Which component is primarily involved in the regulation of cell activities?

The nucleus is primarily responsible for regulating cell activities because it contains the cell's genetic material, specifically DNA. This genetic material holds the instructions that guide the development, function, and reproduction of the cell. The nucleus acts like a control center, coordinating various cellular processes by controlling gene expression; it dictates when and how proteins are made, which in turn influences numerous cell functions such as metabolism, growth, and response to external signals.

The other components, while important for overall cell function, do not regulate activities in the same comprehensive way. The cytoplasm is primarily the site of metabolic processes and chemical reactions but does not control cell activities directly. The cell membrane plays a key role in controlling the entry and exit of substances, thereby influencing the cell's interactions with its environment but lacking the regulatory role of the nucleus. Mitochondria are essential for energy production, providing ATP through cellular respiration, but they do not manage or regulate overall cell activities.