Here are the answers:
1. Sponge
2. Fire
3. The Heart


Here are 3 more, cause you bastards are too fast.


1. I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

2. When I am filled, I can point the way; When I am empty, Nothing moves me. I have two skins, One without and one within. What am I?

And this one you'll probably take a while to get..

3. I went into the woods and got it. I sat down to seek it. I brought it home with me because I couldn't find it. What is it?