What is the basic unit of life?

The basic unit of life is the cell. Cells are the smallest structural and functional units of living organisms, meaning they carry out all the essential processes necessary for life. Each cell can perform functions such as metabolism, growth, and reproduction, which are critical for maintaining the organism's overall health and behavior.

In multicellular organisms, cells can specialize to form various tissues and organs, but at their core, it is the cell that forms the basis of life. Every living thing, from simple unicellular organisms like bacteria to complex multicellular organisms like humans, is made up of cells.

An organism, while a living being, is composed of many cells working together. Tissue refers to a group of similar cells that perform a specific function, and an atom is the smallest unit of matter, which is not alive on its own. Thus, the correct answer highlights the fundamental role of the cell in the biological hierarchy.