Download Cycling of Materials in Ecosystems

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 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