BIOLOGY
Class Notes
9-3
Aim: Cycles of Matter
***ENERGY IS NOT RECYCLED IN AN ECOSYSTEM, MATTER IS.***
(A) WATER
 Cells are 70-90% water
 Water is necessary for metabolic processes
 Steps in the water cycle:
o Evaporation—water loss from lakes, rivers, oceans…. And
Transpiration –water loss from plants
Condensation—water vapor forms clouds
Precipitation—water returns to earth as sleet,
rain, snow
Surface runoff—returns water to bodies of
water or to groundwater
(B) CARBON CYCLE
 Consists of photosynthesis, cellular respiration and
decomposition


Begins with producers taking carbon dioxide from the air
during photosynthesis
Steps in the carbon cycle:
Plants take in carbon dioxide from the air
Plants store carbon in the food they make during photosynthesis
Plants and animals release carbon dioxide back into the air during cellular
respiration
Decomposers return carbon to the environment
(C) NITROGEN
 Needed by all organisms
 Used to make proteins and nucleic acids which make up DNA
and RNA
 Air is made up of about 80% nitrogen
 Steps in the nitrogen cycle:
Bacteria convert the nitrogen in the air into nitrates
Plants can absorb and use nitrate to make proteins
Consumers eat plants and get proteins containing nitrogen
Decomposers break down dead organisms and return nitrogen to
air