Single-celled and multicellular both have structures that perform life processes. Cells are the building blocks of life in living organisms. They are crucial in the production of energy and the inherited traits and characteristics of particular organisms. Single-celled organisms are also referred to as Monads, which are composed of bacteria, archaea, and protozoa. Multicellular organisms are plants and animals that perform more complex processes than single-celled organisms. Cells in animals differ from cells in plants, in that plants have the capacity to produce their own food and nutrients for sustenance while animals can't do this.