Type |
Description |
Examples |
Some Disorders That Can Result |
Bacteria are microscopic, single-celled organisms without a nucleus. |
Streptococcus pyogenes |
Pharyngitis (strep throat) |
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Escherichia coli |
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Viruses are small infectious organisms—much smaller than a fungus or bacterium. They cannot reproduce on their own. They must invade a living cell and use that cell’s machinery to reproduce. |
Varicella zoster |
Chickenpox and shingles |
|
Rhinovirus |
The common cold |
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Fungi are neither plants nor animals. Their size ranges from microscopic to easily seen with the naked eye. They include yeasts, molds, and mushrooms. |
Candida albicans |
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Trichophyton |
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Parasites are organisms that survive by living inside another usually much larger organism (the host). They include worms and single-celled organisms called protozoa (which, unlike bacteria, have a nucleus). |
Enterobius vermicularis (a species of pinworm) |
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Plasmodium falciparum (a species of protozoa) |