a process by which carbon is cycled between the atmosphere, land, water, and organisms.

The Carbon Cycle

The Carbon Cycle: Short-Term

Producers convert carbon dioxide in the atmosphere into carbohydrates during photosynthesis.

Consumers eat producers and obtain carbon from the carbohydrates.

During cellular respiration, some of the carbon is released back into the atmosphere as carbon dioxide.

The Carbon Cycle: Long-Term

Carbon can be converted into carbonates. Bones, shells, limestone rock

Carbon can be converted into molecules that store energy. Fats and oils This carbon is not released until the organism dies. These dead organisms form coal, oil, and natural gas.

How Humans Affect the Carbon Cycle

We alter the carbon cycle by… Clear trees and plants that absorb CO2 through

photosynthesis faster than they can grow back Add large amounts of CO2 by burning fossil fuels

and wood.Increased concentrations of can enhance the

planet’s natural greenhouse effect. Global warming disrupts global food production

and wildlife habitats, alter temperature and precipitation patterns, and raise the average sea level in various parts of the world.

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The Nitrogen Cycle

The Nitrogen Cycle

All organisms need nitrogen to build proteins which are used to build new cells.

Nitrogen makes up 78% of the gases in the atmosphere.

Most organisms cannot use atmospheric nitrogen.

The Nitrogen Cycle

Nitrogen-fixing bacteria are the only organisms than can convert bacteria into usable chemical compounds.

Nitrogen-fixing bacteria live on the roots of legumes. Use sugars to produce nitrogen-containing

compounds. Excess nitrogen is released into the soil

The Nitrogen Cycle

All other organisms depend on these bacteria to supply the nitrogen they need for survival.

Animals get nitrogen from eating plants or other animals that contain usable sources of nitrogen.

The nitrogen cycle is a process in which nitrogen is cycled between the atmosphere, bacteria, and other organisms.

The Nitrogen Cycle

Decomposers and the Nitrogen Cycle

Decomposers break down wastes and decaying organisms to return nitrogen to the soil.

If decomposers did not exist, nitrogen would be stored forever in wastes and corpses.

Effects of Human Activities on the Nitrogen Cycle

We add large amounts of nitric oxide (NO) into the atmosphere when N2 and O2 combine as we burn any fuel at high temperatures. This gas can be converted to nitrogen dioxide

gas (NO2) and nitric acid (HNO3) which can return to the Earth’s surface as acid rain.

We add nitrous oxide (N2O) to the atmosphere through the action of anaerobic bacteria on livestock wastes and commercial inorganic fertilizers applied to soil. This gas can warm the atmosphere and deplete

ozone in the stratosphere.

Effects of Human Activities on the Nitrogen Cycle

Nitrate ions in inorganic fertilizers can leach through the soil and contaminate groundwater. This is harmful to drink, especially for infants and

small children.

We release large quantities of nitrogen stored in soils and plants as gaseous compounds into the troposphere through destruction of forests, grasslands, and wetlands.

We upset aquatic ecosystems by adding excess nitrates to bodies of water through agricultural runoff and discharges from municipal waste systems.

Effects of Human Activities on the Nitrogen Cycle

We remove nitrogen from topsoil when we harvest nitrogen-rich crops, irrigate crops, and burn or clear grasslands and forests before planting crops.

Since 1950 human activities have more than doubled the annual release of nitrogen from the terrestrial portion of the earth into the rest of the environment.

This is a serious local, regional, and global environmental problem that has attracted little attention when compared to global warming and depletion of the ozone layer.

The Phosphorus Cycle

The Phosphorus Cycle

Phosphorus is needed to form bones and teeth.

Plants get phosphorus from soil and water.

Animals get phosphorus from eating plants or other animals who have eaten plants.

The phosphorus cycle is the movement of phosphorus from the environment to organisms and then back to the environment.

The Phosphorus Cycle

Phosphorus may enter soil When rocks erode, phosphorus dissolves in soil and

water. Plants absorb the phosphates through their roots.

Phosphorus is added to soil and water when excess phosphorus is excreted in waste or when organisms die and decompose.

Phosphorus washes off the land and ends up in the ocean. These phosphate salts sink to the bottom of the ocean and accumulate as sediment.

The Phosphorus Cycle

Effects of Human Activities on the Phosphorous Cycle

We mine large quantities of phosphate rock to make commercial inorganic fertilizers and detergents.

We reduce the available phosphate in tropical soils when we cut down areas of tropical forests.

We disrupt aquatic systems with phosphates from runoff of animal wastes and fertilizers and discharges from sewage treatment systems.

Human activities have increased the natural rate of phosphorous about 3.7 times since 1900.

Summary Questions

1. How can driving a car affect the carbon cycle?

2. Explain how the excessive use of fertilizer affects the nitrogen cycle and the phosphorus cycle.

3. Explain why the phosphorus cycle occurs more slowly than both the carbon cycle and the nitrogen cycle.