Humans belong to the domain Eukaryota. This domain includes four of the six kingdoms of life: Protista, Fungi, Plantae and Animalia. The other two domains are Archaea and Bacteria.
The domain Eukaryota includes all organisms that have membrane-bound structures called organelles, which include the nucleus, mitochondria and chloroplasts. The most diverse group in Eukaryota is the protist kingdom. Some scientists do not think that the protists should be lumped together in one kingdom.
The other two domains contain organisms that do not have organelles. These organisms are called prokaryotes and consists of bacteria. While the domain Bacteria consists of the common bacteria with which humans often come into contact, the domain Archaea contains the bacteria not often encountered, such as the organisms living in extreme environments, including those thriving in the deep sea vents or salty lakes.