What process is considered to be growth when it occurs in multicellular organism reproduction when it occurs in a unicellular organism ?

Cell division

Explanation:

Cell division can be define as the process by which the parent cell divides into daughter cells. It is the part of the cell cycle.

In multi-cellular organisms there is specialization of cells for performing different functions thus cell division is required for this purpose the cells divide and a mass of cell or tissue performs functions. These functions are necessary for the growth of the organisms.

In uni-cellular organisms the functions are few. Thus a single cell divides to produce multiple cells to produce the offspring. It is the mode of asexual reproduction.