GMAS 5th Grade Science Practice Test

Matter is made of tiny building blocks. The smallest unit that still has the properties of a substance is the atom. Atoms are the basic units of elements, meaning each element is made of one kind of atom. They can join with other atoms to form molecules, which are larger structures. A cell is a basic unit of life, not of all matter. An element describes what the substance is, not the smallest piece itself. So the atom is the correct choice because it’s the smallest unit that retains the properties of an element.