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, and they can independently carry out the essential processes of life. They are often referred to as the "building blocks" of life because all living organisms are composed of one or more cells.

In multicellular organisms, these cells specialize to perform various functions, contributing to the overall operation of the organism. Cells can reproduce, respond to environmental changes, grow, and carry out metabolism, thus meeting all criteria necessary to define life.

Tissues, organs, and organisms are all levels of organization built upon cells. Tissues are groups of similar cells working together for a specific function, organs are structures made up of different types of tissues working together, and organisms are entire living entities composed of various organ systems. Therefore, while they are crucial components of life, they are not the foundational unit of life itself.