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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Adolescents often feel clumsy during puberty because during this time of development, their hands and feet grow faster than their arms and legs do. The body is therefore out of proportion. One out of five adolescents actually experiences growing pains during this period.
There are more nerve cells in one human brain than there are stars in the Milky Way.
IgA antibodies protect body surfaces exposed to outside foreign substances. IgG antibodies are found in all body fluids. IgM antibodies are the first type of antibody made in response to an infection. IgE antibody levels are often high in people with allergies. IgD antibodies are found in tissues lining the abdomen and chest.