Why is the cell called the structural and functional unit of life?

The cell is called the structural and functional unit of life because all living organisms are made up of cells, and it is within the cell that all life processes take place. Every organism, whether unicellular like bacteria or multicellular like humans, is made up of cells. 

Cells provide structure to the organism and carry out essential functions that sustain life. For example, cells perform processes like energy production, growth, reproduction, and waste removal.  Without cells, life as we know it would not exist. Hence, the cell is referred to as the basic building block or unit that makes up all life forms, carrying out all necessary functions of life.