You can see this video clip from the BBC (TV series Botany: A Blooming History) which introduces the role of stomata.

The surface structure of a leaf is observed using increasingly larger magnifications. We can see the detail of stomata. The absorption of carbon dioxide through stomata is discussed and linked to the structural features of a tree.

The idea of stomata and their density on the leaf surface is often a difficult one to relay to students. Students can then do practical work making ‘prints’ of a leaf surface using nail varnish. They can investigate stomatal distribution in relation to adaptations of plants to their environment. This can be used as an introduction to leaf structure and then developed into a discussion of the other features of a leaf and how it is adapted for efficient photosynthesis. The mechanisms for the opening and closing of stomata can also be developed with older students, as well as plant strategies for dealing with water stress - also linked to stomatal action. The final section which links an exhaled breath to the bark of a tree can be used as stimulus for a synoptic mind mapping exercise to bring together all that a student may know about plant growth and photosynthesis.

See this on the BBC Four Botany: A Blooming History