So you've already learned that Lewinhuk was the first person to observe the world of the microbes, the world of tiny living things that we cannot see without a microscope. In the time that Lewinhuk investigated the world of the micro, some of the first ones that he saw were what we today we call protozoa. These are relatively large cells still need a microscope and these cells here are about the same size as the cells that make up your body. Another major group of living things that Lewinhuk saw were the fungal cells. These cells are just as large as protozoal cells but some of the fungal groups actually grow much larger and form structures that you and I call toad stoles and mushrooms but here on this course we're only concerned with the single cell fungi which are the microbes the so-called yeast cells. So Lewinhuk saw both of these groups. Another group that Lewinhuk saw were the bacterial cells. He was the first person to see these as well. In this image we have the bacteria known as E coli, that's his name and this is a famous bacteria often associated with diseases such as food poisoning. A group which Lewinhuk did not see were the viruses. The viruses were not seen until the 1960s with the invention of the electron microscope. In this image is a virus known as SAR, COV2. This is the virus that is the cause of the disease COVID-19. COVID-19 is the disease. This is the name of the bacteria, a big important. This is the name of the virus and this image here is one of the viruses that cause that disease. These are the four major groups of microbes, protuzoa, fungi, bacteria and viruses.