Final answer:
Cellular division that supports clonal expansion is mitosis, and clonal selection and expansion are essential in the immune system to increase specific immune cells.
Step-by-step explanation:
The method of cellular division that provides clonal expansion of the population is mitosis. Unicellular organisms such as bacteria and yeast reproduce asexually through binary fission, which is a form of cellular cloning. In higher organisms, clonal selection and expansion are crucial processes in the immune system. For instance, stem cells differentiate into T cells with specific receptors, and those clones that have receptors specific for antigens on the pathogen are selected for and expanded.
This ensures that the numbers of specific cells equipped to fight the identified pathogen increase, which is a vital part of the body's adaptive immune response. Similarly, B cells undergo clonal selection and expansion, where only B cells with appropriate antigen specificity are selected for and expanded, leading to the production of plasma cells that secrete antibodies to fight the pathogens.