Britannica Educational Publishing 
Closer Look at Bacteria, Algae, and Protozoa [PDF ebook] 

Bacteria, algae, and protozoa-microorganisms that are easily overlooked in our daily lives-can be found in a wide variety of locations and serve innumerable ecological purposes. While some such organisms have been associated with disease, they have also been invaluable in agriculture and in the production of certain foods, medicines, and other necessities. This informative volume examines the properties and uses of these powerful and essential life forms. Graphic organizers and detailed images bring the miniscule details of these entities to the forefront.