Organelles are distinct structures within cells that carry out specific functions. In prokaryotes, organelles are not surrounded by membranes, while in eukaryotes they are. Prokaryotic cells have a cell membrane, cell wall, cytoplasm, and genetic material stored in a nucleoid. They may also contain features like pili, flagella, and a mesosome for cellular respiration. Ribosomes in prokaryotic cells are found freely in the cytoplasm.