The Nitrogen CycleThe Nitrogen Cycle

Another Cycle in Nature…Another Cycle in Nature…

• Nitrogen is an element found in living Nitrogen is an element found in living plants and animals.plants and animals.

• Nitrogen is also found in nonliving Nitrogen is also found in nonliving things like the atmosphere and soil.things like the atmosphere and soil.

• The slow movement of nitrogen The slow movement of nitrogen between living things, dead things, between living things, dead things, the air, the soil, and water is called the air, the soil, and water is called the nitrogen cycle.the nitrogen cycle.

The Nitrogen CycleThe Nitrogen Cycle

What is it? Where is it What is it? Where is it found?found?

• Most of the nitrogen on Earth is in the Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of the atmosphere. Approximately 80% of the molecules in Earth's atmosphere are molecules in Earth's atmosphere are made of two nitrogen atoms bonded made of two nitrogen atoms bonded together (N2).together (N2).

• All plants and animals need nitrogen to All plants and animals need nitrogen to make amino acids, proteins, and DNA, but make amino acids, proteins, and DNA, but the nitrogen in the atmosphere is not in a the nitrogen in the atmosphere is not in a form that they can use.form that they can use.

NN2 2 for You!for You!

• The molecules of nitrogen in the The molecules of nitrogen in the atmosphere can become usable for atmosphere can become usable for living things when they are broken apart living things when they are broken apart during lightning strikes or fires, by during lightning strikes or fires, by certain types of bacteria, or by bacteria certain types of bacteria, or by bacteria associated with bean plants.associated with bean plants.

• Most plants get the nitrogen they need Most plants get the nitrogen they need to grow from the soils or water in which to grow from the soils or water in which they live. they live.

NN2 2 for You!for You!

• Animals get the nitrogen they need by eating Animals get the nitrogen they need by eating plants or other animals that contain nitrogen.plants or other animals that contain nitrogen.

• When organisms die their bodies decompose When organisms die their bodies decompose bringing the nitrogen into soil on land or into bringing the nitrogen into soil on land or into ocean water. ocean water.

• Bacteria alter the nitrogen into a form that Bacteria alter the nitrogen into a form that plants are able to use. Other types of plants are able to use. Other types of bacteria are able to change nitrogen bacteria are able to change nitrogen dissolved in waterways into a form that dissolved in waterways into a form that allows it to return to the atmosphere.allows it to return to the atmosphere.

Too Much NToo Much N22!!• Certain actions of humans are causing changes to Certain actions of humans are causing changes to

the nitrogen cycle and the amount of nitrogen that the nitrogen cycle and the amount of nitrogen that is stored in the land, water, air, and organisms.is stored in the land, water, air, and organisms.

• The use of nitrogen-rich fertilizers can add too The use of nitrogen-rich fertilizers can add too much nitrogen in nearby waterways as the fertilizer much nitrogen in nearby waterways as the fertilizer washes into streams and ponds. washes into streams and ponds.

• The waste associated with livestock farming also The waste associated with livestock farming also adds large amounts of nitrogen into soil and water. adds large amounts of nitrogen into soil and water. The increased nitrate levels cause plants to grow The increased nitrate levels cause plants to grow rapidly until they use up the supply and die rapidly until they use up the supply and die (eutrophication). The numbers of plant-eating (eutrophication). The numbers of plant-eating animals will increase when the plant supply animals will increase when the plant supply increases and then the animals are left without any increases and then the animals are left without any food when the plants die.food when the plants die.

More Problems with NMore Problems with N22!!• Lakes are clogged with aquatic weeds. Lakes are clogged with aquatic weeds.

“Dead Zones” have formed in areas of the “Dead Zones” have formed in areas of the oceans where animals cannot survive. Air oceans where animals cannot survive. Air pollutants that contain nitrogen decreasing pollutants that contain nitrogen decreasing air quality and greenhouse gases that contain air quality and greenhouse gases that contain nitrogen are becoming more common.nitrogen are becoming more common.

• Nitrogen dioxide (NONitrogen dioxide (NO22) and nitric oxide (NO) ) and nitric oxide (NO) molecules form during combustion in car molecules form during combustion in car engines, power plants, and factories.engines, power plants, and factories.