The two kingdom classification system was given by Linnaeus in 1758. Lesser number of organisms were known then in comparison to what the world knows today. He classified all the known living beings into two categories-Animalia and Plantae on the basis of the presence or absence of cell wall in their cells. As bacteria, blue-green algae, fungi, algae, mosses, ferns, gymnosperms and angiosperms have their cells surrounded by cell walls, unlike animals, therefore, they were placed together under kingdom-Plantae.