Cellular organisms are living entities made up of one or more cells, which are the basic units of life. These organisms can be classified into two main categories: unicellular organisms, consisting of a single cell, and multicellular organisms, which are composed of many cells working together. Examples of unicellular organisms include bacteria and amoebas, while plants, animals, and fungi are examples of multicellular organisms. Cells in cellular organisms perform essential functions such as metabolism, growth, and reproduction. They contain various structures called organelles, which carry out specific tasks. For instance, mitochondria produce energy, while ribosomes synthesize proteins. The organization and function of these cells are crucial for the survival and development of the organism.