What is the simplest unit of life?

The simplest unit of life is the cell. Cells are the basic structural and functional units of all living organisms. They are capable of carrying out all the processes necessary for life, such as metabolism, growth, and reproduction. Each cell can maintain homeostasis, respond to stimuli, and perform vital functions that contribute to the organism's overall health and survival.

In contrast, while atoms and molecules are essential components of cells—serving as the building blocks of matter and forming the substances within cells—they do not possess the characteristics that define life. Tissues, on the other hand, are groups of similar cells that work together to perform a specific function, but they are a higher level of organization that relies on cells to exist. Therefore, among the provided options, the cell stands out as the fundamental unit that embodies the properties of life.