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Natural Cycles What materials are cycled through the Earth’s ecosystems? How do living things get the materials they need? Earth’s Resources Ecosystems depend on energy from the sun and different natural cycles. The Water Cycle The Carbon-DioxideOxygen Cycle The Nitrogen Cycle The Water Cycle The movement of water through Earth’s ecosystems is the water cycle. Water falls to Earth as precipitation and is used by plants and animals. Animals return the water as waste. Plants absorb the water through their roots and dismiss the water through their leaves (transpiration). The Water Cycle Energy from the sun causes the water to change from liquid to vapor (evaporation). Water vapor changes from gas to liquid through condensation. Precipitation returns water to the Earth. Precipitation that goes into the ground is called groundwater. Groundwater used by the plants is called transpiration. The Carbon Dioxide-Oxygen Cycle The Carbon DioxideOxygen cycle is powered by the sun. Photosynthesis occurs in plants because plants take in carbon dioxide and release oxygen. Gases are balanced in the air. Decomposers use oxygen and produce carbon dioxide. Some animals produce carbon dioxide as waste. The Nitrogen Cycle The movement of nitrogen through the ecosystem is called the nitrogen cycle. Nitrogen makes up 78% of the air. Nitrogen is used and returned by living things. Bacteria converts nitrogen into compounds that can be used by organisms to build proteins. Summary The water cycle is powered by the energy of the sun. Water evaporates and then condenses forming clouds. Clouds return the water as precipitation. In the carbon dioxide-oxygen cycle, photosynthesis uses carbon dioxide and produces oxygen. The nitrogen cycle depends on bacteria that convert nitrogen to nitrogen compounds that are used by organisms.
