The answer is the letter A.the cells ability to reproduce. As the cell increases in size, the relationship between the surface and the weight of the cell decreases. This change decreases the efficiency of the diffusion rate and the metabolism of the cells. Therefore, while the cell is larger it is less efficient. To maintain the effectiveness of the body, a large cell will be divided instead of continuing to grow. Multicellular organisms grow by increasing the number of cells instead of increasing the size of the cells.