Plaque forming units

Plaque forming units are a way to count the number of viruses that can cause infections. Imagine there are some mean viruses in a bowl of soup. Scientists want to figure out how many of the viruses are in the soup. But they can't just look at the soup and count them like you count toys. That's because the viruses are too small to see with our eyes.

So instead, scientists will use a special method to count these viruses called plaque forming units. They use a little bit of the soup to grow more viruses in a dish. They put a tiny amount of the soup on the dish and let the virus grow for a few days. When the viruses have had enough time to grow, they cover the dish with a layer of bacteria that the viruses like to attack.

The virus starts infecting these bacteria, and the bacteria eventually die. This leaves behind a clear circle on the dish where the bacteria were killed by the virus. That clear circle on the dish is called a "plaque." Scientists then count the number of plaques on the dish and use that number to estimate how many viruses were in the original soup.

So, plaque forming units are just a way for scientists to count the tiny viruses that are too small to see with our eyes. They use a special method involving growing more viruses and then counting the number of clear circles made by the virus on a dish.