How Does a Leaf Breath

Fill a large clear plastic bowl full of luke warm water and take it outside. Once outside you'll want to remove a leaf from a tree or plant and not just pick one up off the ground as we want an 'active' leaf for the project. Place the leaf in the bowl of water and put a small rock on top of it so it is FULLY submerged under the water. Then put the bowl in a sunny spot. If you have a place inside that's super sunny, you can also try keeping the bowl there. Oh yea, did I mention that now we need to wait a few hours ;) I know -- one of the hardest things for kids.  So go on with your day -- maybe set the experiment up before lunch or quiet time.   

What you should be seeing is small bubbles that form around the leaf and the edges of the bowl. Ask the kids what would happen if they held their breath, went underwater in the pool and then let their breath out -- they would see bubbles coming up in the water. That's what they are seeing here -- the leaf is still using the sunlight as part of the photosynthesis process (where leaves convert sunlight to energy).  As a leaf creates that energy, it needs to get rid of the items it no longer needs so it will expel both water and oxygen during a process called transpiration. This is why we see the bubbles -- as the leaf gives off oxygen when it is submerged and the oxygen can be seen as bubbles in the water. And since oxygen is lighter than water, the bubbles will eventually rise to the surface.
Now does a leaf breathe the same as we (humans) do?
Nope! Leaves don’t have any lungs or respiratory system.
But it is a living organism just like we are! So, there you have it -- you can tell the kid they are 'seeing the invisible' because when leaves are on the tree, you aren't able to really see them breathe.