NUCLEUS
The organelle serves as the "brain" of the cell is option D. Nucleus.
The nucleus contains the cell's genetic material in the form of DNA, which holds the instructions for the cell's growth, development, and reproduction. It regulates gene expression by controlling which proteins the cell produces and when, thereby governing the cell's functions and activities.
The nucleus also oversees cellular processes by coordinating activities like cell division and metabolism. Without the nucleus, the cell would lack direction and the ability to properly function, much like how a brainlèss organism would be unable to coordinate its actions.
