The pink balloon is Period 4's demonstration while the purple is Period 5's. The setups were the same. Each flask contains apple cider yet the the + labelled flasks also contain yeast. To each flask a deflated balloon was added to starve the flask of oxygen from the atmosphere, creating the conditions for fermentation. As can be seen, the + labelled flasks performed alcoholic fermentation by the yeast creating carbon dioxide as a waste product. Because of this, the balloon inflated. Without the yeast in the - labelled flasks, no fermentation occurred, creating no carbon dioxide which prevented the balloon from inflating.
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