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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.
Approximately 500,000 babies are born each year in the United States to teenage mothers.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
It is difficult to obtain enough calcium without consuming milk or other dairy foods.
Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.