All living organisms are composed of small, tiny structures or compartments called cells. These cells are called the ‘building blocks’ of life.The cells in a true sense are considered as the basic unit of life because all the life processes, i.e., metabolism, responsiveness and reproduction are carried out by the cells. Cells are the seat of all metabolic processes. Respiration, nutrition and release of energy are carried out within the cells. Even the animals and plants reproduce because the cells reproduce individually. Growth occurs because cells grow and multiply.Let us take the example of amoeba, a unicellular organism. In amoeba, all the life processes are performed within the boundaries of the single cell. On the other hand, the body of a multi cellular organism is made up of many cells. In these organisms, the cells do not behave independently, but get organized into tissues. Each tissue is specialized to perform specific functions. Different tissues then get organized into organs, which perform certain specific functions. Different organs are finally organized to form organ systems. These tissues, organs and organ systems of the organisms work because the cells work.On account of the above discussion, it can be said that cells are the structural and functional unit of living beings. Hence it is the basic unit of life.