Describe the model of phosphorus cycle in the terrestrial ecosystem.

OR

Describe the DDT biomagnification occurring in an aquatic food chain. State the negative effects the process has on the organisms at the last trophic level of the food chain.

Phosphorous is the key element in the phosphorous cycle. Characteristics of phosphorus cycling in ecosystem were attributed to factors such as the source of phosphorus, the chemical form, traits in soils and the complexity of its controlling factors. Phosphorus in terrestrial ecosystems is derived mainly from weathering of rocks, biological and chemical processes, such as microbial absorption, precipitation and adsorption by Fe and Al oxides and CaCO3, easily immobilize phosphorus in soil. Herbivores and other animals obtain this element from plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.

OR

The accumulation of toxic component that increase in each successive trophic levels is called biomagnification. With each increasing trophic level biomagnification increases.
Example, in case of DDT accumulation, the primary consumers have the least concentration of DDT. With each successive trophic level DDT concentration increases. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations. Human beings consuming fishes with high levels of DDT can be hazardous for health.