Natural Cycles

2. respiration Animals use oxygen to break down sugars, fats, and proteins to release energy to live and grow.
5. Precipitation that flows over the surface of the soil.
7. dioxide Burning fossil fuels for energy releases this into the atmosphere.
10. The bumps on the roots of plants called legumes where nitrogen-fixing bacteria live.
11. Oxygen, carbon, nitrogen, and hydrogen cycle through non-living and living systems in a ________________ cycle.
13. The process in which plants make sugar using sunlight, water, and carbon dioxide and release oxygen into the atmosphere.
14. Water is absorbed by trees from the ground and released into the atmosphere.

1. Bacteria in the soil break down molecules containing nitrogen and nitrogen is returned to the atmosphere.
3. smog This is produced when sunlight interacts with air pollution to produce a brown smog.
4. This microscopic organism breaks down (eats) dead things.
6. A pollutant being released into the atmosphere.
8. The gathering of water into a body of water
9. fuel a source of energy (for example oil or coal) that is formed from dead plants and animals
12. fixation Nitrogen is combined with other elements by bacteria that live in plants.
15. precipitation Precipitation that is more acidic than normal due to pollution.