More questions from our first grade class:

Why do tree-frogs have sticky "hands?"  What makes them sticky?

Thanks, 
1C

Well, the easy answer to why tree-frogs have sticky hands is "to help them climb trees".

The frog's hands aren't sticky all over, they have special toepads that have a very complex structure that allows the frogs to stick. This structure is made up of lots of special cells that look like columns and will squeeze into even tiny cracks. The toepad also has lots of mucus glands, so when the frog is on a smooth surface (like a waxy leaf or glass) the surface tension makes it stick (like how a small drop of water can stick to a window).

I hope this explanation makes sense!