Demonstrate how to use a ruler to measure centimeters or inches. Doing the Activity Ask children if they know the difference between living and nonliving things. Explain that every living thing is either a cell or made of cells. Cells are teeny tiny things that use fuel, grow, and reproduce. There are millions of cells on one tiny fir needle or on the tip of a child's nose.
Cells are usually visible only through a microscope.
Most children will volunteer that a living thing moves. Yet a car or bicycle move, and they are nonliving. Or they may insist a living thing can make noise or talk. Explain that the presence of growing and replicating cells clues us that an item is alive or, as in the examples of blood and mud, at least contain things that are alive. After you have discussed living and nonliving with children, explain that they will be comparing nonliving and living things.