Is+Yeast+Alive?

Yeast will produce carbon dioxide when sugar is available. However, no gas will be produced when no sugar or other foods are present.
 * Hypothesis:**

Yeast, being living things will respire when given the necessary conditions. Food, in this case glucose, is necessary for respiration to occur in the yeast. Therefore, only when sugar is present will the yeast be able to respire and thus produce of carbon dioxide.
 * Reasoning:**

When the gas in the test tubes were bubbled into the limewater, a white precipitate is formed for the test tube with yeast added to warm glucose solutions, which shows that carbon dioxide was produced. However, yeast added to warm water did not produce any gas that caused a precipitate to form in the limewater, which means no carbon dioxide was produced. Also, when methylene blue was added to the test tubes A and B with warm yeast solution and boiled yeast solution respectively, the contents in test tube A turned back to the original colour while the other remained blue. When shaken, the solution in test tube A frothed, while no froth was observed for the solution in test tube B. Carbon dioxide was produced when the yeast was given glucose, which indicates that respiration had occured. This did not happen when the yeast was not given any glucose, which proved that the yeast was alive and had been able to respire, thus producing the carbon dioxide as observed. Also the contents of the test tube turned back to the original yellow,which shows that the yeast was able to reduce the methylene blue, and thus shows that it is alive. When yeast is added, it respires and produces carbon dioxide, which causes the dough to rise. Yes. The yeast will multiply rapidly.
 * Discussion:**
 * **Discuss the results you obtained with your partner. How do you interpret your results.**
 * **What are the evidences that prove that the yeast cells are alive?**
 * **When you make bread, if you just mix flour, sugar and water, the dough does not rise and the bread will be flat and hard. If you include yeast in the bread dough, then the dough rises and the bread is bigger and fluffier. Can you explain how the yeast helps the bread dough to rise?**
 * **If we were to place a few grains of yeast in a yeast culture, do you think you will be able to see any growth after a day or two?**