Cycling of Materials in Ecosystems SECTION 16.3

Biogeochemical Cycles A pathway from living things, into nonliving parts of the ecosystem and back All matter on Earth has been here as long as the planet has – this matter is recycled over and over again This is the law of conservation: matter cannot be created or destroyed, only changed Four important cycles: 1.Water 2.Carbon 3.Nitrogen 4.phosphorus

The water cycle Water is the most important – all life on Earth depends on water Water on Earth exists in all three states – solid (ice), liquid, and gas (water vapor) Precipitation – water from the atmosphere to the surface (solid or liquid) ◦Ground water – below the surface ◦Surface water – lakes, rivers, oceans ◦Absorption – taken up by living things Evaporation – water from the surface back to the atmosphere ◦Transpiration – evaporation from the leaves of plants

The Carbon Cycle Life on Earth is based on carbon molecules – our bodies are made of carbon Photosynthesis – takes CO 2 from the air and converts it into food molecules Three processes return CO 2 to the air: 1.Cellular respiration – animals exhale CO 2 as a waste product 2.Combustion – burning plants or fossil fuels releases CO 2 3.Erosion – the breakdown of shells made by marine organisms releases CO 2

The Nitrogen Cycle Nitrogen is an important molecule in proteins and DNA About 78% of the atmosphere is nitrogen, but it is not in a form living things can absorb Nitrogen-fixing bacteria which live on the roots of certain plants convert atmospheric nitrogen to a form plants can absorb From there it enters the food chain It is returned to the atmosphere by decomposition of wastes and dead organisms

The Phosphorus Cycle Phosphorus is an important part of DNA and the energy molecule ATP This cycle is different from the others because phosphorus never enters the atmosphere It is absorbs from the ground into plants and enters the food chain. Then it is returned to the soil during decomposition