Biogeochemical Cycles:

Biotic vs. Abiotic Biotic factors – all the living parts of an ecosystem like plants, animals, and decomposers. Abiotic factors – all of the non-living things that affect the ecosystem like rainfall, rocks, clouds, water, wind, and minerals.

The Water Cycle: Water is crucial to every living thing on the planet. It covers ~75% of earth and composes about ~75% of our body mass.

The Carbon Cycle: All living things on this planet are carbon-based. Photosynthesis and cellular respiration is the basis for the carbon cycle. Plants use CO2 for photosynthesis to make carbohydrates Many organisms use oxygen to break down carbohydrates for energy during cellular respiration Humans have increased the concentration of CO2 in the atmosphere by 30%

The Nitrogen Cycle: All organisms need nitrogen to make proteins and nucleic acids. Consumers get that nitrogen by eating plants or other consumers. Plants must get the nitrogen from the environment. They cannot absorb it through the air, it must be absorbed as nitrate in the soil. Nitrogen-fixing bacteria convert the gas to nitrate the plants can use – called nitrogen fixation Urine and dung also contain nitrogen that can be used.

Nitrogen Fixation Bacteria convert the gas to ammonia then to nitrite then to nitrate Ammonification – decomposers convert urine, dung, and dead things into ammonia which can be reused by the ecosystem Nitrification – bacteria taking ammonia and turning into nitrites then nitrates Denitrification – anaerobic bacteria returning nitrogen gas to the atmosphere

The Phosphorus Cycle: Phosphorus is needed by organisms for DNA, phospholipids (cell membranes), and bones, teeth and shells of animals. Most phosphorus comes from phosphate salts from rocks and deposited into water Humans add lots more phosphate to water by fertilizer runoff and surface mining and reduce phosphate by cutting forests.