https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/v/biogeochemical-cycles 2024-05-06T19:22:43.24334365Z Biogeochemical cycles overview 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. From the water cycle to the carbon cycle, these processes ensure the constant reuse of matter, while energy flows through the ecosystem. Sal Khan video https://cdn.kastatic.org/googleusercontent/RkZfK_GfyQENMLzn91OXdJD-6fcWtW4iD5D2jYN8t2sSGSm9SmuUbQpyotrMYkzgCLJGmJfw0BnooTWMjSSGNWw Biogeochemical cycles overview 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. From the water cycle to the carbon cycle, these processes ensure the constant reuse of matter, while energy flows through the ecosystem. https://cdn.kastatic.org/ka-youtube-converted/ccWUDlKC3dE.mp4/ccWUDlKC3dE.mp4 475 Biogeochemical cycles https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/v/carbon-cycle 2024-05-06T19:22:43.24334365Z The carbon cycle Carbon is crucial for life, forming molecules like glucose, ATP, amino acids, and DNA. 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. Sal Khan video https://cdn.kastatic.org/googleusercontent/PANHGUsQ7xlmTUmBIQ5gOGmQph_QMC3IukyvEWtMqz7ynXac-nf0w-2gbg0-Lsah0_bhu8pJPMKf_GMxQJUfwO3B The carbon cycle Carbon is crucial for life, forming molecules like glucose, ATP, amino acids, and DNA. 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. https://cdn.kastatic.org/ka-youtube-converted/_dYkByQ9Kmg.mp4/_dYkByQ9Kmg.mp4 517 Biogeochemical cycles https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:energy-and-matter-in-biological-systems/x230b3ff252126bb6:biogeochemical-cycles/a/carbon-cycle 2026-04-29T10:50:35.589391704Z Learn: The carbon cycle Learn about the carbon cycle and how carbon moves between the biosphere and the geosphere. article https://www.khanacademy.org/science/ap-college-environmental-science/x0b0e430a38ebd23f:the-living-world-ecosystems-and-biodiversity/x0b0e430a38ebd23f:biogeochemical-cycles/a/the-carbon-cycle-article 2022-09-07T01:03:50.067296221Z The carbon cycle Review your understanding of the carbon cycle with this free article aligned to NGSS and AP standards. article https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/v/nitrogen-cycle 2024-05-06T19:22:43.24334365Z The nitrogen cycle 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 cycle also includes the return of nitrogen to the atmosphere through decomposition. Sal Khan video https://cdn.kastatic.org/googleusercontent/gQTO9JBwADmey2m_RcYCR_nTXRtFSeKzD8OmiRJn46LlNov4Q7sqsF2imvMCMS8i7OccArqSUWSxktBugc1seihb0g The nitrogen cycle 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 cycle also includes the return of nitrogen to the atmosphere through decomposition. https://cdn.kastatic.org/ka-youtube-converted/DsCMYyQ0NWU.mp4/DsCMYyQ0NWU.mp4 345 Biogeochemical cycles https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:energy-and-matter-in-biological-systems/x230b3ff252126bb6:biogeochemical-cycles/a/nitrogen-cycle 2026-04-29T11:20:48.686238051Z Learn: The nitrogen cycle Learn about the nitrogen cycle and how nitrogen moves from the atmosphere to living organisms through different chemical forms. article https://www.khanacademy.org/science/ap-college-environmental-science/x0b0e430a38ebd23f:the-living-world-ecosystems-and-biodiversity/x0b0e430a38ebd23f:biogeochemical-cycles/a/ap-es-the-nitrogen-cycle 2022-09-07T01:03:50.067296221Z The nitrogen cycle Review your understanding of the nitrogen cycle in this free article aligned to AP standards. article https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/v/phosphorous-cycle 2025-08-08T21:39:42.49220884Z Phosphorus cycle 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. Human activities like mining and farming can disrupt this cycle, leading to environmental consequences. Sal Khan video https://cdn.kastatic.org/googleusercontent/XOmOQvhgU1cxZJa1bTZG6AUTWtT3NjjcYTwch58xHeDlqoLG_2lhSOH6DZggQ4oOnFh8WVhlZjO3tGPBBuNCNd5h Phosphorus cycle 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. Human activities like mining and farming can disrupt this cycle, leading to environmental consequences. https://cdn.kastatic.org/ka-youtube-converted/tm2LG5ScT1g.mp4/tm2LG5ScT1g.mp4 331 Biogeochemical cycles https://www.khanacademy.org/science/ap-college-environmental-science/x0b0e430a38ebd23f:the-living-world-ecosystems-and-biodiversity/x0b0e430a38ebd23f:biogeochemical-cycles/a/ap-es-the-phosphorus-cycle 2022-09-07T01:03:50.067296221Z The phosphorus cycle Review your understanding of the phosphorus cycle in this free article aligned to AP standards. article https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/v/the-water-cycle 2024-05-06T19:22:43.24334365Z The water cycle 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. The majority of Earth's water is saltwater, with only a small percentage being freshwater in lakes, rivers, and groundwater. Sal Khan video https://cdn.kastatic.org/googleusercontent/okxRKXMHovcsPlENtDy06lBLXXn7tUYfX5eG7MOD5nZYSr_KyM9ufnRznemT6SbIP9tt1CNOA0D36g4_qHKE9eE The water cycle 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. The majority of Earth's water is saltwater, with only a small percentage being freshwater in lakes, rivers, and groundwater. https://cdn.kastatic.org/ka-youtube-converted/jFjI6y46QRk.mp4/jFjI6y46QRk.mp4 494 Biogeochemical cycles https://www.khanacademy.org/science/biology/ecology/biogeochemical-cycles/a/the-water-cycle 2025-08-08T21:39:42.49220884Z The water cycle Learn how water moves through Earth's ecosystems. article https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:energy-and-matter-in-biological-systems/x230b3ff252126bb6:biogeochemical-cycles/e/apply-the-carbon-cycle 2026-04-29T10:50:35.589391704Z Apply: The carbon cycle Apply your understanding about the carbon cycle in this set of free, standards-aligned practice questions. Wieteke Holthuijzen exercise https://www.khanacademy.org/science/hs-bio/x230b3ff252126bb6:energy-and-matter-in-biological-systems/x230b3ff252126bb6:biogeochemical-cycles/e/apply-the-nitrogen-cycle 2026-04-29T11:20:48.686238051Z Apply: The nitrogen cycle Apply your understanding about the nitrogen cycle in this set of free, standards-aligned practice questions. Wieteke Holthuijzen exercise https://www.khanacademy.org/science/ap-college-environmental-science/x0b0e430a38ebd23f:the-living-world-ecosystems-and-biodiversity/x0b0e430a38ebd23f:biogeochemical-cycles/e/biogeochemical-cycles-exercise 2025-03-05T16:58:16.378047616Z Biogeochemical cycles Apply your understanding of biogeochemical cycles in this set of free practice questions aligned to AP standards. exercise