Basic unit of life is cell.
In unicellular organism like amoeba all metabolism is done by single cell.
While in multicellular organism, number of cells form tissue, number of tissues from organ, number of organs form organ system and number of organ system form organism.
So basically every organ in body is made of number of cells which uses ATP as energy source .

Basic unit of life is cell since ot is structural and functional unit of life.

Hi Shibam, 

The Basic unit of life is cell.Cells as Building Blocks. A cell is the smallest unit of a living thing. A living thing, whether made of one cell (like bacteria) or many cells (like a human), is called an organism. Thus, cells are the basic building blocks of all organisms.

Cell is the basic structural and functional unit of Life.

Hi Shibam,

The cell is basic structural and functional unit of life. A cell is capable of independently carrying out all the necessary activities of life. That's why it is called as basic unit of life.

All the best!!

Cell is the basic unit of life.. follow ncert of biology of class xi for more details.
Good luck.