What is the primary function of the nucleus in a cell?

The primary function of the nucleus in a cell is to serve as the control center that houses the cell's genetic material, or DNA. This function is critical for regulating gene expression, which ultimately determines how a cell functions and responds to its environment. The nucleus plays a key role in processes such as cell growth, replication, and differentiation by controlling the synthesis of proteins through the transcription of DNA into messenger RNA (mRNA).

While the other options relate to important cellular functions, they do not describe the primary role of the nucleus. For instance, energy storage is typically handled by other organelles, such as mitochondria and chloroplasts. The protective wall aspect refers to the cell membrane or cell wall, which regulates the entry and exit of substances. Transporting materials is more closely associated with structures such as the endoplasmic reticulum and vesicles. Therefore, the correct answer reflects the essential role the nucleus plays in managing cellular activities through genetic control.