CYCLING IN THE
ECOSYSTEM
pp. 371-374
DEFINITIONS
• Ecosystem: an environment where the
living (biotic) and non-living (abiotic)
things affect one another
• Biogeochemical process: circulation of
substances through living organisms and
the environment
WATER CYCLE
• Evaporation: water vapor enters the
atmosphere
• Transpiration: evaporation of water through
the leaves of plants
• Precipitation: water vapor that leaves the
atmosphere
CARBON CYCLE
• Photosynthesis: converting light energy into
organic compounds
• Cellular respiration: breaking down organic
compounds to release energy
• Combustion: burning of fossil fuels for
energy releases CO2
NITROGEN CYCLE
• nitrogen fixation: bacteria convert nitrogen
gas to usable form (ammonia)
• ammonification: decomposers break down
proteins/nucleic acids to ammonia
• nitrification: bacteria convert ammonia to
nitrates (fertilizers)
• assimilation: plants take up nitrates to make
proteins
• denitrification: bacteria return nitrogen to
atmosphere
PHOSPHORUS CYCLE
• Weathering: Erosion of rocks
• Decomposition: breaking down organic
compounds
• Absorption: Plants absorb phosphates from
soil and water
• Runoff: Phosphates from fertilizers or soaps
washes from land into water bodies