Which of the following is not a type of membrane-bound organelle in eukaryotic cells?

Ribosomes are not considered membrane-bound organelles in eukaryotic cells because they are not surrounded by a lipid bilayer membrane.

Ribosomes are essential cellular structures responsible for protein synthesis. They are composed of two subunits, a large and a small subunit, and are made up of ribosomal RNA (rRNA) and proteins. Ribosomes can be found in both prokaryotic and eukaryotic cells. Although ribosomes are not surrounded by a membrane, they can interact with other cellular structures such as the endoplasmic reticulum and the nuclear envelope during protein synthesis.