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Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
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Side effects from substance abuse include nausea, dehydration, reduced productivitiy, and dependence. Though these effects usually worsen over time, the constant need for the substance often overcomes rational thinking.
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A cataract is a clouding of the eyes' natural lens. As we age, some clouding of the lens may occur. The first sign of a cataract is usually blurry vision. Although glasses and other visual aids may at first help a person with cataracts, surgery may become inevitable. Cataract surgery is very successful in restoring vision, and it is the most frequently performed surgery in the United States.
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Tobacco depletes the body of vitamins A, C, and E, which can result in any of the following: dry hair, dry skin, dry eyes, poor growth, night blindness, abscesses, insomnia, fatigue, reproductive system problems, sinusitis, pneumonia, frequent respiratory problems, skin disorders, weight loss, rickets, osteomalacia, nervousness, muscle spasms, leg cramps, extremity numbness, bone malformations, decayed teeth, difficulty in walking, irritability, restlessness, profuse sweating, increased uric acid (gout), joint damage, damaged red blood cells, destruction of nerves, infertility, miscarriage, and many types of cancer.
Species-rich floras of chalk grassland compared to species-poor floras of acid soils.
Changes in light quality with depth: (a) the rich colours on a shallow coral reef;
Reindeer standing on snow to avoid blood-sucking insects.
A dose-response curve describes the relationship between the quantity of the chemical entering the ...
Directional Terms
The air quality index