Q.Write short notes on the following: (A) Phosphorus cycle (B) Primary immunity.

(A) Phosphorus cycle is a sedimentary nutrient cycle with rock as reservoir and no gaseous phase; (B) primary immune response is the slow, low-intensity response on first antigen exposure that creates memory cells.

(A) Phosphorus cycle:

• Phosphorus is a major constituent of biological membranes, nucleic acids (DNA, RNA) and cellular energy transfer molecules (ATP).
• It is a sedimentary cycle; the natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.
• When rocks are weathered, small amounts of these phosphates dissolve in soil solution and are absorbed by the roots of plants.
• Herbivores and other animals obtain phosphorus by eating plants.
• The waste products and dead organisms are decomposed by phosphate-solubilising bacteria, releasing phosphorus back into the soil.
• Unlike the carbon and nitrogen cycles, there is no significant respiratory (gaseous) release of phosphorus into the atmosphere.

(B) Primary immunity (Primary immune response):

• When the body encounters a pathogen (antigen) for the first time, it produces a response called the primary immune response.
• This response is comparatively slow and of low intensity; it takes several days to build up. …