https://www.khanacademy.org/science/middle-school-earth-and-space-science/x87d03b443efbea0a:weather-and-climate/x87d03b443efbea0a:the-water-cycle/v/the-water-cycle-ms 2022-09-10T03:34:09.940758862Z The water cycle In the water cycle, water continuously moves between Earth's surface and the atmosphere. This occurs through processes such as evaporation and transpiration, condensation, and precipitation. The water cycle is driven by solar energy and gravity. Khan Academy video https://cdn.kastatic.org/ka_thumbnails_cache/1762ab92-ad00-4c89-93c8-e21ef6184153_1280_720_base.png The water cycle In the water cycle, water continuously moves between Earth's surface and the atmosphere. This occurs through processes such as evaporation and transpiration, condensation, and precipitation. The water cycle is driven by solar energy and gravity. https://cdn.kastatic.org/ka-youtube-converted/r2dnUvP1JgM.mp4/r2dnUvP1JgM.mp4 267 Biogeochemical Cycles https://www.khanacademy.org/science/bmc-grade-9-science/x345505a97fc4a662:energy-flow-in-an-ecosystem/x345505a97fc4a662:bio-geo-chemical-cycle/v/the-carbon-cycle 2025-07-01T18:08:15.179962416Z The carbon cycle Carbon moves through the environment in a continuous cycle, shifting between reservoirs such as plants, animals, soil, air, water, and rocks. Key processes—photosynthesis, respiration, decomposition, and combustion—drive this movement. While the biological carbon cycle happens quickly, the geological carbon cycle takes millions of years. Human actions can disrupt this cycle, contributing to climate change. Mahesh Shenoy video https://cdn.kastatic.org/ka_thumbnails_cache/45df2542-dadf-4897-977d-715d87892a21_1280_720_base.png The carbon cycle Carbon moves through the environment in a continuous cycle, shifting between reservoirs such as plants, animals, soil, air, water, and rocks. Key processes—photosynthesis, respiration, decomposition, and combustion—drive this movement. While the biological carbon cycle happens quickly, the geological carbon cycle takes millions of years. Human actions can disrupt this cycle, contributing to climate change. https://cdn.kastatic.org/ka-youtube-converted/XynPVsE1fd4.mp4/XynPVsE1fd4.mp4 284 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/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/revision-term-2-tg-biology-class-8/x04828215b460a495:week-2/x04828215b460a495:the-world-of-microorganisms-part-i-ii/v/nitrogen-cycle-middle-school-science-khan-academy 2025-03-06T03:29:07.687997642Z Nitrogen Cycle Did you know that nitrogen keeps moving through the air, soil, plants, and animals in a never-ending cycle? Shankar Nair video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Nitrogen Cycle Did you know that nitrogen keeps moving through the air, soil, plants, and animals in a never-ending cycle? https://cdn.kastatic.org/ka-youtube-converted/rDFVzVOkcPs.mp4/rDFVzVOkcPs.mp4 256 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/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/bmc-grade-9-science/x345505a97fc4a662:energy-flow-in-an-ecosystem/x345505a97fc4a662:bio-geo-chemical-cycle/v/oxygen-cycle 2026-02-28T16:20:46.436623441Z Oxygen Cycle Learn about the Oxygen Cycle and understand how living (biotic) and non-living (abiotic) processes create and consume oxygen. A clear middle school explanation with examples and summary. Khan Academy video https://cdn.kastatic.org/googleusercontent/ZCdwTudJg6e6n-P2gsaUborP4izvMsGo71pvEVlX9dNYWcLXcP7VHkWpn2grt4TUP1KoJLQP9NswyHBuBLSFTBw Oxygen Cycle Learn about the Oxygen Cycle and understand how living (biotic) and non-living (abiotic) processes create and consume oxygen. A clear middle school explanation with examples and summary. https://cdn.kastatic.org/ka-youtube-converted/ilVmoLQFsMA.mp4/ilVmoLQFsMA.mp4 311 Biogeochemical Cycles 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 https://www.khanacademy.org/science/how-we-interact-with-our-environment/x049400914d70a1b7:ecosystem/x049400914d70a1b7:nutrient-cycling/e/hs-biogeochemical-cycles 2026-04-08T00:16:02.937952483Z Biogeochemical cycles Test your knowledge of the water cycle, carbon cycle, and nitrogen cycle! Ashley exercise