Describe stem cells, stem cell division and differentiation, and the role of specialized cells in complex organisms, such as humans.

Stem cells are the primal cells which develop from adult body tissues and embryos. These are present in the adult body through out their life. These are also called tissue specific or somatic stem cells. These are more specialised than embryonic stem cells. These stem cells are found in bone marrow, brain, blood and blood vessels, skeletal muscles, skin and the liver. Differentiation is the process where an unspecialised cell acquire cellular character which allows it to perform specialised functions. During embryonic stage, the cells of embryo make a number of cell fate decision that result in the decreasing capability eventually producing the specialised cells. Stem cells can divide and produce new cells, Hence they have the potential to be transplanted to the patient to treat medical conditions and disease. They are removed form the embryo where they exist as unspecialised stem cells and they will differentiate into any cell type. Specialised cells include many cells like nerve cells, blood cells, ovum cells etc. These specialised cells help in reproduction, energy metabolism, regeneration, information transfer etc.

poor water quality affects most estuarine organisms, including commercially important fish and shellfish. the pollutants that have the greatest impact on the health of estuaries include toxic substances like chemicals and heavy metals, nutrient pollution (or eutrophication), and pathogens such as bacteria or viruses.