From bacteria to humans, cells give all living things their structure and functionality. They are regarded as the tiniest form of life by scientists. The biological machinery that creates the proteins, chemicals, and signals essential to every bodily function is housed within cells. Different cell forms include round, flat, long, starshaped, cubed, and even shapeless ones. Most cells are transparent and colorless. A cell's size varies as well. One-celled bacteria, which measure one millionth of a m (or µm) across and are too tiny to be seen with the human eye, are among the tiniest organisms. The biggest cells, measuring between 10 µm and 100 µm, are found in plants. The egg is the human cell with the largest diameter. It has a diameter similar to a hair strand (80 µm).
