Cycling of Materials in EcosystemsSECTION 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 CO2 from the air and converts it into food molecules

Three processes return CO2 to the air:

1. Cellular respiration – animals exhale CO2 as a waste product

2. Combustion – burning plants or fossil fuels releases CO2

3. Erosion – the breakdown of shells made by marine organisms releases CO2

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