Most living things that are visible to the naked eye in their adult form are eukaryotes , including humans . However, a large number of eukaryotes are also microorganisms. Unlike bacteria and archaea , eukaryotes contain organelles such as the cell nucleus , the Golgi apparatus and mitochondria in their cells . The nucleus is an organelle that houses the DNA that makes up a cell's genome. DNA (Deoxyribonuclaic acid) itself is arranged in complex chromosomes .  Mitochondria are organelles vital in metabolism as they are the site of the citric acid cycle and oxidative phosphorylation . They evolved from symbiotic bacteria and retain a remnant genome.  Like bacteria, plant cells have cell walls , and contain organelles such as chloroplasts in addition to the organelles in other eukaryotes. Chloroplasts produce energy from light by photosynthesis , and were also originally symbiotic bacteria .