The smallest structural and functional component of protoplasm that can exist freely is the cell (Suntharalingam et al, 2005, p. 485). It is just necessary to study the effects of radiation at the cellular level to truly understand the factors that affect biological tissues. Cells are of two types - somatic cells and germ cells. Of these somatic cells have three subtypes - stem cells (cells that generate other cells through differentiation), transit cells (cells that are in the state of being transformed from one type of cell to another) and mature cells (cells that are fully differentiated and are relatively stable in that state) (Suntharalingam et al, 2005, p. 487). Somatic cells proliferate through two well-defined time periods - mitosis (M), when cell division takes place while maintaining the species chromosome number; and the period of DNA synthesis (S). (Suntharalingam et al, 2005, p. 487). Before S, there is a gap (rest period) when DNA is not yet synthesized. After S there is another gap (when DNA is synthesized but other metabolic processes are taking place). After M takes place. Thus, the cell proliferation cycle is - S M. In time this whole process is - (1-8h) S (6-8h) (2-4h) M (>1h) (h = hours). Thus, the entire cell proliferation cycle can take between 10 to 20 hrs (Suntharalingam et al, 2005, p. 487).
When there is death among non-prol ...Show more