What defines non-membranous organelles?

Non-membranous organelles are defined by the fact that they are not enclosed by a membrane, allowing them to be directly immersed in the cytosol of the cell. This characteristic enables these organelles to readily interact with the cytoplasmic contents, facilitating various cellular functions. Examples of non-membranous organelles include ribosomes and cytoskeletal elements. Since they lack a membrane, they are distinct from membranous organelles, which are surrounded by lipid bilayers and have more compartmentalized functions within the cell.

The notion that non-membranous organelles are always in touch with the cytosol further clarifies their role—they directly participate in the cell's metabolic processes without any separation that a membrane would create. This is a critical factor in their functionality, as they can rapidly exchange materials and signals with the cytoplasm and engage in protein synthesis, structural support, and other essential activities.