As part of my 4th grade science we learn about ecosystems. Our signature saguaro cactus is a great way to bring home some plant knowledge about survival in the surrounding desert. We read the book Mojave by Diane Siebert and do some art with the cactus as well as a found poem with the book. I'll try to dig up a sample of that for you soon.
One easy and quick thing I do to show the kids how the cactus survives in the desert with so little water is to demonstrate how the cactus actually stores water long term.
I just accordion fold and staple two pieces of construction paper long ways. Since I was at home for this post I just have one piece but you can get the idea.
Cue the lovely 5 year old model in my kitchen:
You can see here that the cactus is skinny and the spines are well pronounced. This is what the cactus looks like when it has very little water stored.
But when it rains and the cactus sucks up some water with its roots, it stores the water in the middle. This causes the "dips" in the folds to move outward and the cactus actually gets wider, the ribs less pronounced.
When the cactus goes for long periods without water, it uses up the water and the ribs slowly become more pronounced again.
Easy, quick visual for desert plant adaptations!