Leaves
Stomata
All leaves have tiny pores that are used for gas exchange. These pores are called stomata (singular: stoma), and are usually found on the underside of a leaf. To prevent dehydration through open pores, a pair of guard cells surrounds each stoma to regulate its opening and closing. At this exhibit, you can see clear pictures of stomata and guard cells underneath a microscope.
The guard cells are green since they contain chloroplasts.
Why use this plant? Although all plants have stomata, the purple background of this plant makes it easier to see the green gaurd cells and pores.