Which of the following is considered the smallest unit of life?

The cell is considered the smallest unit of life because it is the fundamental structural and functional unit of all living organisms. Cells are capable of performing all life processes, including metabolism, growth, reproduction, and response to stimuli. They are the building blocks of more complex structures, such as tissues and organs, and can exist as individual organisms themselves, such as in the case of unicellular organisms like bacteria.

In contrast, while atoms and molecules are essential components of cells, they do not exhibit the characteristics of life on their own. An atom is the smallest unit of matter and a molecule is a group of atoms bonded together, but neither can independently carry out the life processes associated with living organisms. Tissues, on the other hand, are made up of groups of similar cells that work together to perform a specific function, but they depend on the function of cells. Thus, the cell is the correct answer because it embodies the properties of life in a way that atoms, molecules, and tissues do not.