Which cell structure is primarily responsible for the control of cellular activities?

The nucleus is primarily responsible for controlling cellular activities because it serves as the command center of the cell. It contains the cell's genetic material, DNA, which contains the instructions for building proteins and regulating various functions necessary for life. The information in the DNA directs processes such as growth, metabolism, and reproduction by enabling the synthesis of specific proteins in response to the cell's needs.

The nucleus also participates in the regulation of gene expression, which allows cells to respond to environmental changes and maintain homeostasis. Therefore, when considering the central role of the nucleus in managing and directing the functions of the cell, it is clear why it is identified as the key structure in the control of cellular activities.