What is the smallest unit of life?

The smallest unit of life is the cell. Cells are the fundamental building blocks of all living organisms. They can carry out all necessary life processes, including metabolism, growth, and reproduction. This capability distinguishes cells from atoms and molecules, which, while essential to the structural makeup of living organisms, do not exhibit the characteristics of life on their own.

An atom is the basic unit of matter, and while it constitutes the building blocks of molecules, it cannot perform biological functions independently. A molecule, which is made up of two or more atoms bonded together, serves as a foundational component of cellular structures and biological processes but is not considered a living unit itself.

Tissues are a collection of similar cells that work together to perform specific functions, but they are made up of cells, which are the actual smallest units of life. Thus, the cell stands out as the essential unit capable of sustaining life processes, making it the correct answer.