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That is a mystery all unto itself. It is a complex organism that is generally composed of then systems; integumentary, skeletal, muscular, nervous, endocrine, circulatory, digestive, respiratory, urinary, and reproductive. These systems are composed of organs, such as the heart, lungs, stomach, intestines, brain, etc. These in turn are made of specialized tissues that come in four categories; connective, nervous, muscular, and epithelial. Finally, these tissues are made of specialized cells, about 100 trillion of them, and science has yet to figure out what actually makes them alive.

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17y ago

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