An atom, a cell, and a molecule are fundamental units that make up matter and living organisms, but they are distinctly different in structure and function.
Atom: An atom is the basic unit of matter. It consists of a nucleus, made up of protons and neutrons, surrounded by electrons that orbit the nucleus. Atoms are the building blocks of everything in the universe, from the air we breathe to the solid objects we touch. For example, a single helium atom is made up of two protons, two neutrons, and two electrons.
Molecule: A molecule is formed when two or more atoms bond together chemically. These relationships can be between the same type of atoms, such as in oxygen (O2), or different types, like in water (H2O). Molecules have distinct properties that differ from the atoms that make them up, and they form the basis of chemical compounds.
Cell: A cell is the smallest unit of life, containing various organelles and structures needed to perform vital functions. Cells are composed of multiple molecules, which in turn are made up of atoms. Cells can be simple, like bacteria, or complex, like human cells, and they are responsible for carrying out all the processes necessary for living organisms.
In summary, atoms are the smallest units of elements, molecules are combinations of atoms bonded together, and cells are the smallest units of life comprised of various molecules working together to sustain life.