1. Carbon Cycle
Biological Significance: Carbon is the key component in all organic molecules. These are the essence of life!
>Photosynthesis: 6CO2 + 6H2O C6H12O6 + 6O2
Plants, algae, some bacteria, & some protists
>Cellular respiration: C6H12O6 + 6O H2O + 6CO2 + ATP (energy)
All organisms
Reservoirs: Short term: Atmosphere, oceans (dissolved and in sediment, and organisms Long term: The lithosphere (fossil fuels, rocks and carbonate minerals)
Assimilation: Plants take in carbon from the atmosphere in photosynthesis. Other organisms take in carbon by eating plants or other organisms. Decay recycles carbon.
sunlight

2. Nitrogen Cycle
Biological Significance: Nitrogen is essential for nucleic acids (DNA & RNA), amino acids (the monomers of proteins), and chlorophyll (necessary for photosynthesis) .
Nitrification, ammonification, denitrification.
Reservoirs: Atmosphere (N2), soil and aquatic sediments (NH3, NH4+, NO2+, NO3+)
Assimilation: Bacteria in the soil, water and roots of plants fix free nitrogen (makes it usable). Organisms eat plants or other organisms. Waste and decay recycle nitrogen as either ammonia compounds (ammonification) or free nitrogen (denitrification).

3. Phosphorus Cycle
Biological Significance: Phosphorus is essential for nucleic acids (DNA & RNA, phospholipids (make up cell membranes), and ATP (energy).
Reservoirs: Lithosphere (soils and marine sedimentary rock), oceans, and organisms. VERY LITTLE IN THE ATMOSPHERE!
Assimilation: Enters plants from the soil as soluble phosphate. Organisms eat plants or other organisms. Decay recycles phosphorus.