What is the dense, active protoplasm located in the center of the cell called?

The dense, active protoplasm located in the center of the cell is referred to as the nucleus. The nucleus serves as the control center of the cell, containing the cell's genetic material (DNA) and coordinating activities such as growth, metabolism, protein synthesis, and cell division. It plays a crucial role in ensuring that the cell's functions are properly regulated and maintained.

In contrast to the nucleus, the cytoplasm refers to the fluid and structures within the cell membrane but outside of the nucleus, playing a role in cellular processes but not serving as the central command like the nucleus does. The term organelle describes specialized structures within the cytoplasm that perform various functions, such as mitochondria or the Golgi apparatus, but again, these are not located at the center of the cell nor are they the active protoplasm responsible for cell regulation. A cell membrane is the outer boundary of the cell that protects its contents and maintains its integrity but does not contain the active protoplasm itself.

Thus, the nucleus stands out as the key central feature of the cell that houses genetic information and directs cellular activities.