The smallest unit of our organization, our smallest part, is the cell. The cell is the building block of all living things, but you probably remembered that! Each human body is made up of over 100 trillion cells that have different structures and different functions. We have blood cells that carry oxygen to our muscles, and nerve cells that carry electrical impulses from our brains to the rest of our bodies. If the whole body is like a city, a cell is just one simple brick. WHAT IS THE MAIN IDEA