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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.
The human body's pharmacokinetics are quite varied. Our hair holds onto drugs longer than our urine, blood, or saliva. For example, alcohol can be detected in the hair for up to 90 days after it was consumed. The same is true for marijuana, cocaine, ecstasy, heroin, methamphetamine, and nicotine.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.