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“Cycles” KEY CONCEPT: Matter cycles in and out of an ecosystem. The Water Cycle The water cycle is the circular pathway of water on Earth. The Water Cycle The movement of water between the oceans, atmosphere, land, and living things is known as the water cycle. How Water Moves During evaporation, the sun’s heat causes water to change from liquid to vapor. In the process of condensation, the water vapor cools and returns to a liquid state. The water that falls from the atmosphere to the land and oceans is called precipitation. Rain, snow, sleet, and hail are all forms of precipitation. Most precipitation falls into the ocean. The precipitation that falls on the land and flows into streams, rivers, and lakes is called runoff. Groundwater is precipitation that seeps into the ground and is stored between or within rocks. Groundwater slowly flows back into the soil, streams, rivers, and oceans. Oxygen Cycle: Plants make food by photosynthesis They use carbon dioxide (CO2) to make oxygen (O2) Animals breathe out carbon by respiration They use oxygen (O2) and breathe out carbon dioxide (CO2) –By the way … humans are animals too Water and Life Without water, there would be no life on Earth. All organisms, from bacteria to animals and plants, are composed mostly of water. Water helps transport nutrients and waste within an organism. Water helps regulate temperature. All water taken in by an organism is eventually returned to the environment. Example: Oxygen Cycle: oxygen photosynthesis respiration carbon dioxide Carbon Cycle Carbon is the building block of life. a. The carbon cycle moves carbon from the atmosphere, through the food web, and returns to the atmosphere. b. Carbon is emitted by the burning of fossil fuels (like oil, gasoline, and coal) Carbon Cycle: notice photosynthesis and respiration are back … they both involve CO2 (now we’re looking at the C for carbon) carbon dioxide in air combustion respiration photosynthesis respiration decomposition of organisms fossil fuels photosynthesis carbon dioxide dissolved in water The Carbon Cycle Besides water, the most common molecules in living things are organic molecules, or molecules that contain carbon. The exchange of carbon between the environment and living things is known as the carbon cycle. Decomposition and Combustion The breakdown of substances into simpler molecules is called decomposition. For example, when fungi and bacteria decompose organic matter, carbon dioxide and water are returned to the environment. Combustion is the process of burning a substance, such as wood or fossil fuels. Combustion of organic matter releases carbon. The Nitrogen Cycle Living things need nitrogen to build proteins and DNA. The movement of nitrogen between the environment and living things is called the nitrogen cycle. The nitrogen cycle mostly takes place underground. Some nitrogen fixing bacteria live in nodules on the roots of plants; others live freely in the soil. Converting Nitrogen Gas Although about 78% of the Earth’s atmosphere is nitrogen gas. Most organisms cannot use nitrogen gas directly. Bacteria in the soil are able to change nitrogen gas into forms that plants can use. This process is called nitrogen fixation. Other organisms get the nitrogen they need by eating plants or animals that eat plants. Passing It On When organisms die, decomposers break down the remains. Decomposition releases a form of nitrogen into the soil that plants can use. Certain types of bacteria in the soil convert nitrogen to a gas, which is returned to the atmosphere.