The well known demonstration with a vacuum pump, sucking cigarette smoke through cotton wool or fibreglass, is impressive. Trap and condense the smoke to show the tar and find the pH of both with universal indicator. Use the apparatus to compare different cigarette brands, or make the demonstration quantitative rather than qualitative by weighing the fibreglass or the condensate.
Get a sheep's pluck and look at the gross appearance of the lungs and the trachea. It may also be possible to show the blood vessels connecting the heart and lungs. Demonstrate the sponginess and elasticity of lung tissue by inflating the lungs (use a foot pump and rubber tubing to do this!). Cut open a lung to show the internal structure and the branching tubes of the bronchial tree.
Nicotine - an alkaloid in tobacco - is what makes the cigarette addictive, and all standard texts deal with its effects on the body. Research other uses of nicotine - eg one is in insecticides; another is using an infusion of tobacco leaves to catch and kill immature eels in the Basque countrywww.buber.netBasqueFood Recently, tobacco plants have been genetically engineered to produce human proteins to combat the rabies virus www.newscientist.comarticle.ns?id=dn3790).