All living organisms consist of one or more cells. Cells are the smallest units of life that can perform all the functions necessary for life, such as growth, reproduction, and response to stimuli.

Cells come in a variety of shapes and sizes. But they all share certain basic features, such as a cell membrane that separates the cell from its environment, genetic material in the form of DNA, and organelles that perform specific functions within the cell.

Cells can exist independently as single-celled organisms, such as bacteria, or they can work together to form multicellular organisms, such as animals, plants, and fungi.

The study of cells is called cell biology, and it's a key area of research in fields such as genetics, biochemistry, and medicine.