Answer: The correct answer for the blank is - Nucleus.
Cytoplasm is the fluid filled compartment of the cell that is surrounded by plasma membrane and possesses all the contents of a biological cell excluding the nucleus (which contains the genetic material of eukaryotes).
It is the site for majority of the metabolic reactions that are essential for the cell.
Cytoplasm holds all the organelles (subcellular components such as ribosome, mitochondria, golgi complex, endoplasmic reticulum) except nucleus.
Thus, nucleus is the right answer for for the blank.
