Define Unicellular Organisms and Multicellular Organisms

You may be aware that some organisms are made up of only one cell, while others have more than one cell. Well, the single-celled organisms are called as unicellular organisms, for example, bacteria and amoeba. These organisms are capable to breathe, divide and nourish. While, the organisms with more than one cell are termed as multicellular organisms, for example, humans, birds, reptiles and fish.