Yeast Lab

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Yeast fermentation

Hypothesis - Yeast cells perform fermentation when supplied with a source of energy.


Two 250 mL Erlenmeyer flask Water, Sugar solution Bromothymol blue solution plastic tubing Rubber tubing Two rubber stopper 50 mL graduated cylinder Medicine dropper Blank slide Cover slip Microscope Yeast, Tape

Procedure - Part one Pour 30 mL of water into a flask. Add a packet of yeast into the flask. Add 50 mL of bromothymol blue solution to an empty flask. Place a stopper apparatus into the blue flask. Add 50 mL of sugar solution into the yeast flask. Place the other end of the stopper apparatus into the flask containing yeast, tape the stopper in place. Swirl the flask gently for 30 seconds.

Part two The next day observe and record any changes in the two flasks. Remove the stopper from the yeast flask describe any odor you detect. Using the dropper take so yeast mixture from the bottom of the solution. Use a drop to make a slide. Observe the side under low, medium, and high power. Draw the yeast cells as accurate as possible. Comment on their size, shape, behavior, and number.


Day 1 yeast flask: small little spheres floating in the water looks a lot like oatmeal Day 1 blue flask: very dark blue liquid
Day 2 yeast flask: still looks like oatmeal very foamy
Day 2 blue flask: the liquid turn from blue to a light green


The substance that causes the Bromothymol blue to change color to green is the carbon dioxide. This carbon dioxide gas was produced by fermentation process...
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