Bacteria are tiny organisms that can only be seen by a very high-powered microscope. Blue green algae from the Archaic Era 3.5 billion year ago was actually a bacteria. There are helpful and harmful bacteria in the world. Helpful bacteria makes yogurt. One type of harmful bacteria gives you strep throat.
Protists are one celled organisms.
Like the bacteria, protists are very tiny and still need a microscope to be seen. Protists evolved about 1.5 billion years ago. The diatom, amoeba and algae are protists. They need to find energy and chemicals by growing on a source of food. Then they release chemicals on the food they are eating.