All living things are prokaryotes or eukaryotes and the difference is determined by the function and structure of their cells. Prokaryotes known as the first living organism on earth only process a membrane called the plasma membrane. They contain ribosomes and a nucleoid which also lack membranes. The eukaryotic cell is a complex structure that contains membrane-bound organelles, such as a nucleus in which genetic material is stored and organized. Prokaryotes are smaller in size than eukaryotic cells, they differ in the number of chromosomes, eukaryotes have more than one, and prokaryotic cells have only plasmids. They differ in cell type: eukaryotes are generally multicellular, and prokaryotes are in most cases unicellular. Eukaryotic organisms are animals and plants while prokaryotes are bacteria and archaea. Lysosomes and peroxisomes are present in eukaryotes and absent in prokaryotes. Cell walls are nonexistent in eukaryotic organisms except for some plants, and the cell walls of prokaryotes are generally made of peptidoglycan. Prokaryotes also differ in the density and arrangement of their genes. Prokaryotes are efficient and compact, containing little repetitive DNA while eukaryotes contain large quantities of non-coding DNA. Prokaryote genes are also found in groups known as operons, rather than individually, as in