(d) : Mesosomes are complex, intracellular, membranous structures within the cytoplasm, that are formed by the in foldings of the cytoplasmic membrane. Surface of mesosomes have many enzymes which take part in respiration e.g., oxidases and dehydrogenases. Mesosomes are also known to help in the separation of two daughter molecules of DNA during cell division. They are also called mitochondria of bacterial cell. Ribosomes are cytoplasmic organelles that occur in both prokaryotes and eukaryotes. When plasmids associate temporarily with nucleoid these are called as episomes.