Ça functions as a pronoun; ce is an adjective that must modify a noun (usually; some of the uses get a little complex).
This is something I would like to know also! How is it used to mean "take down"?????? Calling all French experts, please advise!
It's actually not as weird as you might think. The verb "pendre" means "to hang", such as a painting, etc., on the wall. So "dépendre" means "to take down" (painting, decoration, flag, etc).