Which is the smallest structure of all living things?

• A. Cells
• B. Eyes
• C. Hair
• D. Feet

Answer: (A)

The fundamental unit that carries out the necessary life processes is the cell. Cells are the smallest units capable of metabolism, growth, and reproduction, and they form the building blocks of all living organisms. Some organisms consist of a single cell, while others are made up of many cells, but in all cases the cell is the smallest structure that can be alive and perform essential life functions.

The other options are larger, composite structures. An eye is an organ composed of multiple tissues and many cells working together; hair is a filament produced by hair follicles and not a standalone living unit; feet are limbs containing bones, muscles, nerves, and skin—again built from many cells.