Answer:
Growth
Step-by-step explanation:
Growth is usually defined as the increasing amount of any substance or material in terms of its physical appearance, particularly in size.
In the given question, it can be referred to as the growth of cells. Cells are the fundamental unit of life, are all organisms are comprised of cells. Unicellular organisms are comprised of singular cells, whereas multi-cellular organisms are comprised of multiple cells.
In the case of a multi-cellular organism, the process in which the quantity of cells increases, in terms of size, number and volume, refers to the growth of cells.