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Learn about the nitrogen cycle, its importance to ecosystems, and how it works.
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The water cycle - Khan Academy
These include carbon, nitrogen, phosphorus, and sulfur. In particular, surface runoff helps move elements from terrestrial, land-based, to aquatic ecosystems. We'll take a closer look at how this works in the following articles, where we'll examine different elements' biogeochemical cycles.
The nitrogen cycle (video) | Khan Academy
The nitrogen cycle is a crucial process that converts atmospheric nitrogen into a form that plants and other organisms can use. This process, known as nitrogen fixation, is primarily carried out by bacteria. Nitrogen is essential for life, forming a key component in amino acids, ATP, and DNA.
The water cycle - Khan Academy
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.
Phosphorus cycle (video) | Khan Academy
The phosphorus cycle, essential for life, involves the movement of phosphorus atoms from rocks and soil into plants and animals. Unlike carbon or nitrogen, phosphorus doesn't exist in the atmosphere. It's often a limiting factor for plant growth, making it a key ingredient in fertilizers.
The Calvin cycle - Khan Academy
In the Calvin cycle, carbon atoms from CO 2 are fixed (incorporated into organic molecules) and used to build three-carbon sugars. This process is fueled by, and dependent on, ATP and NADPH from the light reactions.
Phases of the cell cycle - Khan Academy
The cell cycle can be thought of as the life cycle of a cell. In other words, it is the series of growth and development steps a cell undergoes between its “birth”—formation by the division of a mother cell—and reproduction—division to make two new daughter cells.
The water cycle (article) | The water cycle | Khan Academy
Review your understanding of the water cycle in this free article aligned to NGSS standards. Key points: The water cycle describes how water continuously moves between Earth’s surface and the atmosphere.
Cell cycle regulators - Khan Academy
Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks). A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify target proteins.