You can demonstrate cellular respiration by dissolving yeast in white grape juice.
Pour 150-200 mL of white grape juice in one boiling flask, and the same amount of water in another boiling flask. Dissolve a few grams of yeast in each flask. Place an uninflated balloon over the mouth of each flask, and place both flasks in a warm place out of direct sunlight. Within hours you should begin to see bubbles forming in the flask with grape juice, and within a day the balloon attached to that same flask should begin to fill with carbon dioxide. The flask with water and yeast should not show any activity.