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The nitrogen cycle - Khan Academy
网页2016年6月9日 · Bacteria play a key role in the nitrogen cycle. Nitrogen enters the living world by way of bacteria and other single-celled prokaryotes, which convert atmospheric nitrogen— N 2 —into biologically usable forms in a process called nitrogen fixation.
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网页Biogeochemical cycles are nature's way of recycling essential elements for life, like water, carbon, nitrogen, and phosphorus. These cycles circulate these molecules through ecosystems and the entire biosphere.
The water cycle (article) | Ecology | Khan Academy
网页Course: Biology archive > Unit 26. Lesson 7: Biogeochemical cycles. Intro to biogeochemical cycles. Biogeochemical cycles overview. The water cycle. The water cycle. The carbon cycle. The carbon cycle. The nitrogen cycle.
The water cycle - Khan Academy
网页The water cycle, powered by the sun, involves water moving in various forms between sources and sinks. It starts with evaporation from bodies of water, condensation into clouds, and precipitation back to the earth. This cycle also includes transpiration from plants and sublimation from ice to vapor.
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网页Watch a video explaining how nitrogen gas in the atmosphere is converted into usable forms for living organisms through the nitrogen cycle.
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The phosphorus cycle (article) | Ecology | Khan Academy
网页The slow cycling of phosphorus through the biosphere. How phosphorus-containing fertilizers can cause aquatic dead zones.
The carbon cycle (video) | Khan Academy
网页The carbon cycle involves plants taking in carbon dioxide, fixing carbon, and creating organic molecules. Animals eat plants, metabolize the molecules, and release carbon dioxide. This cycle keeps carbon circulating in the biosphere.
Photosynthesis | Biology archive | Science | Khan Academy
网页This unit is part of the Biology library. Browse videos, articles, and exercises by topic.