What type of cells are known for being more complex and having membrane-bound organelles?

Eukaryotic cells are recognized for their complexity and the presence of membrane-bound organelles. These organelles, such as the nucleus, mitochondria, endoplasmic reticulum, and others, perform specialized functions within the cell, allowing for more intricate cellular processes and higher levels of organization. This compartmentalization enables eukaryotic cells to carry out complex metabolic activities efficiently and is a key characteristic distinguishing them from prokaryotic cells, which lack such organelles and are generally simpler in structure.

Prokaryotic cells, for instance, are typically smaller and do not have membrane-bound organelles, which limits their cellular complexity. Unicellular organisms can include both prokaryotic and eukaryotic cells, but this does not specifically highlight the complexity associated with membrane-bound organelles. The term "all cells" encompasses both types and does not specifically point to the complexity offered by eukaryotic cells. Therefore, eukaryotic cells are the clear answer, as they embody the more advanced cell structure due to the presence of these organelles.