We have been studying microorganisms as part of our Classification work in Science, and we conducted an experiment to see which food substance yeast (a microorganism) preferred to feed on. As the yeast ate our sample of sugar, it released a gas called carbon dioxide. The gas filled the bag and then carried on filling the bag as more gas was created - at one point, Horowitz and Morpurgo Classes were worried the bag would explode! We discovered that each bit of yeast makes tiny gas bubbles and that puts millions of bubbles (holes) in our bread before it gets baked. We were surprised to see more gas had formed with the sugar than with the flour sample - this is because sugar speeds up the fermentation process.