| A | B |
|---|
| food chain | a series of steps in which organisms transfer energy by eating and being eaten |
| phytoplankton | a mixture of floating algae |
| food web | a network of feeding interactions |
| zooplankton | diverse group of small swimming animals that feed on algae |
| trophic level | each step in a food chain |
| ecological pyramids | show the relative amout of energy or matter contained within each trophic level |
| biomass | total amount of living tissue within a trophic level |
| biogeochemical cycles | how elements are passed in the biosphere through closed loops powered by the flow of energy |
| nutrients | chemical substances an organism needs to sustain life |
| nitrogen fixation | certain bacteria convert nitrogen gas to ammonia |
| denitrification | process by which bacteria convert nitrates into nitrogen gas |
| limiting nutrient | the nutrient whose supply limits productivity |
| evaporation | liquid water is changed to vapor form |
| runoff | precipitation that enters a river or stream |
| groundwater | precipitation absorbed into soil |
| transpiration | evaporation from the leaves of plants |
| precipitation | rain, snow, sleet, hail |
| condensation | water vapor cools into liquid droplets |
