Biogeochemical Cycles Biogeochemical cycles Recycling in the biosphere

Biogeochemical Cycles

Biogeochemical cycles • Recycling in the biosphere: – Water cycle – Nitrogen cycle – Carbon cycle

Water Cycle • Water cycles between the atmosphere and the • earth Made up of several parts: – – – Evaporation (and transpiration) Condensation Precipitation Runoff Seepage Root uptake

Water Cycle • Evaporation: liquid gas (vapor) – Transpiration: evaporation of water from plants • Condensation: gas liquid • Precipitation: water falling to the Earth in the form of rain, snow, sleet, or hail

Water Cycle • Runoff: water that runs along the surface of the ground until it enters a river or stream • Seepage: when rain seeps into the soil • Root uptake: water in soil enters plants through roots

Carbon Cycle § Carbon exists in the nonliving (abiotic) environment as: – carbon dioxide (CO 2) in the atmosphere and dissolved in water – carbonate rocks – deposits of coal, petroleum, and natural gas derived from once-living things – dead organic matter

Carbon Cycle § Carbon enters the biotic world through the action of autotrophs and heterotrophs – Photosynthesis (autotrophs) – Respiration (heterotrophs) – Burning – Decay

The Carbon Cycle CO 2 in Atmosphere CO 2 in Ocean Go to Section:

Nitrogen Cycle n n All life requires nitrogen-compounds, e. g. , proteins and nucleic acids. Air, which is 79% nitrogen gas (N 2), is the major reservoir of nitrogen. – But most organisms cannot use nitrogen in this form. Plants must secure their nitrogen in a "fixed" form, such as: – nitrate ions (NO 3−) – ammonia (NH 3) – urea (NH 2)2 CO Animals get their nitrogen compounds from feeding on plants or animals that eat plants

Nitrogen Cycle n Four processes participate in the cycling of nitrogen through the biosphere: – Nitrogen fixation: conversion of nitrogen gas into ammonia – Nitrification: conversion of ammonia into nitrates and nitrites n Producers can use them to make proteins n Consumers then eat producers and reuse nitrogen to make their own proteins – Denitrification: conversion of nitrates into nitrogen gas – Decay: decomposers break down dead organisms and return nitrogen to the soil as ammonia n Bacteria play major roles in all four of these.

N 2 in Atmosphere NO 3 and NO 2 NH 3 Go to Section: