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Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.
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.
The familiar sounds of your heart are made by the heart's valves as they open and close.
In the United States, an estimated 50 million unnecessary antibiotics are prescribed for viral respiratory infections.
In 1864, the first barbiturate (barbituric acid) was synthesized.