All living things are made up of cells. Some living things, like bacteria, are made of just one cell. Humans are quite complex living things – each one of us is made of roughly 40 trillion human cells!
Put an onion under the microscope and you’ll see how it’s cells fit together like bricks. Image by Kaibara87 for Wikimedia
When cells break the rules and start dividing too quickly, cancer can develop. Scientists are trying to understand what the rules are and why some cells break them, so we can invent new cancer treatments. Scientists are now growing cells outside of the human body, in the lab. By creating the right conditions they can grow whole organs from just a few cells. In the future these organs could help treat disease or be used in organ transplants.