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The lipid bilayer is made of phospholipids. They are arranged in a double layer because one of their ends is attracted to water while the other is repelled by water.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
As the western states of America were settled, pioneers often had to drink rancid water from ponds and other sources. This often resulted in chronic diarrhea, causing many cases of dehydration and death that could have been avoided if clean water had been available.
The word drug comes from the Dutch word droog (meaning "dry"). For centuries, most drugs came from dried plants, hence the name.
According to the National Institute of Environmental Health Sciences, lung disease is the third leading killer in the United States, responsible for one in seven deaths. It is the leading cause of death among infants under the age of one year.