What organelle does not have a membrane?
Well, technically all organelles have a membrane, so in the strict sense the answer to your question is: none. However, people often class ribosomes as organelles as they are ubiquitous and prominent components of cells. This is in spite of the fact that they have no membrane and so, by definition, are not organelles. To summarise: the strict answer to your question is all organelles are membrane-bound. Ribosomes, which are non-membrane-bound, are not organelles although they are frequently lumped in with them.
