What is DNA replication? When and why does it occur?

DNA replication is the biological process of producing two identical replicas of DNA from one orginal DNA molecule.

DNA replication occurs when the DNA strands unzip and the orginal strands of DNA serve as a template for new nucleotides to join and form a new strand. In needs to occur because existing cells divide to produce new cells.

answer; i believe the answer is hydraulic action;

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.