2. The carbon cycle Trace the pathways through which carbon is released and absorbed in the diagram below:

3. Nitrogen is important to living things because it is used to make amino acids, the building blocks of all proteins. Approximately 78 percent of Earth’s atmosphere is nitrogen gas (N 2 ). The nitrogen cycle

4. Phosphorus is essential for cell replication, metabolism, and structures. Phosphorus from minerals is absorbed by the roots for use by the plant. Animals obtain phosphorus by eating plants. The phosphorus cycle

5. The Potassium Cycle Animal manures and biosolids Mineral fertilizers Crop harvest Runoff and erosion Leaching Soil solution potassium (K + ) Plant residues Plant uptake Mineral potassium Fixed potassium Exchangeable potassium Input to soil Component Loss from soil

6. The Sulfur Cycle Animal manures and biosolids Mineral fertilizers Crop harvest Runoff and erosion Leaching Absorbed or mineral sulfur Plant residues Plant uptake Sulfate Sulfur (SO 4 ) Atmospheric sulfur Elemental sulfur Organic sulfur Immobilization Mineralization Bacterial reduction Bacterial oxidation Oxidation SO 2 gas Reduced sulfur Input to soil Component Loss from soil Volatilization Atmospheric deposition -

7. On your computer check this out! http://climate.nasa.gov/