The cell is the basic unit of life. Just like how snow makes up snowmen, and how  sand makes up sandcastles, cells make up living things.

Check out this cool video to see what cells look like:

Cells from animals look different from cells in plants. Cells in animals are usually round, and cells in plants are more rectangular.

Think of animal cells as squishy balls with lots of stuff inside.

Cells are very, very, very small. Some cells are smaller than other cells. A skin cell is 30 micrometers long.  That is almost 17 times smaller than this grain of salt in my hands. A red blood cell is 8 micrometers long.  That is almost 63 times smaller than this grain of salt.

Trust me, cells are very small. You can't see 1 animal cell by itself without a microscope. However, if you put billions and trillions of cells together, then you get an organism, like you. Bigger organisms have more cells. In fact, when you are all grown up, you will be made up of around 100 trillion cells! 

Here is 100 trillion written out:

100,000,000,000,000

Yep, that's a lot of cells. Why do we need so many? Let's find out by looking at the cell theory.