When I serialize a GameObject, what gets saved?

Hello. I am currently creating a game that will require a savegame feature. I have the basic outline done, and I know that I can serialize an int, string, bool, and a GameObject. I would like to know what exactly gets saved when I serialize a GameObject, named Player. Will It save things such as the object's location, rotation, and many of the variables that I have defined in script for things such as health, mana, and available weapons? Or will I have to write a function that gets all of this information and then serialize that instead of the GameObject?

Thank's for any help that you might be able to give me!