Yeast Investigation

8th December 2017

Yesterday afternoon, we completed an investigation to understand what yeast needs to thrive. We set up two test tubes: one in a warm place and one in a cold place. In each of the test tubes, we placed in 1 teaspoon of yeast, 1 teaspoon of sugar and 15ml of warm water. We then placed a balloon over each test tube and observed them over a period of time.

Thomas W stated, “We need a control in the investigation also.” So in each area (warm and cold area), we also set up a control which included 1 teaspoon of talcum powder, 1 teaspoon of sugar and 15ml of warm water.

“The reason we needed a control was to show that it was the yeast that made the balloon inflate and not the sugar or the warm water; we needed something to compare against.” explained Daniel.

Over time, here are some observations we made:

TEST TUBE WITH YEAST The balloon inflated a lot. There was evidence of lots of effervescence (bubbling); these bubbles were filled with carbon dioxide. (Mikey) The balloon only inflated a little bit. Again, there was lots of bubbles which had risen the whole way up the test tube so there was some evidence of carbon dioxide being created. (Melody)
CONTROL TEST TUBE The balloon had not inflated. There were only a couple of bubbles on top of the liquid but this was due to us shaking the test tube. (Thomas O) This was just the same as the control in the warm area.

In the end, we understood that yeast is a mirco-organism. It is used to make bread rise and for brewing beer. In order for it to work, it needs warmth, sugar and then it produces a gas called carbon dioxide.

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