how long does a water molecule circulate in the water cycle?
answer
1.until it combines with a different type of molecule
2.usually about 10,000 years
3.until something drinks it
4.indefinitely; it is impossible to tell.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.