What structure in a cell is responsible for controlling cell activities like growth and reproduction?

The nucleus is the structure in a cell that is primarily responsible for controlling cell activities such as growth, reproduction, and metabolism. It houses the cell's genetic material, DNA, which contains the instructions necessary for building proteins and regulating various cellular functions. The nucleus orchestrates the expression of genes that lead to the production of proteins, which are essential for all cellular processes.

This regulation of gene expression is crucial for growth, as cells must produce specific proteins to support their development and function. Additionally, during cell reproduction, the nucleus plays a vital role by ensuring that DNA is accurately replicated and distributed to daughter cells.

Other structures, while important for the overall function of the cell, do not have the same direct role in controlling these essential activities. For instance, the cytoplasm is where many cellular processes occur, but it does not regulate activity. The cell membrane controls the movement of substances in and out of the cell and provides protection but does not direct cellular functions. Mitochondria are known as the powerhouses of the cell, providing energy but are not involved in controlling growth and reproduction.