- Archaea: Prokaryotes that do not have peptidoglycan cell walls.
- Eucarya: Organisms from the following kingdoms:
Kingdoms- Protista (Note: This is in the process of changing.)—algae, protozoa, slime
molds. - Fungi—one-celled yeasts, multicellular molds, and mushrooms.
- Plantae—moss, conifers, ferns, flowering plants, algae.
- Animalia—insects, worms, sponges, and vertebrates.
How Small Is a Microorganism?
Microorganisms are measured using the metric system, which is shown in Table
1.1 In order to give you some idea of the size of a microorganism, let’s compare
a microorganism to things that are familiar to you.
German shepherd 1 meter
Human gamete (egg) from a female ovary 1 millimeter
A human red blood cell 100 micrometers
A typical bacterium cell 10 micrometers
A virus 10 nanometers
An atom 0.1 nanometerYour Body Fights Back
Immunologyis the study of how an organism specifically defends itself against
infection by microorganisms. When a microorganism such as the bacterium
Streptococcus pyogenes, which can cause strep throat, invades your body, white
blood cells engulf the bacterial cells and digest it in an immune response called
phagocytosis. Phagocytosisis the ability of a cell to engulf and digest solid mate-
rials by the use of pseudopodsor “false feet.”
Phagocytosis was discovered in 1880 by Russian zoologist Elie Metchnikoff,
who was one of the first scientists to study immunology. Metchnikoff studied the
body’s defense against disease-causing agents and invading microorganisms. He
CHAPTER 1 The World of the Microorganism^7