The cell is considered the basic unit of life in all living organisms. Every living organism, from the simplest bacteria to complex animals like humans, is made up of cells. Some organisms, like bacteria, are unicellular, meaning they consist of just one cell, while others, like humans, are multicellular, composed of trillions of cells. Cells carry out essential functions such as obtaining nutrients, converting energy, and reproducing, which are vital for the organism's survival.