Get a plant that has been under-watered and is looking sad. Water it. Take a photo every 30 minutes after you’ve watered it, for a few hours, and see how they compare. Better yet, video it!
Make a bottle garden by putting a plant into a bottle that is half-filled with water (after stripping back the bottom leaves to allow it as much chance to root as possible – make sure none of the leaves are underwater or they may rot.). Let the plant grow in its own mini-greenhouse (a chance to learn about condensation) and watch the way the roots develop. Daily photographs will help you keep a visual diary of its growth – you may be surprised by the difference a sunny day can make.
Can you locate the places on the map using co-ordinates?