Ecology
Chapter 3, section 3.2
•
•
Name: ______________________________
NOTES
The Cycling of Materials
Materials in the ecosystem are used again and again; otherwise, they would be gone, and life could no longer
exist.
This section covers three different cycles that allow materials to be reused.
THE WATER CYCLE
THE CARBON CYCLE
THE NITROGEN CYCLE
The Water Cycle & Draw and color diagram 3-10
• Water is essential to life.
• The sun provides the energy that drives the water cycle.
ex: Heat from the sun evaporates water from the Earth. As the water vapor cools in the atmosphere, it
condenses, forms droplets in the clouds. When the clouds meet cold air, the water returns to Earth as
precipitation (rain, sleet, snow.)
• Some of the water goes through the cycle again, other seeps into the ground or flows back to the ocean via rivers
and streams.
The Carbon Cycle & Draw and color diagram 3-11
• Carbon is the essential component of the proteins, fats, and carbohydrates necessary for life.
• Carbon enters an ecosystems when producers take in CO2 from the atmosphere during photosynthesis.
• Consumers eat the producers, obtaining carbon.
• Consumers break down the food molecules during cellular respiration and release carbon back into the
atmosphere as CO2.
• Photosynthetic organisms also release CO2 during cellular respiration.
How Humans are affecting the Carbon Cycle
• Fossil fuels (coal, oil, natural gas) are essentially stored carbon.
• They are left over from the bodies of plants and animals that died millions of years ago and were trapped
underground.
• When we burn fossil fuels, we release carbon into the atmosphere as CO2.
• Problem: We burn such large quantities of fossil fuels; we are increasing the CO2 levels in the atmosphere
The Nitrogen Cycle & Draw and color diagram 3-13
• All organisms need nitrogen to build proteins.
• There are vast quantities around us; nitrogen gas makes up 78% of the atmosphere.
• Nitrogen-fixing bacteria are the only organism that can use nitrogen gas directly from the atmosphere. All other
organisms depend upon these bacteria for their nitrogen.
• These bacteria take nitrogen gas from the air and transform, or “fix,” it into a form that ecosystems can use.
• Nitrogen-fixing bacteria live within the roots of a few plants (beans, peas, clover, alder trees) and in the soil. They
both release nitrogen into the soil.
• Animals obtain nitrogen through consumption of plants or other animals.
Closing the Nitrogen Cycle
• In the nitrogen cycle, nitrogen moves back and forth between the atmosphere and living things.
• Decomposers, such as fungi and bacteria, return nitrogen to the soil by breaking down dead organisms and waste
products (urine, dung, leaves, and other plant parts.)
• After decomposers return the nitrogen to the soil, some nitrogen is converted into a usable form of nitrogen for
plants and other bacteria transform a small amount into nitrogen gas, returning it back into the atmosphere,
completing the nitrogen cycle.
• Once nitrogen enters an ecosystem, most of it stays within the ecosystem, cycling between organisms and the soil
in an endless loop.