Phosphorus is one of the building units of nucleic acids and ATP. Plants absorb this element in the form of ions. It is utilized for the synthesis of plant tissues. This element comes back to the soil and water by the decomposition of dead and decayed organic matter and excretory products. From there it is again absorbed by the plants.
You have already studied how the O2 content is stabilised in the atmosphere. What about the quantity of water? How does the process of photosynthesis in plants, respiration and transpiration help in maintaining the cycle of O2 and water on the earth. Discuss and illustrate O2 and H2O cycles.
Sulphur is another element essential for the formation of tissues in plants and animals. In nature, the flow of this element is also cyclic.