Cells with a well-defined nucleus are called______a_____and cells without a well-defined nucleus are called_____b_____.
a. eukaryote b. prokaryote
Cells are divided into two groups - prokaryotes and eukaryotes. Prokaryotes are cells without nucleus and eukaryotes are cells with nucleus. All the prokaryotes are unicellular organisms while eukaryotes can be unicellular or multicellular organisms.