Which of the following is a principal part of the cell?

The principal part of the cell is the organelle, which refers to specialized structures within a cell that perform distinct processes necessary for the cell's life and functions. Organelles include the nucleus, mitochondria, endoplasmic reticulum, and others, each contributing to cellular operations such as energy production, protein synthesis, and waste management.

While the nucleus is a crucial organelle containing genetic material and directing cellular activities, it is just one component of the broader category of organelles. Chromosomes, found within the nucleus, carry genetic information, and vesicles play roles in transporting materials, but these are also specific functions or structures rather than encompassing the concept of a principal part of the cell in its entirety. Thus, the term organelle effectively conveys the essential and diverse structures that contribute to the overall functionality of a cell.